Everything you need to know about car and motorcycle oils

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SAE viscosity :

W = Winter the number to the left of W- indicates the cold viscosity, the lower it is, the more fluid the oil is at start-up and the rapid lubrication.

The number to the right of W- indicates the viscosity (or thickness) of the oil when hot (at 100°) which corresponds approximately to the temperature reigning along the cylinder/piston assemblies and which is very high on the surface of the oil. friction.

Cold, a 0w oil and more fluid than a 5w oil
When hot, a W-30 oil is more fluid than a W-40 oil.

0w30 oil, the smoothest when cold and hot, great fuel savings

0w40 oil, the most fluid when cold and more viscous when hot than an SAE 0w30 oil

5w30 oil oil viscosity commonly used on modern engines provides fuel economy with the w30 grade

5w40 oil the standard oil on many engines in circulation

10w60 oil for extreme engines

10w40 oil no longer used currently because these oils are obsolete

An obvious example of cold starting a thin oil compared to more viscous oils:

To the SAE viscosity is added the viscosity HTHS at 150° . HTHS viscosity (from English: High Temperature, High Shear) is a measurement of the residual oil film under high stress (mechanical pressure) at 150°.
The HTHS viscosity allows us to better understand the "solidity" of the oil in areas with high stress such as camshafts, pushers and crankshaft bearings.
This makes it possible to realistically judge the behavior of the oil at 150° when two surfaces press with very high pressure, which was not the case for SAE viscosity.
We now have High HTHS oils (>3.5 mPa.s) and Low HTHS oils (<3.5 mPa.s)

High protection oils are “High HTHS”
Oils that are more geared towards fuel economy are “Low HTHS”

The ACEA standard (defined by European manufacturers):

The A corresponds to gasoline engines and the B corresponds to diesel engines. All current oils are gasoline/diesel compatible (including turbos)

ACEA A3/B4 (or A3/B3/B4): the most commonly used engine oil for both gasoline and diesel engines (including of course turbo-diesels)

ACEA C3 : also provides protection for particle filters (or FAP, DPF) by limiting in particular harmful and destructive discharges from FAP such as sulfated ash and phosphorus.

ACEA C4 : the same advantages as ACEA C3 but specific to certain DCI engines such as Renault Nissan. Oil must be used if requested by the manufacturer

ACEA C2 : the same advantages as ACEA C3 while providing fuel savings. Oil to be used only if requested by the manufacturer

ACEA C1 : the same advantages as ACEA C3 while providing fuel savings. Oil to be used only if requested by the manufacturer

SAE viscosity history:

The first standard to appear at the beginning of the 20th century is the SAE viscosity which made it possible to classify oils according to their fluidity.

At that time, engine oils were monograde, which means that they had a viscosity grade of 100° for summer, for example SAE 50 or SAE 40, knowing that the lower the number, the more fluid the oil.

For a very long time one oil was used in summer SAE 40 or 50 and another in winter SAE 20W the W meaning Winter

Multigrade oils appeared in the 1950s and from then on both Winter and Summer viscosities were found in the same product, for example 20w-50.

Standards for engine and transmission oils:

From 1920 the API (American Pretroleum Institute) standards became established by establishing classifications linked to the performance of engine and transmission oils.

For engines, standards for gasoline engines have appeared
API SA, SB up to API SN to date.

And for Diesel these are the standards starting with a C:
API CA up to API CF

But the American API standards are no longer suitable for European and Asian engines, it is the ACEA standards which are now taken into account because they are much more adapted to our engines. For transmissions, API standards are still used in Europe.

The origin of the oils:

Synthetic Oil: increasingly used for their advantages. The synthesis bases can be Polyalphaolefin (PAO) Esters or even hydro-cracked bases (HC)

Semi-synthetic oil: which does not mean that it is a mixture with 50% synthetic oil, 10% synthetic oil is enough to have this name for these less and less used oils

Mineral oil almost no longer used

Vegetable: castor oil used since antiquity and still capable of lubricating 2T and 4T competition engines running at very high speeds of 16000 rpm like 100cm3 karts!