Q: I have a 2006 Mercury Mountaineer with a 4.6-liter V8 that makes a screeching noise along with a tapping noise upon a cold start. I removed the serpentine belt and started the engine, and the same thing happens. When the engine is warm, the tapping noise is not noticeable but the screech is less but still noticeable. The tapping is probably the exhaust manifold leaking. Is the combination a result of a bad exhaust manifold, or would the screech be something else?
A: You didn't mention whether the engine still runs well, delivering good performance and fuel economy. If so, I don't see how the screeching could be a potentially catastrophic metal-on-metal scenario. You've taken the correct first step - start and run the engine for a few moments with the serpentine belt removed. This eliminates the A/C compressor, alternator, water pump, power steering pump and any other belt-driven ancillaries as the culprit.
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The tapping noise may be a leaking exhaust manifold, as you suspect, or a loose spark plug, but my Alldata automotive database pulled up bulletin 06-9-11, dated May 2006, describing a loud tapping noise in this engine because of a stuck or collapsed hydraulic-valve lifter.
Use a mechanic's stethoscope - or a long wooden or metal rod - to try to locate the noise. Start the engine and place the stethoscope against the valve covers, cylinder head, block, etc., to try to pinpoint the sound.
I'd get to the bottom of these noises before putting too many more miles on the vehicle.
Q: My 2002 Ford Focus lost its blower motor. The difference between the cost of an original unit from Ford and one from an auto store is $25. Is there any difference between the units? Would buying the Ford part be a better deal?
A: Having spent my life doing my best to save money on motor vehicles, this is a no-brainer. Why buy the most expensive new part for a 10-year-old vehicle? Buy the aftermarket blower. It may well be the same unit, but even if it not quite the quality of the Ford part, it doesn't have to last another 10 years.
Paul Brand, author of "How to Repair Your Car," is an automotive troubleshooter, driving instructor and former race-car driver. Email questions to paulbrand@startribune.com. Please explain the problem in detail and include a daytime phone number.