Dear Car Talk

Dear Car Talk | Sep 01, 2009

Dear Tom and Ray:

My sister and I recently had an argument. She drives only short distances, rarely more than five miles. She wants her '98 Buick Regal with 40,000 miles to last as long as possible. Therefore, she refused to drive the 350 miles to visit for the holidays. I believe that an occasional long drive actually extends the life of the car. Which one of us is correct, and why?

-- Bill

RAY: Well, I think she just didn't want to visit you, Bill. Do you have a houseful of bratty kids or a neglected cat box or something?

TOM: She certainly wouldn't ruin the car by putting another 700 miles (round trip) on it. After all, that's what cars are designed to do: Drive places. But is it GOOD for the car? Not really.

RAY: In the old days, when cars had carburetors, and excess fuel poured into the cylinders, taking a long, high-speed ride could help burn off some of the carbon deposits that tended to build up on the pistons. But fuel injection meters the fuel so precisely on modern cars that carbon deposits rarely are a problem.

TOM: The only problem with repeated short drives now is moisture. When the engine runs, one of the byproducts of combustion is water. That water is sent out the tailpipe. But if you drive only a few miles, the exhaust system and muffler never get hot enough to vaporize that water. That makes the exhaust system rust prematurely.

RAY: So your sister may drive up to the pumps and say, "Fill her up, check the oil and change the muffler!"

TOM: But you don't need to drive 350 miles to heat up your exhaust system. Five or 10 miles will do it, depending on the weather. And, in any case, a long trip once a year is not going to help keep your muffler from rusting anyway, if it's staying moist the other 364 days.

RAY: So there's no real advantage for her car in making this trip. In fact, the opposite is true. There's a pretty direct correlation between the number of miles driven and the end of a car's life. So in general, the fewer miles a car is driven, the longer it lasts.

TOM: So forget about the car, Bill. Send your sister a plane ticket for Christmas next year. But if she starts chirping about all the potential wear and tear on the airplane, give up.

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