at 75-80 degrees outside, or 175-180 degrees engine temp, is 15-40 thicker then straight 30? im considering switching to rotella t rather then vavoline 30. i have a 460 in a 78 150, and it gets run hard. any recommendations?

 

Those are very moderate temps, so 40 is probably not necessary. What are your hot oil pressures? IMO, Rotella T has a much more robust additive pack than Valvoline 30. Rotella T is available in straight 30 here in SoCal, but maybe not in your area.

Jim

 

anything is better than valvoline period valvoline is the bottom of the oil chain they put very little in their oil and it thins out way too fast if you have a walmart near by they are now selling 10w30 rotella t i just bought 3 gallons it will kepp your engine spotless because it is a diesel oil i have been using it and love it

 

Your oil temps will almost mirror your coolant temps. The ambient air temp is pretty much irrelavant except in extremes. If the engine is at temp, the oil is as thin as a 40w at temp. If I had a 460 and run it hard, I would be using Delo 400+ in 15w-40 just to insure things stayed clean.

 

I'm with gashog on the Valvoline oil......my truck appeared to break it down fast. Much happier with the 15w40.