Dear Tom and Ray:

I recently bought a Pontiac Bonneville with Overdrive. I'm getting more confused all the time about the use of the Overdrive feature. Prior to my Bonneville, I had a 1984 Chevy Caprice, and I drove in overdrive all the time, just like you recommend. However, when I bought the Bonneville, the salesman said I would probably damage the engine if I did that with this car. Is my salesman right? -- Marilyn

Tom: Your salesman apparently has been breathing too many exhaust fumes, Marilyn. Leaving the car in Overdrive won't damage the engine.

Ray: There are a couple of situations where you don't want to be in Overdrive. One is when you're descending a long, steep hill. In that situation, you want to downshift from fourth gear (Overdrive) to third and use the engine's natural braking power to keep the car at a moderate speed. That keeps you from having to overuse your brakes -- which could overheat them and lead to brake failure.

Tom: In fact, on particularly steep hills, you might need to downshift to second or even first gear to keep from having to ride the brakes.

Ray: The other situation where you MIGHT not want to be in overdrive is when your transmission is "hunting." You'll know your transmission is hunting when it's wearing an orange vest and carrying a rifle.

Tom: Actually, "hunting" is when the transmission isn't sure whether to be in third gear or Overdrive, so it "hunts" back and forth between the two. It tends to happen when you're driving continuously in the 35-45 mph range, or traveling over rolling hills.

Ray: Hunting is not terrible for the car, but it can be annoying to the driver. So if it bothers you, turn off Overdrive until your driving conditions return to normal.

Tom: But in general, our advice stands. For the vast majority of drivers, driving conditions and cars, people with automatic transmissions can just leave the car in Overdrive all the time and forget about it.

Changing your oil is the cheapest insurance you can buy for your car, but how often should you change it? Find out by ordering Tom and Ray's pamphlet Ten Ways You May Be Ruining Your Car Without Even Knowing It! To order, send (check or money order) to Ruin, P.O. Box 536475, Orlando, FL 32853-6475. You can also order online.

© 1996 by Tom and Ray Magliozzi and Doug Berman Distributed by King Features Syndicate, Inc.

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