QDear Tom and Ray:

My '92 Honda Civic has had a "hole in the muffler" sound for about a month, and my husband says it's fine to drive it that way. We need this car to go on a family visit (about 1,100 miles round trip). Are there any long-term hazards (to the car or to our health) to driving with a "holey" muffler? Personally, I suspect that my husband just doesn't want to spend the money, because it took two summers of driving around in central Virginia heat and humidity before I threatened to wreck the car and buy a new one if he didn't get the air conditioner fixed. I was pregnant with twins the second summer, and they were born in early July. He waited until late summer to deal with the A/C problem!

-- Diane

ARAY: Your husband is obviously one of my brother's soulmates. I feel your pain.

TOM: Actually, this is dangerous. To you, your family and the car.

RAY: Any hole in the exhaust system reduces the back pressure in the cylinders. The closer to the front of the car the hole is, the more the back pressure is reduced. And without sufficient back pressure, the exhaust passes by the valves faster, which makes the valves run hot. If they run hot enough, they can melt. And that'll cost your husband a cool $1,000.

TOM: While the valves are unlikely to burn out while you're driving around town, it certainly can happen on, say, an 1,100-mile trip. So tell your hubby to add to that $1,000 the towing fee, the hotel and the dozens of roses it'll take to even begin to make it up to you.

RAY: An exhaust leak near the front of the car can let exhaust gases into the ventilation system. And that can kill you. Even if the leak isn't up front, if you're driving an old heap, like a '92 Civic, with rust holes in the floor because its cheapskate owner didn't take care of it, passengers could end up breathing fumes.

Dear Tom and Ray:

To do a quick check on an alternator, I was told that you could start the car and then remove the negative battery cable. Doing this would allow you to check whether the alternator is putting out enough current to run the vehicle. If the engine cuts off, it is a sure sign that the alternator has died. What are your thoughts? I can't find anything concrete.

-- Cory

RAY: You might need to be standing behind something concrete when you try this.

TOM: Actually, you can stand near the car, but you'll want to have your wallet out and at the ready. You'll certainly fry the voltage regulator, and possibly the alternator and other electronic components, too.

RAY: The car's battery is just there to power the starter and get the car started. It took the place of the crank (which my brother no doubt remembers).

TOM: Yeah. I was married to her for 15 years.

RAY: Once the car starts, the battery's job is done. Electricity to fire the spark plugs comes from the alternator, which is powered by the engine. And any additional current that the alternator makes is used to recharge the resting battery.

TOM: In the old days, your test would work. If the engine needed power from the battery too it would die.

RAY: But when carmakers switched from mechanical voltage regulators to electronic regulators, the test stopped working.

TOM: You take the battery cable off, you say, "Hey, it's still running . . ." PFOOOFFF! ". . . What was that?"

RAY: So if you're concerned about your alternator (if your battery or generator light is coming on), take your car to a shop and ask your mechanic to do an alternator output test. It'll cost you a few bucks, but it's a lot cheaper than a new voltage regulator.

Got a question about cars? Write to Click & Clack in care of The Post or e-mail them through the Car Talk section of the Cars.com Web site.

(c)2002 by Tom and Ray Magliozzi

and Doug Berman