HTHS - Bob Is The Oil Guy: "A jump in HTHS by about +1.5 results in approximately 1/5 the wear. Now this relationship is not linear and flattens as one nears a 40+ weight oil."
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"Summary: It was found that HTHS correlates better with wear values found in actual oil analysis and actual tear-down measurements than does measuring the oil film thickness in situ."
The HTHS (high temperature high shear) viscosity of a given oil is a very important consideration in my choosing a motor oil. Yes, Porsche has a minimum HTHS that is aligned with the levels required for an ACEA A3/B3 lubricant, but M1 0w40 just meets that specification. There are many 0w40 and 5w40 lubricants that have up to 25% higher HTHS #s.
The oils we've seen with some of the highest quoted HTHS viscosities have been Mobil 1 V-Twin 20w50, Amsoil Harley V-Twin 20w50, and Brad Penn Racing 1 20w50, all with HTHS #s near or in excess of 6.0.
It is also worth mentioning that in one of the quoted SAE journals, that the zero wear intercept for HTHS viscosity was a HTHS of 13.7, so most definately there is improvement when going from 3.5 on up to even 6.0 IMHO.
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