Contents: Reference ⇊ Reference ⇊
Which car owner, even those who rarely look under the hood, has not at least once poured this amber liquid into the engine of their favorite? Who has not at least once looked at the multi-colored canisters on the shelves of auto shops? Which oil to choose, what do all these inscriptions and brands mean? How convenient and simple it was before, here is "Zhiguli" oil, and here is for everything else. And now...
Why can't we, say, make one oil for all cars so that the motorist doesn't have to suffer?
Unfortunately, this is not the case, at least today, although the properties of motor oils have improved so much in recent years that it is practically impossible to make a gross mistake when choosing one. And yet, the operating conditions of oil in hot and cold weather, in a gasoline engine and a diesel engine, and even with a turbocharger, are too different. And everywhere, oil is required to reliably separate rubbing surfaces, preventing metal-to-metal contact, wash away the smallest particles of wear and carbon formation, prevent corrosion, remove heat, wash away varnish-like deposits, not oxidize, not foam, not thicken too much in the cold and not thin too much at high temperatures, not form sediments and, finally, not change all these qualities much over time. For this purpose, a whole complex of additives is introduced into the oil: detergents, antifoams, depressants (so that it doesn't thicken in the cold), anti-wear, etc. Some additives combine several functions, for example, barium dialkyl dithiophosphate is simultaneously an anti-wear, anti-corrosion and cleaning additive.
In the USSR, GOST 17479.1-85 was in effect and continues to be in effect today, defining the properties and marking of oils for piston automobile engines. Depending on the performance characteristics, six groups of oils have been established according to the degree of boost and the type of engines for which these oils are intended.
Group A - for non-boosted, B - for low-boosted, B - for medium-boosted and G - for high-boosted engines. In addition, there is also group D - only for highly-powered diesel engines and E - also for diesel engines, but stationary and marine ones, running on fuel with a high sulfur content. In addition, oils of groups B, V and G are further subdivided into carburetor with index 1 and diesel (index 2). The absence of an index indicates that the oil is suitable for both diesel and gasoline engines, but of course, this group according to the degree of forcing.
Another indicator that forms the basis of the domestic classification is the viscosity of the oil in centistokes (cSt) at an operating temperature taken as 100°C.
In order for the oil to easily start the engine in cold weather and at the same time maintain its viscosity during operation, thickening additives are added to it - polyisobutylenes. These are long molecular chains that tend to form balls at low temperatures. In this state, they have almost no effect on the viscosity of the oil; it remains quite liquid. As the temperature rises, the balls of molecules "unwind" and thicken the oil, increasing its viscosity. This is how all-season grades of oils are obtained, which have the index "z" in their designation.
So, here is an example of decoding the domestic designation: M12G - motor oil with a viscosity of approximately 12 cSt at 100°C of group G, that is, for highly accelerated gasoline and diesel engines. Is it summer or winter? And in general, what is winter and summer when talking about oils? It is generally accepted that winter is when the average air temperature is generally below 5°C, and summer is above 20°C. In addition, if the car is operated in difficult conditions (mountainous terrain, sandy and dirt roads), high viscosity oil should be used. M12G is a summer variety. In winter, it is preferable to use M8G oil. Although it must be said that most motorists have long preferred all-season oils M53/10G1 or M63/10G1 to these brands. This marking means that this oil has a viscosity of 10 cSt at 100°C, and behaves like a winter oil with a viscosity of 5 or 6 cSt in the cold. The letter "z" means thickened, not winter, as many people think. Oil M53/10G1 is more liquid, it is suitable for use in the middle zone and northern regions throughout the year. Oil U163/12G1 is more suitable for warm regions, as it is more viscous.
Our classification, despite all its informativeness, is rather cumbersome, difficult to pronounce, and most importantly, it is not entirely clear what a low-, medium- and high-powered engine is.
Today, two types of motor oil designations are accepted worldwide: by performance properties (API) and by viscosity (SAE).
The first type of classification was proposed by the American Petroleum Institute and looks like a combination of two letters: S (service) for gasoline engines or C (commercial) for diesel engines with an additional letter indicating the degree of perfection of the oil. Moreover, this degree is expressed in a rather original way - through the years of production of the engines for which this oil is intended. So, SA is an oil without additives for the oldest engines; SB - for newer engines; SC - for cars produced in 1964-67; SD - for engines of 1968-72; SE - for cars produced since 1972; SF - since 1980. Of course, we are talking about foreign cars, modern Russian cars correspond to classes SE, SF. The last two classes - SG and SH - are intended for the newest cars. As you can see, there are still many letters left in the Latin alphabet, so there will be no problems with labeling when improving the properties of oils.
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The Society of Automotive Engineers (SAE) has proposed a classification by viscosity at 100°C. It looks like this: SAE 20, SAE 40, etc. If the oil is winter, its designation includes the letter "W". All-season oils are designated according to the same principle as domestic ones, only with a dash, for example: SAE 20W-50. Just remember that these numbers are not centistokes. For example, oil M63/14G1 corresponds to SAE 15W-40. The marking of all foreign oils contains, in addition to the name of the manufacturer, both types of designation, for example: Mobil SAE 10W-50 API SF. Sometimes the marking contains the words Super, Extra, Diesel, Turbo, Multigrade (all season) etc.
Mineral motor oil, that is, oil obtained from petroleum, has, as already noted, the following disadvantage - a strong dependence of viscosity on temperature. To reduce this phenomenon, thickening additives are introduced. But here's the problem: they deteriorate quite quickly due to high mechanical and thermal loads. This is especially noticeable on worn-out engines, where after a run of several hundred kilometers on new all-season oil, the emergency red light suddenly comes on again. What to do? Switch to a thicker summer one? But it's winter outside, you won't be able to start the engine in the morning. The solution is to use synthetic oil.
They are obtained by chemical synthesis, which achieves high homogeneity and stability of properties. But the most important thing is that the viscosity of "synthetics" changes little with temperature, that is, it is more liquid in the cold and thicker in the heat than "mineral water". This property will reduce wear of parts and friction losses, which saves fuel - about 2-3%. In addition, "synthetics" burn less in the engine and generally lasts longer, forming few deposits. It is easy to distinguish synthetic oil by the inscription "synthetic", as well as by a wide temperature range: 5W-40, 10W-60, etc. The only bad thing is the high price, approximately 2.5-5 times more than mineral oil. Therefore, there is a compromise - semi-synthetic oils, that is, a mixture of "synthetics" with mineral (tactile 50/50). It should be noted that you should not make such a mixture yourself, as mineral oil additives may not dissolve in synthetic oil. As a result, "clots" form in the oil channels.
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As for mixing two mineral or two synthetic oils, that's fine. And do not believe the various instructions that prohibit mixing oils from different companies. Modern oil must undergo homologation, that is, approval for use, and one of the points of this procedure is a certificate of full compatibility. And really, can you imagine an American car owner who had to constantly remember what kind of oil was in his car? When mixing different domestic oils, you can use the formula:
X = Ay + B (1 - y),
where X is the viscosity of the mixture, A and B are the viscosities of the mixed oils, and y is the proportion of the first oil in the mixture.
A few words about the choice of oil depending on the engine condition: During the break-in period, it intensively removes wear products from friction pairs and therefore it should not be thick. SAE 20, SAE 30 are best suited here, and from all-season SAE 20W-30, 10W-30, 5W-30. During the "maturity" period, SAE 30, 20W-30, 15W-30, 10W-40 are suitable for VAZ engines. It is better not to use thicker ones yet due to the risk of oil starvation in the cold season. But the UZAM and MeMZ-968 engines need something thicker, since the former has larger gaps and worse oil scraper rings, and the Zaporozhets has high thermal stress. Use here SAE 20W-40, 10W-50, 10W-60. These same oils are also suitable for any "old" engines.
Should the engine be flushed when changing the oil? If the car has always been running on high-quality oil, then no, but at least once every two years or every 30,000 km it is still worth flushing the engine. Moreover, there are now compounds on sale that turn old oil into flushing oil. You don't have to pour and fill several times, as before, and the entire rinsing procedure will take you 5-15 minutes.