Is thicker oil a benefit as engines age?

“I have a 93 Buick Roadmaster with a Chevy 5.7l Lo5 v-8 engine. The engine has 60,000 miles on it. The previous owner didn't drive her all that much here in Florida (see low miles for a 1993), but really didn't service her either. After flushing the tranny with Mobil 1™ Synthetic ATF and the rear end with Mobil 1™ Synthetic Gear Lube LS 75W-90. I did a few quick oil changes with Mobil 1™ 5W-30. All is well. The car runs better than new. After talking to my friend (an experienced engine builder), he said to try Mobil 1™ 0W-40 in her; that this combo would work well in my car. Something about poor (or lack of) service history of my engine. And sometimes as engines add more miles, a little thicker oil works wonders. Well, in went 0W-40. Maybe it's just me, but my engine seems to like it. Smooth, maybe even more power. Hard to believe. I feel I'm getting just as good mileage or better with this thicker oil. So since there is no warranty to worry about, is this acceptable? What do you think?”

Matthew Decker, Delray Beach, Florida

Answer

We think Mobil 1™ 0W-40 is an excellent choice. It provides the viscometrics of an SAE 40 oil at operating temperature. In Florida’s high ambient temperatures, a high viscosity oil can help reduce oil burn-off. You probably do not take advantage of the 0W cold start performance living in Florida, but since you are happy with the overall performance, we would say you should keep on doing what you are doing.