Q: I have a 1997 Ford Explorer with 93,000 miles on the odometer. When I drive it up steep hills, smoke comes from under the hood. I have taken the car to a mechanic, who could find nothing wrong, but this happens every time I drive up a steep hill. What do you think the problem is?

NANCY SCHROCK   
   San Rafael, California

A: Car problems that conceal themselves in the presence of mechanics and then, as soon as you’re on your own, gleefully reappear are the most frustrating kind. That the smoke comes from under the hood and only on steep hills suggests a small oil leak fairly high on the engine. The extra heat resulting from a climb may be generating seepage from, for example, the gasket between the valve cover and the cylinder head. When escaping oil contacts hot exhaust components, it turns to smoke. You’d expect to see some residue, but it’s possible the small amount of leaked oil simply blends with the oily grime already present and what reaches the exhaust system completely burns off, especially around the valve cover. (As you inspect, be sure to keep clear of the fan, which can start up even when the engine is off.) It may be that something relatively cheap as car repairs go, such as a new valve cover gasket, will cure the problem.

Q: Just a few months after I replaced my car’s alternator, the new one went bad and had to be replaced also. Can there be something about my car that ruins alternators?

STAN HUZAREWICZ   
Utica, New York

A: Probably not. Alternators usually need no external encouragement to fail. An alternator produces electricity that the engine and all the car’s electrical equipment, such as lights and CD player, depend on. Like any car component, an alternator can fail even when there has been no mistreatment. Unlike most replacement parts, however, many re- placement alternators are rebuilt rather than new. In our experience, even though key parts are swapped out and the units may be tested before delivery, their life spans vary widely and are unpredictable. One might churn on forever and another die in a week. There is very little your car can do to destroy an alternator.

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