Re: Use The Right Oil
Silkolene PRO S 10w-50 is a shear stable race synthetic oil made of 100% true synthetic basestocks (PAO 80% Ester 20%) with no petroleum oils in it.
It's an oil that will stay in grade far longer than many others because the basestocks need little or no VI Improvers so there is no where for the oil to shear back to.
The differences between 10w-50 and 10w-60 are as follows:
The SAE band for 50 is 16.3 Centistokes (cSt) to <21.9 at 100C. For SAE 60 it is 21.9 to < 26.1 (It is interesting to note that some xW/60 oils also qualify as SAE 140 gear oils: the SAE 140 range is 24.0 to <41.0 at 100C).
Typically, 10W/50 oils have a 100C viscosity of 18cSt; 10W/60 grades are usually around 23.5cSt. But the question is, where do they stand after a few thousand miles hard use? Because of the greater amounts of VI improver polymer needed to ‘lift’ the viscosity, a 10W/60 is more prone to shear effects, so it can be expected to drop to around 19 or 20cSt; a really good quality 10W/50 such as Pro-S will only drop to about 17cSt.
Sheared-down 10W/60 is actually better for the engine! Modern designs do not need very high viscosity oils. They can cause trouble with air entrainment, and cavitation inside bearings at high RPM. (So the Silkolene 10W/60 is not particularly close to 10W/60 when both are new.