The Sherlock Holmes School of Auto Repair:

Dear Car Talk

Dear Car Talk | Aug 01, 1991

Dear Tom and Ray:

I have a '79 Honda Prelude that started making a loud noise over 35 mph. My mechanic told me I needed a new exhaust manifold. Since I don't know much about cars, I let them fix it and it cost me a bundle. Now I still have the same exact noise and it's getting worse. I brought it back and this time they told me for sure that the noise is a wheel bearing. Do you think the mechanic is right this time? Please help!

RAY: Your mechanic obviously didn't go to the Sherlock Holmes school of auto repair, Nikki. Both the exhaust manifold and a wheel bearing can make the kind of noise you describe, but a little investigation could have told him which one it was.

TOM: A bad exhaust manifold will make noise whether or not the car is moving--the higher the speed of the engine, the louder the noise. So if the exhaust manifold was the problem, your mechanic should have been able to rev the car and make the noise for you right there in the garage.

RAY: A bad wheel bearing, on the other hand, will only make noise when the car is moving. So if it was the wheel bearing, he'd be hard pressed to make the noise for you by revving the engine. One more test, like putting the car on the lift and spinning each wheel with the engine off, could have confirmed the diagnosis.

TOM: My guess is that when you go and ask for your money back, he's going to try to convince you that you needed that new manifold anyway. But since the noise hasn't changed at all, I doubt that's true. If he's a decent guy, he'll either give you your money back for the manifold, or at the very least, replace the wheel bearing for free.

RAY: If he refuses, go to another mechanic and have the wheel bearing taken care of. It could be dangerous. Wheel bearings hold the wheels on, and it would take Jackie Mason to explain how you park one of these Preludes with one wheel tucked underneath the car.

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