quality and viscosity
You often hear that modern oils are by definition better than old ones. Therefore, they can be used in all engines without any restrictions. It is, only many confuse the oil grade with viscosity.
Today’s most modern motor oils are of SP grade – they replace obsolete oils, for example, SM or SN groups. But this has nothing to do with the SAE viscosity rating of oils. And low viscosity oils like 0W-20, recommended for most modern engines, don’t need to be poured into older engines.
Low viscosity oils have a more watery consistency than lubricant, which confuses seasoned drivers. How is this possible in the engine? However, car manufacturers recommend using low viscosity oils in modern engines. But for engines of the old design, they are not suitable.
How do you recognize low viscosity oil?
We are used to using the SAE oil viscosity rating. The numbers after W in the designation indicate the range of viscosity changes at engine operating temperature (at 100 aboutFROM). The higher the numbers, the higher the viscosity.
In addition, there is the HTHS parameter, which describes the high temperature viscosity of the oil. This is not the known kinematic, but dynamic viscosity, measured at 150 aboutC. It characterizes the resistance that must be overcome when attempting to move one layer of oil relative to another.
This parameter is measured in millipascals per second (mPac) – it indicates the energy-saving properties of engine oil, as well as the bearing capacity of the oil film.
HTHS is not marked on jerry cans: in fact, this parameter is already included in the engine oil specification itself:
Relationship between HTHS parameters and SAE oil specifications
|
HTHS<3.5 |
HTHS>3.5 |
HTHS>3.7 |
|
xW-8/12/16 |
xW-30 |
15W/20W/25W-40 |
|
xW-20 |
0W/5W/10W-40 |
xW-50 |
|
xW-30 |
|
xW-60 |
Which oil protects the engine better?
The lower the HTHS, the lower the friction loss and thus the better the energy savings (lower emissions and fuel consumption). And the higher the HTHS, the stronger the oil film. It turns out that full viscosity oils protect engines better than low viscosity ones?
This is not true!
If you pour full-viscosity oil into a modern engine, it won’t penetrate everywhere. After all, these units have smaller gaps between the work surfaces and narrower oil channels. And the lack of oil can seriously affect the engine. Therefore, in engines not older than three years and not lower than environmental class 4, it is usually recommended to top up with oils with a low viscosity.
But For structurally old engines with large gaps between parts, low viscosity oils are not required. The optimum oil wedge in the crankshaft bearings of these engines can only be created by high viscosity oils The lack of a sufficient film between the rubbing pairs in the cylinder-piston group will inevitably lead to the appearance of grooves and, as a result, to overhaul of the engine.
Low viscosity oil is not suitable for worn engines. All because of the same larger holes through which the oil will actually flow out without having a positive effect. And the oil pump will not be able to create the necessary pressure when the oil heats up.
What oil does my engine need?
An oil with an optimal HTHS classification is recommended for each engine. And the “more is better” principle doesn’t work here.
To select the right oil, you must strictly follow the manufacturer’s tolerances, which can be clarified in the service book or at an authorized dealer. And oil company websites usually have online pickers.
And experiments with oils — both high and low viscosity — can go sideways.
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