Get out your stethoscope to get to the bottom of noises

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 noise 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 this screeching noise 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.

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.

A Easiest fix: Start and run the engine for 20 minutes every few days. Cheapest fix: Install an inexpensive battery master switch. Granted, shutting off the master switch after driving will lose all the various presets, but at least the car will start a week later.

Why is the charging system operating at 14.5 volts and higher? With a fully charged good battery and normal electrical load, I'd expect to see voltage in the 13.5-to-14.5 range. The higher voltage may mean a bigger demand on the system, or some type of overcharging problem.

Typically, parasitic draw with everything turned off is less than 15 to 30 milliamps. Draining a battery down to roughly 40 percent of its reserve capacity will result in a no-start scenario. Here's the example from the Alldata database: "A vehicle with a 30-milliamp drain and a fully charged 70 RC battery will last 23 days. But if that battery is at only 65 percent of full charge (green dot barely visible), it is going to last only 15 days before causing a no-start." If you drive only short trips every six to 10 days, the battery may not stay fully charged.