quote:Originally posted by Clockwork:
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One last question (which I know is an unanswerable question as I've read the battles before)..........Does 10w40 in the cooler months and 15w-50, 5w-50 or maybe 20w-50 in the peak of summer sound like a good plan? The motor's mods as far as I know include just a slightly lumpier cam and an aluminum intake.
This is answerable when you decode the viscosity grade numbers. Remember that the first number (with the W) is the cold temperature performance, and the second number is the operating temperature performance.
Say it to yourself like this: 10W-40 "behaves like" a straight SAE grade 10 at low temperature, and a straight SAE 40 at operating temperature. That is where the term "multigrade" comes into play. It behaves like two different SAE oil grades across a broad temperature range. In tribology lingo, the multigrade oils have a higher viscosity index than straight grades.
If you had a California car, where the cold start temperature rarely would be below 32*F, then a 20W-50 would be sufficient. I'm a big fan of film strength especially on flat tappet cams so 50 would be the operating temperature regardless. If you really want the best of both worlds for cold starts in the Wyoming winter, then 5W-50 would be the kind, with one caveat. Really broad temperature range performance like that usually use viscosity improvers that can shear down over time reducing the 50 rating, so more frequent changes might be in order. I have a feeling specialty car owners change oil much more often than necessary anyway.