JSharp,
I've run the Amsoil 10w-30 and 20w-50 synthetics in my Audi 100 under the same conditions. I have factory installed, "VDO" oil temp and oil pressure gauges in this vehicle. The 20w-50 runs about 15F-20F hotter in the summer w/ the AC on and running @ 80 mph; compared to the 10w-30. Fuel efficiency also drops by about 3% with the thicker oil ....Since the 20w-50 runs much hotter - oil pressure is NOT that much better than with the 10w-30. In that sense, running a heavier oil is a catch 22 type of situation. This is something that few people understand and appreciate! It's what Terry Dyson alludes to all the time, if you're paying attention.
As you well know, more viscous liquids have poorer heat transfer properties, and also generate more "intrafluid" friction. The best analogy to explain intrafluid friction to a laymen, is to think of the energy needed to stir a glass of honey as opposed to a glass of water. In a similar fashion, the extra energy needed to pump and shear/deform a heavier oil between moving parts goes directly into heating the fluid. This merely wastes fuel and causes the engine to run hotter. Additionally, thermal expansion of the Al pistons in the cylinders reduces available power. Finally, significantly hotter engine oil temps reduce the expected life of all your elastomeric seals and gaskets.
For optimum engine performance and engine life, you want to run the THINNEST oil that will give you acceptable oil pressure, under the worse case, high heat, high load conditions. If oil pressure is acceptable, then valvetrain wear will also be acceptable by default ....Minimizing valvetrain wear is really more a matter of having the optimum additive chemistry and not just a thicker oil.
Sometimes getting folks to understand these things is like pulling teeth ...
TS
I've run the Amsoil 10w-30 and 20w-50 synthetics in my Audi 100 under the same conditions. I have factory installed, "VDO" oil temp and oil pressure gauges in this vehicle. The 20w-50 runs about 15F-20F hotter in the summer w/ the AC on and running @ 80 mph; compared to the 10w-30. Fuel efficiency also drops by about 3% with the thicker oil ....Since the 20w-50 runs much hotter - oil pressure is NOT that much better than with the 10w-30. In that sense, running a heavier oil is a catch 22 type of situation. This is something that few people understand and appreciate! It's what Terry Dyson alludes to all the time, if you're paying attention.
As you well know, more viscous liquids have poorer heat transfer properties, and also generate more "intrafluid" friction. The best analogy to explain intrafluid friction to a laymen, is to think of the energy needed to stir a glass of honey as opposed to a glass of water. In a similar fashion, the extra energy needed to pump and shear/deform a heavier oil between moving parts goes directly into heating the fluid. This merely wastes fuel and causes the engine to run hotter. Additionally, thermal expansion of the Al pistons in the cylinders reduces available power. Finally, significantly hotter engine oil temps reduce the expected life of all your elastomeric seals and gaskets.
For optimum engine performance and engine life, you want to run the THINNEST oil that will give you acceptable oil pressure, under the worse case, high heat, high load conditions. If oil pressure is acceptable, then valvetrain wear will also be acceptable by default ....Minimizing valvetrain wear is really more a matter of having the optimum additive chemistry and not just a thicker oil.
Sometimes getting folks to understand these things is like pulling teeth ...
TS
