[donstevens]

Mike,

Don't be such a puss. As an oil guru you should be the first to experiment in your own car and pass on your experience to others. Besides, if you asked someone else to experiment because you pussed out and they had an engine failure, just think about how you would feel?

I have used Amsoil 15W40 in my old SC and it worked fine. I lost track of that car after it had well over 200,000 miles and had never been torn down. It was a hot running motha too. It did run cooler on the 15W40 vs mineral 20W50.

I am running Amsoil 20W50 in my car now and it actually runs hotter than it did on Mobil-1 15W50. Mobil-1 is typically on the thin side of the viscosity range as well where Amsoil is typically on the thick side. So, your experience with "thinner is cooler" seems to have a parallel to mine, at least in this one case.

I agree with your statements that one cannot deduce cooler operating temperature between synthetic an mineral oil of the same viscosity primarily because of viscosity range. According to CTC lab results 50 weights fall between 16.3 and 21.9 cSt. So a 16.3 cSt mineral will most likely run cooler than a 21.9 cSt synthetic. It may be a coincidence that ..P experienced cooler temps with the synthetic but there are too many factors that affect oil temperature, regardless of oil composition, to draw a blanket conclusion that all synthetics run cooler than a mineral oil of equivalent viscosity. Having said that, historic data shows that the synthetic oil will have more stable thermal properties at temperature extremes over time than the mineral oil but that is a different story.

I question you comment about "The synthetic oil actaully will pull them out of the rubber matrix leaving behind mico fissures for oil to seep out of. " Is that still true today? For all oil belnders? I thought they were over thise issues with modern synthetic oils. If not, wouldn't every car leak? Why would anybody use them?

Don