Sorry for so many posts, but one more is on my mind. I have a 1990 Bonnie SSE, and I have heard that Rotella 15w40 was a great oil to use on higher mileage cars (I belive it was in a Caddi Forum on the 4.9, 1990 model) and was wondering if any of you have used this in your car and what you thought. I know I will need to change my oil next month, thought I would get a jump on it. Thanks.

on the 3800 stick with 5w30 or 10w30 any thicker wont help unless you have an internal problem with the engine, and cause more harm than good.

Rotella is a very high quality oil, mostly used in diesel engines. I agree about the weight recommendations for our cars. If it ain't broke...

Fix it until it breaks!

I agree with all of the above. If you're changing your oil sometime next month, go with 10W-30 and nothing heavier than that.
Dino Oil


is OK in my book too.

Yeah. It'* good diesel oil (what we use in the old F250) but modern gas engines, like our 3800s, need generally thinner stuff.

I run either 10-40 or 15-40 in my car during the summer months, there'* nothing wrong with running thicker oil ESPECIALLY in a high mileage motor.

Just don't run that thick of oil in the winter months if you get down below freezing temps....because then the poor oil pump'* trying to suck a golf ball through a straw....LOL

Diesel oil is a good choice for high mileage engines. It has more detergents and more anti-wear additives. The 15w40 may be a little thick for a 3800 but this can be thinned out by mixing it with some 10w30. I prefer Delo and Chevron supreme for their more potent add-pack. Try and find a UOA that beats this one.

I would not run 15w40 in any cold climate. They also make 10w30 HDEO but it is harder to find.

During the winter I run the factory required or suggested oil.

Summer time I run Rotella - T 15/40 All summer long.