![]() But let’s try and select the best option based on a particular motor. So, it is clear there is no optimum universal recipe on how to choose oil for every type of engine. But right now the motor itself is more interesting and topical to us – where in what modes and which oil is more effective. This can be done using modern mathematical modeling techniques to present the friction processes that take place in the engine. And again, we have to look for an optimum. Friction power, which we are trying to minimize, grows in parallel with the viscosity in direct ratio. It is easy to think that if you want to hop up the motor, you should pour a thicker type of oil. This, however, concerns only engine power boosting. But the common correlation is universal – the faster the engine rotates (more exactly, the faster is the piston), the bigger is the optimum oil film thickness. Clearances are the most important factor defining the angles of attack that impact the lifting power. The thing is clearances change during engine life. More than that, it depends on the engine construction and the engine’s real condition. But this optimum thickness of the oil layer is unique for every engine operating condition. As a result, the effective engine power with the optimum thickness of the film will be maximum. That is, both a thinner and a thicker film will cause engine power loss. If this is the case, friction causes minimum power loss. There is a certain optimum oil layer thickness. Scientists measured films thickness and figured out how films behave in engine cylinders and the way oil viscosity impacts this behavior.īesides, they noticed a kind of funny correlation: engine power depends on oil layer thickness and oil viscosity, in particular. Several experiments almost simultaneously took place in many of the world’s leading countries, including the USA and Japan. As for piston rings, the presence of films under them was confirmed only in the 1980s. The viscous fluid is oil.īy the way, the appearance of films in bearings has always been evident. The angle of attack is shaped either by a round crankshaft bearing clearance, or is provided at a stage of production of the details by adjusting the required working surface profiles, and is tuned during the engine run-in. Speed is generated by crankshaft revolutions. The first one is speed – relative movement of surfaces, secondly, a particular ‘angle of attack’, and, finally, viscous fluid. To start, let’s find out how films appear and what influences their thickness. However, engine power, burning oil consumption and even the temperatures of the parts and, consequently, the overall engine reliability depend on oil viscosity. ![]() The higher viscosity is, the thicker oil films appearing on the engine’s moving parts are– in crankshaft bearings, under piston rings. That is, kinematic viscosity can vary by 10-15% within the acceptable range. For example, W30 oil viscosity can vary from 9.3 to 12.5 cSt (centistokes – viscosity measurement units) at 100☌ (212☏). ![]() The second digit defines oil viscosity at 100☌ (212☏), more properly, not the viscosity itself but the acceptable range of its variation. The first digit is the minimum below-freezing temperature at which the engine can be started. Letter W in between two digits is a sign of all-season oil. ![]()
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