i have been running 10w30 in my rebuilt 400 and was wondering for summer months if i should switch to something heavier like 10w40 or something. i always use valvoline, but what weight?

 

I'd look at what kind of oil pressure you are getting with the 10w30. If it is in spec you should be OK. Maybe could run a heavier oil, say a 15w40 in the summer (particularly in Texas). My '95 300 cid is running 10w40 year round. With 5w30 the oil pressure was below spec, though only by 4 psi.

 

A lot depends on where you live, how you drive and what temperatures you expect.

When I lived in So Calif, where the temps went between maybe 30 and up to 110, I usually used 5W30 Synthetic, or a 20W50 dino, depending on which engine. My "good" car got syn, my beater Datsun got dino.

I prefer to stick with one grade/weight oil for all weather if the range is adequate. Superstition and some magazine reading I guess.

If you lived in warm climate I would probably go with a 20W50 since it works fine down to maybe freezing. I would like to say use a 10W40 or 15W40, but I am still nervous about those weights, too large viscosity range in a light base oil, probably just old habit and old technology.

Assuming the problem with too much viscosity range has been fixed in the newer 15W40, that is probably what I would use year round unless I expected lots of 120+ temperatures, then I would definitely use 20W50.

Course, since I have used syn in almost everything since 1980, I no longer worry about temperature extremes and just use 5W30 or 10W30 syn.

Just my opinion,

Jim Henderson

 

Years ago I ran 10 W 40 in a 74 Wagon with the 400 engine. Put a lot of highway miles with no problems.