WIll leaving my car in "overdrive" damage my engine?

Dear Car Talk

Dear Car Talk | Sep 01, 1996

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.

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