Am I doing any damage if I use "small engine" motor oil on a big engine?

Dear Car Talk

Dear Car Talk | Mar 01, 1995

Dear Tom and Ray:

I have a 1975 Buick LeSabre with a 350 V8. I use Castrol motor oil. What does Castrol mean when it says made "for smaller engines?" Am I doing anything wrong by using it on a big engine?

RAY: Not to worry, Arthur. Back in 1975, when everybody drove big cars, Castrol was engineered for big engines. Later on, when people turned to small cars, suddenly Castrol was engineered for smaller engines.

TOM: What does it mean? Probably not much. What they say is that smaller engines run hotter. And because they run hotter, they need a better quality oil. So, if their advertising is to be believed, an oil that's good enough for a small engine would be MORE than good enough for a steamship powerplant like you've got in that Buick. So in that case, you're fine.

RAY: And if you don't believe their advertising, then you'd conclude that Castrol is just the same as every other motor oil. In which case you're also fine. So you're covered either way, Arthur.

Get the Car Talk Newsletter