How to check the cap of the expansion tank of the engine cooling system? Expansion tank: simple design and difficult problems.

Lid expansion tank car engine cooling system, as a rule, does not raise suspicions about serviceability. This, as many people think, a very “modest” detail in its significance, is entrusted with a very responsible task - to regulate the pressure in the cooling system. When the lid stops coping with it, in best case the liquid will boil or flow out, and in the worst case, this will lead to the breakdown of some nodes.

What is the main role of the tank cap?

A running engine, as you know, creates a pressure in the cooling system that is different from normal atmospheric pressure. This is due to the fact that (coolant) heats up along with the motor, as a result of which it expands - increases in volume. As a result, the pressure inside (SOD) increases, and it does not come into contact with the external environment, and there is nowhere for it to relieve excess pressure.

With increased pressure in the SOD developers modern cars do not fight "radically" - do not try to get rid of it completely. It is adjusted using the tank cap. The increased pressure in the SOD is used to shift the moment of boiling of the coolant. After all, it is no secret to anyone that at normal atmospheric pressure for water it occurs at a temperature of 100 ° C, for antifreeze - 105-110 ° C, and for antifreeze - 120 ° C. The operating temperature of modern car engines is very close to these critical values.

So, for example, for carburettor VAZ it should be in the range of 90-95 ° C, and for injection - 97-105 ° C.

However, under certain operating conditions of the engine, there is a short-term increase in its temperature to more high values, which, however, does not lead to the failure of a serviceable motor, but causes the same heating of the coolant. For example, on injection VAZ 2109 the liquid at such times can be 120–125 °C. Obviously, even antifreeze will not tolerate such heating. At the same time, an increase in the pressure of any liquid leads to an increase in its boiling point.

Engineers designing engines have long found out that so that the coolant does not boil even with a short-term critical heating of the motor, it is enough to maintain the pressure in the SOD at a level of 1.1–1.5 kgf / cm 2 (1.1–1.5 bar). More heat is not needed, because the engine is not designed for it, and it will lead to its failure. And it makes no sense to allow a greater spontaneous increase in pressure, which, nevertheless, can occur, because it will complicate the manufacturing and maintenance of the motor, as well as increase its cost, since it will require a stronger and tighter SOD (more durable nozzles and expansion tank, strong clamps).

Therefore, the tank lid must be airtight, but only up to the above required pressure limits, after reaching which it maintains them, connecting the system with the external environment as necessary to release the air compressed inside the expansion tank.

The device and principle of operation of the expansion tank cap

So that when the engine is running in the SOD, required pressure, the device of a cover provides dense tight closing of a tank. Provided to relieve excess pressure safety valve. It works (opens) only when the pressure inside the SOD becomes 1.1–1.5 kgf / cm 2 (depending on the design of the cover and its manufacturer).

While it is lower, the valve is closed, and immediately after the excess pressure has been released to a value that is less than the value indicated above - the partial release of air compressed in the tank - it closes. There is 1 more valve in the cover - inlet, it is also called vacuum. Its purpose is just the opposite of safety. Inlet valve serves for the intake (suction) of air in the SOD. The fact is that after stopping the engine, as you know, it begins to cool down. The coolant temperature drops as well.

At the same time, it decreases in volume, which is accompanied by a decrease in pressure inside the SOD. The coolant that has entered the tank, when it is heated, begins to go back into the system, making room for the air remaining in the expansion tank and ceasing to put pressure on it. Then there comes a moment when the pressure in the SOD is compared with the external atmospheric pressure. If at the same time the temperature of the coolant is higher than in external environment, then it, continuing to cool, will further decrease in volume.

This will lead to the fact that the pressure in the SOD will become lower than atmospheric, that is, to rarefaction, the vacuum effect. outside air will put pressure on the elements of the system and at the same time will seek to occupy its internal volume. If there is a “weak” place in any part of the SOD, where, when it cools and pressure is exerted from the outside, the tightness is broken, then air will enter the system, and a so-called air lock may form in it. When the engine is started again, it can, of course, be pushed out by the coolant into the expansion tank.

But if this does not happen, the air lock will disrupt the circulation of fluid in the SOD, prevent the motor from cooling, and may even cause it to fail. Usually air enters the system due to suction between the nozzles and fittings on which they are put on. To prevent this from happening, the pressure in the SOD equalizes with the external atmospheric inlet valve. It is triggered by a discharge in the system of 0.03–0.1 kgf / cm 2 and lets air into the expansion tank, which actually replaces the coolant pushed through the safety valve when heated. There is an alignment of the internal pressure in the SOD with the external one.

Signs and possible consequences of a defective part

Most often, the consequence of a malfunction of the cover is the boiling of the coolant, sometimes accompanied by the ejection of the latter from the expansion tank - a common occurrence for VAZ cars. If this happens at engine operating temperatures, then most likely the plug does not hold the necessary pressure.

Another reason for the same phenomenon is that due to a malfunction of the vacuum valve, air got into the SOD and formed a plug that disrupts normal circulation, and hence coolant cooling. In winter, due to the air lock, the stove may not work well. Unpleasant consequences: loss of coolant, which has to be regularly added. This happens when due to high blood pressure in the SOD, the liquid is “expelled” through the joints between the fittings and the nozzles put on them, through the clamps.

Disastrous consequences:

• rupture of low-quality pipes or those that have not changed for a long time (a picture familiar not only to VAZ owners);
• the appearance of a leak in the main or heating radiator;
• breaks the thermostat housing (for Nexia it is a common thing - into 2 parts);
• cracked expansion tank.

All these signs, the consequences of a malfunction of the cover, are the result of increased pressure in the SOD. The latter is not uncommon for VAZ 2108, 2109 and especially 2110 cars with new tanks. Of course, it is obvious that the plastic of these expansion tanks leaves much to be desired, but, nevertheless, it is also a matter of a malfunction of the plug. So the cover, regulating the pressure in the SOD, also protects its elements from mechanical damage.

How to check the cover and identify problems?

Before checking the expansion tank cap, it must first be inspected to make sure that it is intact and that it does not have mechanical damage in the form of scratches, cracks and heavy wear, and that there is no rust, dirt, scale and other flaws. Then you should check the performance of its valves. Some simple ways diagnostics, which allow only approximately determining their serviceability, is given below.

For safety valve. With the engine running, warmed up, twist the cover. There should be a hissing sound coming out of the tank compressed air. So the valve is holding pressure. But which one - not every professional will determine.

For vacuum:

• If the SOD pipes look deformed (compressed, flat) before the first start of the engine in the morning, the valve is definitely faulty.
• Unscrew and remove the cover. Then we strongly squeeze one of the SOD pipes and, holding it like that, put and twist the plug back. We let go of the tube. If he began to take his original shape - most likely, the valve is working.

More reliable way check the operation of the valves - use a pump with a pressure gauge for this. You will also need any empty expansion tank. We connect to one of its fittings, and then fix the pump hose with a clamp, from which the tip under the nipple was previously removed. The remaining conclusions from the tank are jammed with some kind of plugs. Then close the tank with a checked lid.

You can also check on the tank installed on your car without draining the coolant. To do this, for example, on the VAZ 2109, we disconnect the branch pipe from the expansion tank, which is suitable from above and removes steam from the SOD. Instead, install a pump hose. In order to muffle it, we insert something of a round section and a suitable diameter into the disconnected pipe, for example, a drill. Then we put a clamp on this hose and tighten it.

We turn on the pump and, observing the arrow of its pressure gauge, we fix the moment of a click, and then a hissing sound coming out of the tank through the air plug. If this happened at around 1.1–1.5 kgf / cm 2, and further pumping only leads to increased hissing, but the pressure does not increase, then the vacuum valve does not poison, and the safety valve works as expected.

Refinement of a new part - what to do if it does not function?

When it turns out that the cover is stubbornly unwilling to relieve excess pressure and/or is unable to restore air losses in the POD, it can be modified. Most of all, for some reason, complaints from the owners of the VAZ, model 2109, including those who buy new plugs. It is clear that the reason for the incorrect operation of the cover valves lies in the too high rigidity of their springs.

To finalize the cover, for example, for the VAZ 2109, it must first be disassembled. This must be done carefully, using pliers and a thin screwdriver with a flat sting. We must try to remember where everything was, so that the springs do not fly away God knows where. After the lid for the VAZ 2109 tank was disassembled, it's time for wire cutters. They need to shorten the springs: a large one, for a safety valve, as a rule, by 1 turn, and a small one by 2.

For the second, the length of the segment to be removed is not critical - as long as it supports the vacuum valve at all when it is closed and does not resist an outside air pressure of 0.03–0.1 kgf / cm 2. With a large spring it is more difficult - how not to overdo it. It is necessary to look at its rigidity and the pressure at which the safety valve opened when checking the cover of the VAZ 2109 tank. After shortening the springs, we assemble the cover in the reverse order. Before use, it is advisable to check once again how it works.

The attention of drivers who are accustomed to servicing their car on their own is usually riveted to the engine and chassis. Of course, these nodes are considered the main ones in the operation of the entire car. However, equal attention should be paid even to such seemingly insignificant details as the cap on the expansion tank. What role does this element play in the cooling system? Most drivers do not even realize that the quality of engine cooling depends entirely on this cover!

What is an expansion tank cap

Any driver, even the most inexperienced one, knows well what an expansion tank is for in a car. Coolant is poured into it, and the remaining free volume is designed to compensate for an increase or decrease in the amount of expanded liquid.

Accordingly, the tank is closed with a lid. The cover is installed on the neck of the tank in its upper part. Many drivers do not attach much importance to the lid - after all, it is important to simply maintain the tightness of the reservoir, and it does not matter what exactly to close it with.

Yes, the expansion tank cap is a locking element. However, contrary to popular belief, the lid has a complex structure and performs special functions.

Cover cavity includes rubber compressor and double valve train

What is an element made of?

The lid contains two valves. They are designed to protect the cooling system from possible damage due to overheating, in addition, these valves stabilize the operation of the entire system.

If you unscrew the cap from the tank and look at it internal structure, then you can see a kind of pressure control sensor.

Two valves are plugs of two closing springs

The lid must be tightly (without gaps) adjacent to the edges of the tank. For reliable connection, the sealing gum is included in the composition of the cover. Inside there are two valves:

• the first bleeds excess pressure in the tank;
• the second pumps the necessary pressure into the tank if the pump for some reason does not cope with its work.

These valves get their names from the use of high or low pressure: on VAZs, the first valve is called a safety valve, and the second is called a vacuum valve. However, both are at rest as long as the pressure in the tank is within the specified reading range.

Valve cover mechanisms on VAZs are springs

The driver cannot always notice malfunctions in the operation of the cover valves in time. It is simply impossible to make a visual diagnosis. But breakage of parts of the expansion tank cap can lead to serious problems with a motor unit.

Symptoms of a malfunctioning expansion tank cap

Car owners Russian production know how important it is to monitor the condition of all systems in the design of the machine. Even such a small element as the expansion tank cap can cause a lot of trouble - for example, if the valve mechanisms fail, the operation of the entire cooling system may be disrupted. As a result - overheating of the motor and jamming of the cylinders. The driver in this case is waiting for an expensive repair.

Therefore, to warn backfire, you need to carefully monitor while driving for some features in the behavior of the car:

• puffs of smoke appear from under the hood - therefore, the coolant has hit the hot surface of the intake manifold. Antifreeze could get on the collector for only one reason - the safety valve on the cover failed;
• cool air comes out of the stove, and the engine gets very hot: this is a sign of failure of the cover vacuum valve. Due to malfunctions in its operation, air jams occur in the cooling system, which leads to overheating of the motor;
• breaks in clamps, ruptures in hoses also indicate that the pressure in the system is unstable. And since it is the cap of the expansion tank that is responsible for the pressure, these symptoms indicate that it is time to replace or repair it.

If puffs of smoke come out from under the hood, this may indicate a malfunction of the expansion tank cap.

How to check the cover yourself on Prior, Grant, Kalina

It seems that it is enough to unscrew the cap from the expansion tank and inspect its insides in order to understand the specifics of the problem. However, it is not. For example, in service centers use special pressure pumps that can pump the right amount of atmosphere. By creating artificial pressure in the cooling system, the device allows you to calculate the correct operation of the valves.

The device for diagnosing the covers of the VAZ tank has a pressure gauge and a pump

But drivers don't have this expensive equipment, so they have to deal with what's in a standard garage. Diagnostics of the quality of the reservoir cap will be less accurate, but it will be possible to identify the main malfunctions of the valves:

1. Stop the engine.
2. Unscrew the cap from the neck of the tank.
3. Inspect the product for cracks, dents, chips. It could be that the sealing gasket is torn or badly worn.
4. In the event that there is no visible damage, the cover should be screwed back and the engine started.
5. Wait for the engine to warm up to its normal temperature.
6. Start slowly unscrewing the cap from the tank.
7. If a whistle of escaping air is heard during the unscrewing process (this sound can be compared with the release of gases when opening lemonade), then the lid is in working order, as it holds back pressure in the tank and hoses.
8. After that, turn off the engine again.
9. Check the pipes of the cooling system. If they are drawn inward, then the vacuum valve of the cover does not work well, since the pressure in the system is extremely low.

Photo gallery: algorithm for checking the operation of the lid

This typical scheme checking the expansion tank cap valves on all models of AvtoVAZ vehicles.

Checking the cover on the main VAZ models

Experienced Owners domestic cars made it a rule to change the cap from the expansion tank every two to three years. On the one hand, such attention to detail greatly simplifies the operation of the system. internal combustion engine cooling, and on the other hand, the cover costs less than 100 rubles, so absolutely every driver can afford to buy it.

Yes, and replacing the cover does not cause any difficulties. First you need to unscrew the cap from the tank on a cooled car. Then screw in the new one until it stops.

Video: lid health diagnostics

We check the cover on the VAZ 2108/2109

The design of the "eights" and "nines" produced by AvtoVAZ allows you to check the performance of the tank cover in one minute. The operation looks like this:

1. Open the hood of a car that has cooled down after driving.
2. Unscrew the cover of the expansion tank.
3. Squeeze the inlet hose as tightly as possible by hand.
4. At the same time screw the cap back on.
5. Then lower the hose.

If the compression site immediately acquires its original elasticity, then the valves on the cover are working properly. In the event that it cannot recover for a long time, it is recommended to replace the tank cap with a new one.

You can check the operation of the coolant reservoir cap on the VAZ 2109 with your own hands by simply squeezing the pipe with antifreeze

How to check the performance of the cover on the VAZ 2110/2111/2112

The procedure for checking the valves on the cap is the same as for previous models VAZ. The only caveat on the VAZ of the tenth family is that when the lid is unscrewed from the tank, the valve mechanism itself may fall out of the lid cavity. This is not a breakdown indicator, but, most likely, an unreliably fixed element will not work for a long time.

On the VAZ of the tenth family, the expansion tank cap tends to get out of the neck without valves

Checking the expansion tank cap on the VAZ 2113-2116

Diagnosis of the coolant reservoir cap on latest models WHA is as follows:

For a more accurate diagnosis of the tank cap, it is best to contact a specialized service center

However, on modern models VAZs are installing more complex valve mechanisms, which is why a check in the garage may not show breakdowns and malfunctions. It is recommended to contact the service center to check the cover on special pumping equipment.

The expansion tank cap on VAZ cars only looks like the simplest element. Inside the cover there are valves important for the entire cooling system that regulate the antifreeze pressure. It is recommended to replace the cover every two or three years - in this case, more than expensive repairs other elements of the cooling system.

How well do vehicle owners know their vehicle? After all, he is also prone to various diseases that need to be eliminated in a timely manner. The cooling system of any car (domestic or foreign production) deserves attention. It includes a special container, without which it is simply impossible to do, since it has the main role. However, any element of the system performs its task without them. efficient cooling engine is not possible. And if experienced drivers know how to check the expansion tank cap, then beginners may have difficulty.

The container is arranged simply, but this does not negate its importance. Many motorists consider the pump and radiator to be the most important components of the cooling system. Are they right? And what secrets can lie around such an inconspicuous and small detail as the expansion tank cap?

A small introduction

The expansion tank (RB) looks pretty simple: cheap and cheerful. But, despite this, it is impossible to simply take it and throw it out of the car. Such an insignificant, at first glance, detail can have its own problems, and there are many of them. Often they just explode high pressure, and the coolant (coolant) begins to fill the entire engine compartment.

For this reason, you should not wait until the tank can show itself at the most inopportune time. If a problem is found, do not postpone its solution indefinitely.

But before we figure out how to check the cover (or any other model), let's figure out what it is for and what important role performs. Maybe it would still be better without him?

An important element of the system

No one will argue that the engine cannot be without cooling, since it is necessary to maintain a certain temperature. Dealing with this successfully special liquid. A few decades ago, ordinary water was used for these purposes, and the upper tank of the radiator was used as a compensator, which was not completely filled. Now, drivers prefer antifreeze or antifreeze.

And here it is worth clarifying something. According to the laws of physics, a liquid expands when heated, and when boiled, it completely turns into steam. If water is heated to 100°C, its volume increases by 4.5%. The same thing happens with the liquids used, only a little more - 6%.

This leads to an increase in pressure in the cooling system. Because of this, there is a need for extra space in case of an increase in liquid volume. That's what the expansion tank is for. It compensates for the increase in the volume of antifreeze or antifreeze.

Tank device

To check the expansion tank cap of an Audi or any other car, you need to know how it works. For almost all models, this is a polypropylene case, which has a filler neck with lid and two nozzles, top and bottom. The lower outlets are connected to the main line of the cooling system, and excess vapors and air bubbles are discharged along the upper ones.

In modern cars, the design of the expansion tank is supplemented by float sensors that monitor the coolant level. To do this, the housing has another neck where the sensors are installed.

There are several control marks on the side of the container:

• lower risk - min;
• upper line - max.

The fluid level should be somewhere in between.

How an expansion tank works

Now it is worth touching the work of the tank. To begin with, it is worth giving the values ​​​​of the boiling point different liquids(at atmospheric pressure):

• water - 100 °C;
• antifreeze - 105-110 ° C;
• antifreeze - 120 °C.

Now you can understand why most drivers prefer to buy antifreeze. Considering the question of how to check the expansion tank cap of the VAZ 2114 (for example), it is worth delving a little into the theory. The boiling point of the coolant can be further raised by increasing the pressure above atmospheric pressure. For this reason, the entire system is securely sealed to maintain desired level pressure. The optimal value is 1.1-1.5 atmospheres.

However, high level rarefaction (0.03-0.1 kg / cm²) also does not benefit the engine. This can lead to air leakage into the cooling system, which will cause air locks. As a result, fluid circulation will be difficult, which ultimately leads to overheating of the motor.

The role of the tank cap

Now we know what the expansion tank is for. But here there may be one very interest Ask, what role is assigned to its cover? Just described above dangerous situation, which can occur with a strong rarefaction.

Many drivers, especially beginners, are not aware of how to check the expansion tank cap on a VAZ. Needless to say, they believe that it only acts as a locking device and does not allow the coolant to splash while the car is moving. This is partly true, and this element really works as a locking device. However, he has a much more important task.

As you know, the pressure in the cooling system must be maintained at the level of 1.1-1.5 atmospheres. The cover just copes with this task with a bang. How does she do it? The thing is that her device has two valves:

• safety;
• vacuum.

The first one looks like a spring-loaded rubber diaphragm that is pressed in from the outside. The second is a rubber washer with a small spring hidden inside a large one.

At normal system pressure, both valves are closed. The tank is sealed, so as the coolant temperature rises, so does the pressure. He just needs to get over permissible value as the safety valve opens and part of the air vapor is vented out.

When the car cools down, the volume of fluid in the system decreases, and due to the same tightness, a rarefaction occurs. This is where another valve comes into play - the vacuum valve. When it is opened, the system pressure is compared with the atmospheric value.

Location of the Republic of Belarus

To check the expansion tank, you need to know where it is located, which causes difficulties for some beginners. If we take into consideration domestic transport from the largest manufacturer AvtoVAZ, then, depending on specific model, it can be in different places.

For example, in the VAZ-2110-12 line, the tank is located with driver's side(in relation to the movement of the vehicle) between the shock absorber strut and the bulkhead of the passenger compartment. For VAZ-2114-15 models, the container is also on the left side, but placed behind the glass of the rack. Around the same place is the reservoir of the Audi 80.

Symptoms of a failed tank cap

All devices fail sooner or later, no matter how simple or complex they are. The expansion tank cap is no exception. Only the whole difficulty lies in the problematic diagnosis of her condition. And the consequences of its failure can be very serious.

How to check the operation of the expansion tank cap? But what is much more important - what can lead to the diagnosis of this part? In fact, the presence of the following signs:

• Smoke can be seen from under the hood.
• Engine overheating.

Smoke may come out due to the fact that the liquid has got on a hot intake manifold. At the same time, the engine temperature is within normal limits. This problem relevant in case of a faulty valve that opens earlier than necessary. For this reason, a splash of coolant occurs.

Overheating is often caused by a broken low pressure valve. As a result of his bad work plugs form in the cooling system, which leads to such a sad result.

In addition, the tearing of the clamps, as well as the rupture of the radiator, pipes or other elements of the system, including the tank itself, can be considered signs. All this indicates the need to check the cap of the expansion tank (2114 or another car) and replace it if it malfunctions.

Verification procedure

It is not so easy to check the operation of the reservoir cap, since it is necessary to create pressure, which is difficult. In service centers, special devices with a pump and a pressure gauge are used for this. This allows you to set the exact actuation values ​​of the lid valves. Self-diagnosis can be carried out, only it is less accurate in relation to the result. However, the faulty part will be detected.

First you need to unscrew the cover on a cold engine and inspect it: are there cracks, chips, dents, ruptures of sealing elements, wear and other defects. If the result is positive, it is worth moving on to the next method, how to check the expansion tank cap. You just have to screw it on first.

Now you need to start the engine and wait until it warms up to operating temperature. Then you need to quietly begin to unscrew the lid. If you hear the sound of escaping air akin to unscrewing the cork from a soda bottle, then everything is in order - the part is in good order and holds pressure in the system. While the engine is still running, it is worth inspecting the thick hoses for indentation. If so, then one of the valves is not doing its job.

And how to check the cap of the expansion tank in a different way? You can also do this (preferably also on a cold engine): unscrew the cap, then squeeze some thick hose with your hand and then screw it into place. Now you can remove your hand and observe: the hose takes its original shape - everything is in order, otherwise it is better to replace the cap. Only this method can not always be used due to the design features power unit different cars and hose locations.

Outcome

It is worth paying attention not only to the expansion tank itself, but also to its cap. Periodically evaluate her condition so that serious consequences can be avoided. Also, do not ignore the maintenance of the car in relation to the cooling system. That is, control the level of coolant in the tank, topping it up if necessary. And change antifreeze in time, which will allow you to enjoy trips in your car.

Any driver needs not only to know how to check the expansion tank cap, but to understand its principle of operation. This will teach you to be more responsible vehicle and save the family budget.

The role of the engine cooling system is difficult to overestimate. It is believed that the most important parts of this system are the pump and the radiator. But is it really so? For example, what secrets does the usual small cap on the neck of the expansion tank hide?

What is an expansion tank cap

To tell the truth, few drivers give great attention such a part of your car as the cap on the expansion tank. 90% of car owners believe that the cover acts as a locking device, that is, it simply prevents the coolant from splashing while driving. However, this is the opinion of amateurs.

The tank lid is indeed a locking device, but this is not its only function. Inside the cover there are two valves that stabilize the pressure in the cooling system and protect the engine from high temperatures.

The lid fits snugly to the edge of the tank, due to which conditions are created for the complete sealing of the cooling system

Device and functions

So, the cover in its composition contains the following elements:

housing made of hard plastic alloys;

rubberized gasket that acts as a seal;

two valves, one of which lowers the high pressure in the system, and the other raises, if necessary.

Included in lids different models cars can include from one to three springs

In fact, the cap of the expansion tank is a pressure control sensor. After all, when the engine warms up, the temperature of the coolant also rises, and therefore its volume increases. The more antifreeze or antifreeze warms up, the higher the pressure in the cooling system. At peak temperatures, the amount of coolant can increase by 20% due to expansion. Of course, under such loads, both the tank itself and the pipes suitable for it can burst. To prevent this from happening, a safety valve is built into the tank lid, which gradually relieves excess pressure.

The second valve is called the vacuum valve, since its main task is to increase the pressure in the system. He works primarily in winter time year, when the car is parked overnight in open areas. During parking, the coolant cools quickly and begins to decrease in volume. Accordingly, the pressure in the system drops rapidly. When the driver starts the engine, antifreeze cannot cool it well. To stabilize the pressure of the coolant, a vacuum valve mechanism is installed in the reservoir cap.

If the lid has lost its tightness, it can fly out of the neck of the tank under the influence of high pressure

That is, the expansion tank cap on cars works "in both directions" - it can both lower and increase pressure. Despite its apparent simplicity, the cover does the job of paramount importance and, one might say, protects the hoses and the radiator from damage.

How the coolant reservoir cap works

The cooling system of the internal combustion engine is completely sealed. However, due to the fact that the coolant is made on the basis of methyl alcohol, it can increase in volume during the heating process.

Therefore, excess liquid, as well as compressed air, enters when heated into reserve capacity- expansion tank. If the air in the system is highly compressed due to an increase in the volume of liquid, then the Exhaust valve in the lid: it opens slightly, and excess air comes out.

Next, when the machine for a long time stands, the reverse reaction occurs: the motor and the liquid cool down, due to which the volume of antifreeze is sharply reduced. Accordingly, air jams appear in the system. Thanks to the inlet valve, these plugs are quickly removed from the system.

The valves in the cover maintain the necessary pressure in the system

How to check the operation of the valves

Self-checking the cap of the expansion tank is difficult because without a special device it is impossible to know whether there is pressure in the system or not. Therefore, service centers use instruments equipped with a pump and a pressure gauge, which give an accurate assessment of the performance of the cover and each valve individually.

To diagnose the tank cap, a special device is used, which includes a pump and a pressure gauge

However, there is an easy way to check the reservoir cap:

On a cold engine, unscrew the cap from the reservoir neck.

Inspect the product from all sides: for cracks, dents, chips, breaks.

If there is no mechanical damage, then screw the cover back on.

With the engine running, carefully unscrew the cap.

At some point, gases should escape from under it - this indicates that the valve mechanism is in good condition.

Assess the condition of the connected hoses. If they are severely deformed, crumpled or swollen, then the pressure relief valve is definitely not working.

When checking, it is important to slowly open the cap, as the coolant can escape from the reservoir under high pressure.

By completing these simple steps, you can determine whether the valves on the tank cap are working or not.

Malfunction symptoms

The failure of the high pressure valve is usually accompanied by the fact that coolant begins to be ejected from the system even at normal pressure. Or, with strong heating of the antifreeze, pressure does not bleed. The driver can notice this problem by puffs of steam from under the hood. While driving, the engine starts to warm up, the temperature of the coolant also rises. Emissions of antifreeze enter the intake manifold, which causes it to quickly evaporate the liquid.

If the problem lies in the vacuum valve, then completely different signs of a malfunction will be observed. Air locks occur in the pipes of the cooling system, since the valve does not equalize the pressure. Because of this, failures may occur in the operation of the motor, since the low pressure of the coolant does not allow the cylinders to move correctly. In this case, the first symptom of this malfunction is hot motor And cold air from the oven at the same time.

Another symptom of a malfunction of the expansion tank cap are hose ruptures or tearing of pipe clamps. In addition, due to the destabilization of the internal pressure, all connections of the hoses and pipes of the system may fail. Therefore, at the first sign of expansion (indentation) of the hoses, you should immediately change the cap of the expansion tank on the car.

Pipe deformation is clear sign expansion tank cap failure

Do-it-yourself expansion tank cap repair

Repair work on the tank lid is so simple that even a child can do it. This is due to the fact that the cover design itself is simplified to a minimum. So, in order to repair the cover and valves in it, you must perform the following steps:

Unscrew the cap from the neck of the tank.

Pry off the rubber seal inside the cover with a flat screwdriver and remove.

Under it is a small valve device - you need to pry it with a screwdriver and pull it out. Nearby is the second valve - it is pulled out following the example of the first.

After that, clean out all the dirt that has accumulated in the lid. It is best to use ordinary soap solution and cotton swabs.

Screw the cap onto the neck of the tank and check the tightness of the system after warming up the engine.

After cleaning and installing the elements, the cover must perform its functions in full

What are the consequences of a defective lid

As mentioned above, the cap on the expansion tank is designed to stabilize the pressure of the coolant in the system. Accordingly, if the valve mechanism does not work, there will be no bleeding of excess pressure - this threatens to rupture both the hoses and the radiator. In rare cases, due to the high pressure of antifreeze, the tank itself gives a crack.

Low pressure in the system is dangerous because air pockets form. Because of them, the motor is not cooled to the right extent and may boil.

Therefore, the condition of the cap of the expansion tank must be checked periodically. Driving practice shows that replacing the cap every two or three years completely eliminates the occurrence of problems with the valves.

The most serious consequence of a tank cap failure is engine overheating.

The driver of any car needs to know about the purpose and functions of such a small element of the cooling system as the expansion tank cap. Engine cooling jokes never end well, so better times buy in two years new cover than to install a radiator or new pipes due to breaks.

Typically, the cooling system creates normal conditions for engine operation. The system coolant is stored in the expansion tank. The operation of the engine and other vehicle components often depends on the condition of such a part as the expansion tank cap of the VAZ 2114.

A bad cap can cause overheating and radiator failure, cooling fan and water pump failure, fan belt breaks, thermostat malfunctions, coolant leaks, and serious damage engine due to overheating.

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Functions

The expansion tank cap has two functions:

• shut-off;
• regulating pressure.

The locking function, as with all covers, is performed to avoid splashing of the coolant and to ensure the tightness of the cooling system.

The pressure regulating function is related to pressure differences in the expansion tank and the prevention of malfunctions and malfunctions.

Device and principle of operation

Structurally, the cover is a locking element, which is equipped with two valves. The first valve is used to reduce pressure, the second - to supply atmospheric air and increase pressure in the tank. The principle of operation of the cover is associated with changes in the density of the coolant when it is heated and cooled.

When the engine starts, the antifreeze heats up and its bulk density increases to 20-25%. Hot antifreeze warms up the air space. The exhaust valve sensor is triggered, it opens, part of the air leaves the tank and the pressure returns to normal. The bleeding process is periodically repeated when the internal pressure of the system exceeds 1.1-1.5 atmospheres.

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After turning off the engine, the antifreeze cools down, the pressure in the cooling system drops. When it drops below a critical level, the inlet valve opens and the system is supplied with atmospheric air. The pressure in the system equalizes and the inlet valve closes.

Symptoms

The most critical signs of a bad cap are steam from under the hood (if the engine temperature is not in the red sector, 90% chance that the problem is in the cap) and / or swelling of the expansion tank.

You can also make an assumption about the malfunction of the cover, if any:

• coolant leaks from the reservoir;
• antifreeze leaks at joints;
• gusts and swelling of hoses;
• air jams;
• engine overheating.

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Steam, boiling liquid and leaks are associated with wrong work exhaust valve. Air locks are usually caused by a malfunctioning intake or vacuum valve. Bursting (bulging) hoses can be caused by failures of both the exhaust and intake valves.

Air ingress creates air pockets inside the heater core, thermostat, and radiator hoses. As a result, the engine will start to overheat because the cooling system is not able to maintain a constant temperature.

If there are air pockets, you need to completely drain old fluid and fill with new antifreeze. new liquid pour gradually, in small portions of 100 ml.

If there is reason that the cover may be faulty, how to check the cover of the expansion tank VAZ 2114?

In service centers, the check is performed on special stands with a pump and a pressure gauge. The cover is screwed to the rack and the pump starts to supply air. When the pressure gauge reaches 1.5-1.7 atmospheres, the exhaust valve should work. The operation of the intake valve is checked in the same way, only the air is pumped out from under the cover. If the valves do not work, the plug of the expansion tank VAZ 2114 is faulty.

How can the cap be tested in the field?

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First you need to carry out visual inspection. Chips, cracks, gaps and other surface damage are grounds for replacement of the part.
Look at the pressure rating listed for the vehicle and compare it to the pressure rating listed on the part. If they do not match, replace the cover.

Visually inspect the condition of the main seal, pressure seal and back seal. Replace part if seals are cracked, hardened, or damaged.

Both the bleed valve and the vacuum relief valve should be easily pulled up and back out by the spring when they are released. If there is binding, replace the part.

The operation of the exhaust valve is checked by running engine. You need to wait a few minutes after starting the engine until it warms up.

The cooling system will start to work and the pressure in the expansion tank should change. Unscrew the plug of the expansion tank. If you hear a light pop, as when opening a bottle of sparkling water, this is a sign of increased pressure in the cooling system and a working exhaust valve. If there was no cotton, the exhaust valve is defective.

Usually the intake valve is checked on a cold engine. One of the hoses leading from the tank to the radiator is pinched by hand. After the hose is released, it should slowly equalize in thickness. If the hose does not line up, the inlet valve is faulty.

Always check the radiator and expansion tank when replacing a defective cap. It is possible that a malfunction has led to a dangerous build-up of excess pressure and damage or cracks have appeared.

Refinement of the new cover

Unfortunately, the quality of spare parts for domestic cars leaves much to be desired, and it is better to test the new cover on the stand. If the pressure does not hold or the excess pressure does not bleed, you can cut the springs. To do this, the part is disassembled, sealing gum pry off and remove with a screwdriver. Then the inner cover is carefully removed with a screwdriver and the springs are removed.

The large spring is cut one turn and the small spring two turns. As a result, the exhaust valve will begin to open at a pressure of 1 atmosphere, and not 1.7 atmospheres. The inlet valve must be free to blow when checking.

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Preventive measures

To prevent problems, replace the cover every 2-3 years. You also need to control the level of coolant and the pressure in the expansion tank of the VAZ 2114. Constant topping up of antifreeze prevents the occurrence of system overloads. Planned replacement antifreeze within the time recommended by the manufacturer, contributes to the safety of all elements of the cooling system.

Useful video

Additional useful information you can learn from the video below: