The numbers are not telling the hole true .....
This part is taken from a well respected oil company
"Conventional multiple grade mineral and semi-synthetic motor oils, as 100% synthetic super-multigrade lubricants (5W40, 5W50, 10W60...) use additives to boost their viscosity. These viscosity additives tend to loose efficiency when submitted to extreme conditions, which translates into a drop of viscosity and oil pressure."
Their " line benefit from the natural viscosity of synthetic ester basestocks, they need very little of such additives, or none
The ASTM D 4741 official test of HT/HS* (High Temperature High Shear) viscosity measures the viscosity of lubricants at very high temperature (150°C / 302°F) and shear (1 000 000 s-1). This test is considered to be a good model of the fluid's state when exposed to extreme shear and temperature as found in an engine.
The higher the benchmark, the best the oil film keeps up its viscosity, hence its resistance to high stress in hydrodynamic rating. Tests prove the best results are achieved with a high viscosity grade (50 or 60) at high temperature, and without viscosity boosters.
- Resistance to high temperature coking
While racing, when the engine is pushed to the extreme, or during pit stops and refuellings, the oil temperature reaches maximal values.
Same happens to usual cars when stuck in traffic jams, hard or fast-driven for long journeys, or stopped at busy toll-gates.
Hence the capital attention to avoid the carbonization of lubricants heated to high temperatures.The lubricant residues carbonized through overheating (i.e. charring) are weighed, the best benchmark being a low weight.
The test measures the coking of engine oils at a sustained high temperature (5 days at 160°C / 320°F) and blasted for 48 hours against an aluminum shim heated at 290°C / 554°F.
Tests prove the choice of basestocks, especially synthetic ester bases, to be a major promoter of resistance to high temperature coking."