Are you running an xxW-40 ?

[xx78]

I use Rotella T6 5w40 in my 2002 Land Rover Discovery. So for so good.

 

[CIRHS]

5w60 Penrite 10 tenths Premium - in my Commodore SS 6L V8 GM L77 Engine, 2001 Fireblade .929L In-line 4, Ford XR6T Turbo 4L In-line 6. Best oil Ive ever used so far.

 

[marco246]

See my sig. . . . Just so happens I'm using the grade of oil specified by the manufacturer for each car-except for the Alfa, which specs 20W-40.

 

[SS1970chrysler]

My '70 Newport, '66 Newport, and '66 300 all with 383's are running 15w-40 and doing just fine. My '62 Buick is currently on 30w, sometimes 15w-40 and '48 Packard is on 30w. '77 Riviera is on 20w-50.