Dear Tom and Ray:

Since installing a new 350 cubic-inch engine in my 1973 Chevy G20 Van, I have been using Mobil 1 synthetic oil. It says I can wait 15,000 miles between oil changes, but I change it every 5,000 miles. Will this prolong the life of my engine? Am I wasting my money by paying $4 a quart and changing my oil so often, or will my engine last forever? -- Bob

RAY: Well, let's look at the best-case scenario, Bob. Let's say your engine lasts forever. What are you going to do with the engine when the rest of the 1973 Chevy Van is a 6-inch pile of orange rust?

TOM: Right. It's kind of like worrying about the curtains on the Titanic. Your van is pushing 30 years old, Bob. That's great, but you certainly can't expect it to last forever. So why put all that extra money into making its engine last forever?

RAY: Even if you live in an area of the country where cars don't rust, parts just wear out or break after a while. And you'll find (if you haven't already) that it gets harder and harder to get parts for a car this old.

TOM: So unless you're committed (pun intended) to rebuilding and restoring the rest of this van as it falls apart and have another vehicle to drive while you're searching far and wide for parts, I'd throttle back on the oil changes. With the synthetic oil and a vehicle this old, 15,000 miles should be more than adequate.

RAY: And then you can put the savings toward a nice set of curtains for the windows, Bob. Good luck.