Dear Car Talk:
I have a great 2000 Cadillac DeVille with 95,000 miles. It burns some oil. Can I change over to a synthetic oil now? Would that help with the oil burning? Thanks. -- John
You certainly can switch to synthetic oil, John, but it probably won't help with the oil burning. It might have helped if you'd switched 85,000 miles ago.
You don't say how much oil this great Cadillac is burning, but since you took the trouble to write to us, I'm guessing "a lot."
The "Northstar" engine they used in these cars is known for burning oil. So the question is: How much are you burning? Are you burning so much that your car is enveloped in voluminous clouds of blue smoke whenever you stop at a traffic light? Are little old ladies flipping you the bird as they pass you because your oil cloud is obscuring their view of the road? If that's the case, you're probably burning a quart every few hundred miles. That suggests that something is wrong deep inside the engine -- most likely bad rings.
But if you're burning a quart every 1,000 miles or more, you're probably better off just trying to keep it from getting worse quickly.
Here are a few suggestions on how to do that: First, keep a close eye on the oil level. Oil burning usually gets worse over time. So if you're used to checking it once a month and finding that it's a quart low, start checking it twice a month. Otherwise, one day you're going to do your monthly check, and find it's down 2 quarts. And running the engine low on oil will only exacerbate the oil burning.
Second, change the oil regularly. We've noticed that when some of our customers have cars that burn oil, they stop doing their oil changes. They figure, "Hey, I put in 4 new quarts over the past few months, so it's already got all new oil!"
But it doesn't work that way. A lot of the old oil is still in there, and it's trying to hold contaminants in suspension -- until it gets so dirty that it can't hold them in suspension anymore. So your oil still needs to be changed.
And finally, you can consider switching to a slightly more-viscous oil. Using a thicker, molasses-like 20W-50 concoction used to be the go-to solution for old oil-burners. But with newer technology, I'd be cautious about switching viscosities. In fact, you really should check with your dealer's service manager first. Your engine probably calls for 5W-30. And you might be able to go to a 10W-30, for instance, and see if it changes your burn rate at all.
But because engines are so sophisticated now, and were designed and engineered for certain oils, gone are the days when you could just throw some 50-weight gear oil or Brylcreem in there and hope for the best. So concentrate on our first two suggestions, John. Keep the oil topped up between changes, and change it regularly.
And based on your mileage, you're only driving about 5,600 miles a year, so maybe you can tough it out for another 10 years or so. Just don't look in the rearview mirror.