As promised, I "smoked" a little on the Internet about adding 2T of oil. I started with foreign forums.

So, the story goes back to around 2007, which coincided with the application of new standards for diesel fuel, which reduced the sulfur content up to its complete removal.

Euro 2 since 1996 sulfur content - 0.05%
Euro-3 since 2000 sulfur content - 0.035
Euro-4 since 2005 sulfur content - 0.005
Euro 5 from 2010 sulfur content - 0.001

Petrochemists discovered back in the early 90s that a decrease in sulfur levels affects the deterioration of the lubricating qualities of the fuel and in 1993 a new requirement was introduced by the standard: the lubricating property of diesel fuel, tested on a high-frequency piston unit using the metal ball sliding method (), the maximum allowable wear was fixed at level 460 µm. Standard - ISO 12156-1 (and Russian version -).

Axiom one- a decrease in the level of sulfur content worsens the lubricating properties of the fuel, which in turn directly affect the wear of the fuel equipment.

But the progress and work of petrochemists did not stand still, and this natural lubricating agent (sulfur) was replaced with special additives (one of the options is long chains of carboxylic acids), which were designed to replace the lubricating properties of sulfur.
One of the leading developers of these additives is the German company BASF.

It should also not be forgotten that engine building did not stand still at that time and engines were developed to operate with low sulfur fuel.

Axiom two - the reduction in sulfur content, which impairs the lubricity of the fuel, has been replaced by the addition of special lubricant additives.

But everything new is accepted with hostility, no one believed the chemists, society decided that the new standards were detrimental to diesel technology, and then some schemer had the idea to add two-stroke oil to the fuel in small proportions to make up for the loss of the miraculous effect of sulfur. Dieselists liked the idea so much that it simply blew up the Internet. There were no scientific confirmations and tests to confirm this idea; information was transferred from one car owner to another according to the OBS principle.

It is worth noting that the "benefit" was observed for old mechanical diesel engines, especially vehemently 2T oil or as they call it 2SO (two stroke oil) was used by American diesel drivers riding large pickup trucks. Many people note noise reduction, cleaner exhaust, smoother engine operation. All reviews are subjective and rather based on the placebo effect, which is noted in the messages of car owners.
The proportion of adding 2T of oil to the fuel is recommended at the level: 1 part of 2T of oil to 200 parts of fuel. Given the slightly higher density of 2t oil relative to the density of diesel (especially winter), the use of this method requires good mixing of oil with fuel, which is simply impossible to do by simply adding it to the tank.

As for the harm from using 2T oil. There is no unequivocal answer here, since the dose of adding 2T oil is homeopathic and the potential harm from its use is extended over time and in the end, even if some problems appear, they are written off as temporary wear of the engine and fuel equipment, but in no way to add oil.

Users of new diesel engines with electronic injection (in particular Common Rail) are wary of this "technology" and not many are willing to participate in the experiment for their money, but the crowd effect has an impact and still some succumb. This also applies to owners of particulate filters.

Axiom three - neither the benefit nor the harm from the use of 2T oil by adding to diesel fuel has been scientifically and practically proven.

In conclusion, we managed to find one interesting post that justifies at least, if not harm, then the uselessness of using 2T oil:

Completely useless not only for HDi diesel engines, but also for any Common Rail engines, an event. And that's why:

To begin with, why add oil to diesel fuel at all? The explanation is simple (and well known to any diesel specialist (a specialist in deed, not in words)) - the diesel “rings”, “rumbles”, “stinks” and runs unevenly with a heavily worn injection pump and other components and parts of the fuel equipment - the gaps have increased, the settings are "gone", painstaking (and expensive) adjustment and / or replacement of worn components and parts (also not cheap) is required - and the toad is tormenting, oh how tormenting. ...

And then a technique proven by generations of unscrupulous sellers of diesel cars comes to the rescue - two-stroke oil is poured into the fuel. ... The viscosity of the fuel inevitably increases, which means that worn-out plunger pairs and / or spools / rotors “float” and stop “ringing”, it is more difficult for a worn high-pressure fuel pump to inject viscous fuel, moreover, most likely through uncleaned nozzles, which means the amount the fuel entering the chambers decreases, as does the injection start point (towards the “after” TDC), the fuel starts to burn more slowly ... and there is an illusory effect that the engine starts to run smoother and quieter. Like new... That's what the "two-stroke oil scam" is all about - MIRACLES!

But, as you know, miracles, alas, do not happen! And all this event is countered by at least the fact that when the diesel engine was new, it also didn’t “ring” at all, it also worked quietly, and carried the car forward like a young bun .... on a regular one, without any additives fuel!
So why does he now require topping up of oil in order to work (more precisely, create an illusion) also quietly and measuredly? ... So it makes perfect sense that the engine is Worn out. And this is treated only by repair.

Do not engage in "garage experiments"! Any professional diesel mechanic will tell you that a normal and serviceable, healthy and well-groomed diesel engine, even with half a million mileage, runs quietly, pulls confidently and "breathes" measuredly on a regular normal diesel engine, WITHOUT adding all sorts of miraculous substances to the fuel ..

All of the above applies mainly to diesel engines with a "classic" injection system, now extinct, like dinosaurs once ...

But what about Common Rail?

And for Common Rail, this event is absolutely useless due to the fact that in the direct injection system of diesel engines ... there are no gaps (!), Or their presence is minimal.

Imagine yourself as a particle of fuel that has entered the fuel tank from a filling nozzle and trace the path of this particle to the combustion chamber of a diesel engine with a Common Rail system ...

First, we are floating in the tank, sucked in through an interestingly shaped fuel intake nozzle. Its shape is due to the effect of "tea leaves in a glass", whereby, as a result of the swirling of the fuel flow, large particles of dirt, due to centrifugal force, accumulate away from the fuel inlet, or "fly" past it, remaining in the tank. The oil in the fuel is useless at this stage. ...

Next, we meet with the fiber of the coarse filter, the purpose of which is to prevent large particles of dirt and sand from penetrating into the fuel line. ... We swim through the fiber and swim-float-float along the fuel line.
Here we also have oil "like pliers in a bath" ...

Next, we flop into the fine filter, through the filter element, which traps microscopic particles of debris at a level close to the molecular one. Here, the fuel is freed from water particles that remain in the filter chamber. In the fine filter, the fuel flow is also freed from possible air bubbles. Oil here is also "neither to the village, nor to the city." ...

The first mechanism that we can meet is a low pressure fuel priming pump. It is usually made in the form of a turbine, an impeller, but more often, in the form of an eccentric ... The task of this pump is to supply a particle of fuel to the high pressure pump. Here, in the fuel priming pump, the pumping element usually does not require lubrication with the fuel itself, since it usually does not come into contact with anything, and if it does, it rubs against anything, then the density of this contact is minimal - there is practically no wear here - it is vanishingly small. In the small chamber of the fuel priming pump, the fuel is finally freed from air bubbles. As you can see, oil is also "away" here ...

We get into the high pressure fuel pump. Here, probably, there will be friction? ... But no! And here it is minimal! The fact is that high-pressure pumps of Common Rail systems have the simplest piston design, due to the simplest and only purpose - to create and maintain high pressure in the ramp (receiver) of the system. Moreover, the pressure control is not controlled by the pump itself, but by its valves. For example, HDi diesel high-pressure pumps from Bosch have a three-piston radial design with short stroke pistons. The friction against the cylinder walls is minimal here, the speed of the pistons is also minimal, and the seal is created by "floating" bimetallic rings. By the way, the pistons and cylinders themselves have a ceramic-metal coating of friction surfaces, which also contributes to minimal friction and wear. By and large, this is NOT even a plunger pair ...

It is in the high-pressure fuel pump of injection systems of the "classic" type that the plunger pairs have an ultra-precise design, the movement of parts occurs both in length and in angle. Moreover, this happens at a constantly changing pressure from zero to high. The movement of the piston relative to the cylinder in the plunger pair has a high speed and a large, constantly changing stroke ... respectively, and high wear. And there is also the effect of cavitation (which, by the way, "finished off" pump-injector diesel engines, now almost extinct ...) ...

Therefore, the oil in the fuel for the Common Rail high pressure pump cannot in any way have any noticeable effect on the properties of rubbing surfaces and wear (which is practically absent).

We sail further ... After the high pressure pump, we find ourselves in a ramp. For a particle of fuel, it's all the same if a person suddenly finds himself in a cyclopean-sized tank, in which there is one inlet and four (for a four-cylinder engine) outlets to the injectors. There may also be a fifth hole through which the valve that regulates the pressure in the rail bleeds excess fuel into the "return".

We float inside the nozzle through a thin capillary. We linger for a moment in a small chamber near the needle. And we fly headlong into the combustion chamber through the thin holes of the atomizer of the nozzle directly into the hell of air heated to a thousand degrees ... in which a particle of fuel instantly burns out ...

Common Rail injectors are fundamentally different from the "classic" ones in that they are opened by electronics, and not by fuel pressure. They have a compact, even rather miniature, and relatively simple design, almost like conventional injection gasoline engines. The fuel in them practically does not come into contact with the pushing element.

In "classic" injectors opened by fuel pressure, the pushing element interacts directly and is washed (and lubricated) with fuel. The design itself is very complex, and as a result, the "classic" nozzle is much larger in size. The friction and wear of the pushing element is here "in full".
But we have Common Rail ...

The fact that the pushing element, needle, etc. in Common Rail injectors, they experience dozens (or maybe hundreds!) of times less loads, including frictional ones, practically and in fact do not require lubrication and therefore almost do not come into contact with the fuel flow (they do not need it), relative to diesel engine injectors with a "classic" type injection system, the following figures illustrate...

Shown here are Bosch common rail injectors (widely used on HDi diesel engines) ...
On the left - a nozzle with an electromagnetic pushing element, on the right - with a piezoelectric...

The capillary for fuel supply is highlighted in red. The pushing element, its rod, and other moving parts (the number of which is minimal, and they are practically absent in the piezoelectric nozzle) have an "eternal" supply of heat-resistant synthetic lubricant and an anti-friction coating of friction surfaces, designed for the entire life of the nozzle ...

Below is a diagram of a diesel engine injector with a "classic" type injection system ...
As you can see, its device is more complex and "rougher" than that of Common Rail, and the entire pushing element, friction in its parts, is in the full power of the fuel ... The nozzle itself requires careful adjustment, and all this despite the fact that in the diagram ...
far from the most complex design of the "classic" type injector ...

And this is a diagram of a diesel engine injector with a "pump-injector" injection system ...

As they say - feel the difference ... Extremely complicated (in some ways even to the point of absurdity), unreliable and cumbersome design finally "sentenced" the injection systems of this scheme, which are now completely supplanted by Common Rail ...

There are also good visual examples of oil getting into a CR type fuel system:

CONCLUSION. The benefits of using 2T oil are based solely on faith, so the appropriateness of its use is determined by the user's belief in the effect of this method.