Dear Tom and Ray:

I have a 1992 Ford F150 with a V8 engine. I get really bad mileage. How bad is bad? On a good day I get six mpg in town. I don't take it on the highway much, so I can't give you an accurate figure on that. I don't "hot rod" it, and I take good care of the beast. The dealership couldn't find any problems with it. They checked the oxygen sensor and all of the various computers. They said, "Tough luck; live with it." I have a buddy who told me to try high-performance spark plugs and an air filter. He said I would definitely see the difference. What do you think? -- Mike

Tom: The biggest difference you'll see is in your bank balance, Mike. So save your money.

Ray: This may be one of those situations in which the mechanic at the dealership is using a high-tech approach and overlooking the simple stuff. His scanner may tell him that your sensors and computer are operating properly, but it won't tell him if you have something as simple as a stuck thermostat.

Tom: A thermostat that's stuck open could make a huge dent in your mileage. When the thermostat is stuck in the open position, the engine is, in effect, being "over cooled" all the time. That means it never gets up to proper operating temperature. And if it's running too cool, the gasoline won't combust properly, and your mileage will stink (as will your tailpipe).

Ray: That's why everyone's mileage is worse in the winter. And an engine temperature problem affects a fuel-injected vehicle (like yours) much more than it affects an older, carbureted car.

Tom: You need a old geezer to take a look at this for you, Mike; a guy who was around before engines were dominated by computers. Look for a guy with white stubble and no teeth, if possible. When you come across a guy who whistles through his gums and says "Yessshh, Shhonny, shhhtep right in," he's your man!

Don't get stuck with a lemon. Be an informed shopper. Read Tom and Ray's guide "How to Buy a Great Used Car: Secrets Only Your Mechanic Knows." To order, send (check or money order) to Ruin, P.O. Box 536475, Orlando, FL 32853-6475. You can also order online.

© 1997 by Tom and Ray Magliozzi and Doug Berman Distributed by King Features Syndicate, Inc.

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