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It is believed that without low-viscosity oil, a modern engine will eat a lot of gasoline, and it will smell bad from the exhaust pipe. But they say that for Russia everything should be different, including oil.
We took three fully synthetic imported motor oils with a viscosity of SAE 5W 30 from the leading manufacturers occupying the lion's share of the domestic market - ExxonMobil, Shell and Castrol. Not so widespread, but no less well-known Motul oil was added to this trinity.
How was it tested? On each of the oils, a specially prepared bench engine spun in the set modes for one hundred and twenty hours, while its characteristics were compared at different stages of testing. The motor is a domestic VAZ 21114 eight-valve with injection, with a modified control program and an oil cooling system for the pistons.
Why is the engine not foreign-made? Test conditions do not allow. The methodology requires opening the motor before and after testing, measuring, defecting, photographing and weighing the details. And modern non-suction motors cannot be disassembled - the crankshaft cannot be removed there. More precisely, you can remove it, but it is already forbidden to put it back.
After a fixed time, we took - three times - oil samples to assess the rate of aging. Tracked the change in physico-chemical characteristics of the oil, as well as the content of wear products in it. And the autopsy of the motor clarified the idea of deposits and wear.
To eliminate doubts about possible fakes, we gave fresh samples of oils to the laboratory to determine the basic physical and chemical parameters and compared them with the indicated manufacturers. If they match, then the oils are real, not fake. I was surprised by another: the initial parameters of all four oils are almost the same. Are they not from one barrel alone? From different! This was found out after measuring dynamic viscosity over the entire temperature range. But first, remember what viscosities are in general.
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KINEMATIC, DYNAMIC AND HTHS
There is a direct relationship between the viscosity of the oil, the friction loss and the wear rate of the friction assembly. In classical hydrodynamics, two characteristics of viscosity are distinguished - dynamic and kinematic. The dynamic viscosity of the oil is important for the motor, since it takes into account the change in density depending on temperature. And kinematic viscosity is important for oilers; it can be accurately determined by a capillary viscometer. Previously, the viscosity parameters prescribed by SAE class limited only the possible range of kinematic viscosity of the oil at a temperature of 100 ° C. This range for SAE 30 oils is 9.3–12.6 cSt; for SAE 40 oils it is wider than 12.6–16.3 cSt.
The SAE classification is now supplemented by dynamic viscosity limits at 150 ° C. This is the so-called high temperature viscosity HTHS (High-Temperature, High-Shear).
Previously, it was believed that the classification according to SAE was enough to select the oil, and then it turned out that it was not enough. Oils from one group at operating temperatures can vary in viscosity by tens of percent, and this is essential for the operation of the motor. Therefore, they introduced an additional restriction.
table-02The dynamics of the kinematic viscosity during the test reflects the rate of aging of the oil. This is one of the main rejection parameters of oil. The dynamics of the kinematic viscosity during the test reflects the rate of aging of the oil. This is one of the main rejection parameters of oil. Manufacturers of modern oils focus on opposite priorities. So, Shell declares low viscosity of Helix Ultra oil, which predetermines low friction losses. Motul specifically developed the 8100 X Clean FE, which claims a high HTHS value. Who is right?
For completeness, we will go through all temperatures - from winter cold start to fully operational modes, like a fully warmed motor. The highest HTHS viscosity at the first test was for Motul 8100 X clean FE, as promised by the manufacturer: 3.2 MPa · s versus 2.7 MPa · S for Mobil. Take-off - almost under 20%! This means that this oil will reduce the load on the bearing by 20% - or it will increase the pressure on the bearing by the same 20% without deteriorating its working conditions. The fee for this is the highest dynamic viscosity at low temperatures: 8330 MPa · s for Motul oil versus 6220 MPa · s for Mobil oil. So, in the Arctic and Antarctic, starting a motor with Motul oil will be more difficult.
table-03The content of wear products in the oil sample taken after the test cycle illustrates well the protective properties of the oil. The content of wear products in the oil sample taken after the test cycle illustrates well the protective properties of the oil. However, it is more interesting to trace the dynamics of changes in this parameter over the entire duration of the test. Oils Mobil 1 ESP Formula and Motul 8100 X clean FE for 120 hours of torture by the Russian engine and the Russian (not the best, as they say) fuel changed their parameters slightly and quite predictably. During the tests, the dynamic viscosity in the entire temperature range increased by only 3-5%.
But Castrol Edge FST and Shell Helix Ultra oils have changed their viscosity by 21–28%! Moreover, the increase in viscosity for Castrol oil began almost immediately - such a dynamics is not typical for the usual behavior of the oil. And Shell oil was doing well until the middle of the test, but surrendered in the second half of the cycle. As a result, by the end of the tests, the advantage that these oils had over viscosity at low temperatures over Motul oil had completely melted. Those planning to use these oils in harsh northern conditions have something to think about.
An even more expressive picture, reflecting the rate of aging of oils, is given by the analysis of the dynamics of changes in the kinematic viscosity at 100 ° C.
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And again: the viscosity of Motul oil remains virtually unchanged. Mobil oil has a more noticeable change in viscosity, and by the end of the test period it has reached a threshold value. But Castrol showed a very significant increase in viscosity at 100 ° C, far jumping out of tolerance. The most interesting thing is that the viscosity at 40 ° C by the end of the tests began to decrease - this can be seen from the data in the final table. The viscosity index flew as much as 210!
The viscosity index is an important parameter of engine oil, which characterizes the rate of change in viscosity with increasing temperature. The higher it is, the smaller the difference between viscosities at high temperature and at low. For complete synthetics, it usually lies in the range 160–180.
And another oddity is Castrol oil. Usually, the alkaline number gradually decreases: a complex of detergents is activated. And then on the contrary - growth!
It is possible that calcium or another element, to which the device reacts, is returned to the oil from deposits formed in the engine. By the way, for the remaining three oils the same method gave the expected result.
We evaluated the energy saving of oils twice, comparing the fuel consumption in the regimes of our cycle both with fresh oil and with the spent 120 hours. These results are also summarized in tables.
Here again, it is appropriate to return to the conversation about HTHS. The highest HTHS oil - Motul 8100 X clean FE - also showed the best result. However, all tested oils, judging by the results, may well be classified as energy-saving. But those whose viscosity growth rate is lower have least changed fuel consumption and engine power after a long test cycle. The effect of high-temperature viscosity was most evident when analyzing the protective functions of the oil. Analysis of the content of wear products in oil samples taken at the final stage of testing clearly reveals the unconditional leadership of high HTHS oils. This is Motul 8100 X clean FE. It is quite understandable: higher viscosity - more thickness of the separating layer and less wear of engine parts.
Opening the engine after the test cycles showed approximately the same final level of high and low temperature deposits, while more stable oils gave a slightly better result. But in general, all oils with these parameters showed a high result, characteristic of high-quality synthetics.
table-06High-temperature deposits on the lateral surfaces of the pistons left by modern synthetic oils should not exceed 1.5 points of the ELV scale. And did not go out. The ELV scale is a scale of expert assessments of the level of deposits: an absolutely clean piston - 0 points, black and dirty - 6 points. High-temperature deposits on the lateral surfaces of the pistons left by modern synthetic oils should not exceed 1.5 points of the ELV scale. And did not go out. The ELV scale is a scale of expert assessments of the level of deposits: an absolutely clean piston - 0 points, black and dirty - 6 points. High-temperature deposits on the lateral surfaces of the pistons left by modern synthetic oils should not exceed 1.5 points of the ELV scale. And did not go out. The ELV scale is a scale of expert assessments of the level of deposits: an absolutely clean piston - 0 points, black and dirty - 6 points. Related Materials Fatal motor oil disease
NOT FOR RUSSIA?
Why did oils perform differently during testing? Two of them - Motul 8100 X clean FE and Mobil 1 ESP Formula - worked without comment, and the other two showed not so optimistic results. The very nature of the aging of the oil, when the viscosity starts to go around, and other parameters as a whole remain normal, most often indicates that the polymer thickeners in the oil used in the additive package conflict with something.
Coming up with this examination, we wanted to continue the theme of “oil plague” that we raised three years ago - unpredictable oil decomposition, which produces black tar in the channels of the lubrication system, oil pan, and valve mechanism. This disease has killed more than one hundred motors. And the oilers as one of the possible culprits of this disaster called Russian gasoline. Then we found other causes of the "plague", moreover, confirmed by experiment. But it was necessary to check the version about the influence of bad gasoline.
The solution was found after our examination of cheap 95 x gasolines (ЗР, 2015, No. 5), during which it turned out that most of them contain banned methanol. This is the kind of gasoline we used for our tests
table-07The tested synthetics produced relatively thin layers (in general, of a similar thickness) of low-temperature deposits. The tested synthetics produced relatively thin layers (in general, of a similar thickness) of low-temperature deposits. Thus, our studies have confirmed that bad gasoline is really able to spoil the oil, and with it the engine. Yes, but after all Motul 8100 X clean FE and Mobil 1 ESP Formula oils, working on the same gasoline, did not express any complaints against him! This means that the additive package can be adjusted in such a way that in our conditions the oil works normally. Another thing is that not everyone succeeds.
In the meantime, we repeat: go around a wide range of unverified gas stations! Regarding the choice of engine oil, we recommend that products with a higher HTHS value be preferred.
The motor, nerves and wallet will be more whole!
How was rated
Our results are relative, applicable only to a comparison of the four tested synthetics. When comparing the motor characteristics of the engine, another oil was included in the test - a relatively simple anonymous semisynthetics of the same viscosity class, taken as a basis for comparison. Bench tests completely eliminate the uncertainty that is unavoidable when testing on a real motor under normal operating conditions. In the latter case, a lot depends on the engine operating conditions, its technical condition, driving style, fuel quality, weather overboard and a number of random factors.
The applied technique allows us to evaluate the comparative quality of engine oil according to the characteristics that are usually taken into account when they are approved for use by various car manufacturers. We list these signs.
Energy saving is determined by changing the average specific fuel consumption when working on test oil in comparison with the base.
Wear protection is determined by changing the mass of the control parts (liners of the crankshaft bearings and piston rings), changing the size of the parts, and the content of wear products in the engine oil sample taken after the tests.
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The tendency to form high-temperature deposits is determined by a visual assessment of the level of contamination of the side surfaces of the pistons. The tendency to form low-temperature deposits is determined by the change in the mass of the control weight elements - engine parts installed in the valve cover (oil separator mesh) and in the oil pan (oil filter pick-up fungus).
Environmental indicators are determined by the change in the toxicity of the exhaust gases during engine operation according to the standard test cycle on the test oil compared to the base.
In addition, the comparative aging rate of motor oil and its effect on engine performance were evaluated. Resource indicators of oil were characterized by the dynamics of changes in its viscosity, alkaline and acid numbers, and a change in dispersing ability.
As the rejection parameters, on the basis of which the preservation of the oil’s working capacity was evaluated, the viscosity limits determined by its SAE class were used. For SAE 5W 30 class oil: kinematic viscosity measured at a temperature of 100 ° C should be in the range of 9.3-12.6 cSt. In addition, the oil was rejected if at some stage of the test its alkaline number fell by more than 50% of the initial value.
High temperature oil viscosity
In modern engines, the oil temperature in the working area can reach 180–200 ° C, especially in a friction pair, the piston ring - the engine cylinder. The viscosity of oils of even one group according to SAE at such temperatures can vary significantly. Thus, our previous examinations showed that for oils of the “magpies” group at 150 ° C the kinematic viscosity can vary in the range of 5.4–6.8 cSt, that is, the run-up reaches 25%! For the “thirty” the relative difference may be even greater.
That is why, since 2001, the concept of high-temperature viscosity HTHS has appeared in the SAE J300 rules. This is the dynamic viscosity of the oil, determined on a rotational viscometer under fixed conditions - at a shear rate of 106 1 / s.
Manufacturers of modern oils have the same goal - optimizing engine performance, but they choose mutually exclusive methods to achieve it. So, for example, in the description of Shell Helix Ultra oil it is said that due to its low viscosity it reduces friction losses. Motul has specifically developed 8100 X clean FE with high HTHS.
Who is right? We turn to the theory. Any friction pair in the engine is a kind of bearing: cylindrical, if it is a crankshaft bearing, or flat (slider), if it is, say, a friction pair of a piston ring - a cylinder. So, one of the most important indicators of the quality of the bearing is the load factor. It is defined as the ratio of the average load on the bearing to the working viscosity of the oil, multiplied by the shear rate, and all this is multiplied by the square of the ratio of the size of the working gap to the diameter of the bearing. The value of the coefficient of loading should lie within certain limits. Exceeding entails a sharp increase in the rate of wear and friction losses, but too low a load factor leads to an increase in friction losses.
The load and speed in the bearing are operational parameters, we don’t touch them. If we reduce HTHS, then automatically increase the bearing load. And we can compensate for this only with the size of the working gap - it must be reduced. But there is a limit! So, for each motor, with its design features and operating modes, there is its own optimal high-temperature viscosity HTHS.
Moreover, even in the case of a single motor, each of its operating modes will have its own optimal HTHS. And the law is simple - the higher the load, the higher the viscosity should be.