clock menu more-arrow no yes

Filed under:


Dear Tom and Ray - I have a 1994 Buick LeSabre with 19,000 miles. The car runs perfectly, except after it is parked in our carport. Occasionally, in the morning, I find a water puddle under the exhaust pipe about 6 inches in diameter. There seems to be a black carbon substance on top. It is not greasy and does not seem to be oil. This occurs about once a week or so at irregular intervals. We use the car for city driving, although we do some highway driving as well. What is this stuff? - Sidney

RAY: It's good old H2O, Sidney. Water is one of the byproducts of combustion, so it's produced whenever you run the engine.

TOM: And when you use the car for short trips, the exhaust system never really gets hot enough to evaporate the water, so some of it condenses and drips out the end of the tailpipe.

RAY: And since carbon (or "soot") is also a byproduct of (incomplete) combustion, all exhaust systems have some carbon in them. So the water takes a little bit of carbon with it, and that's what you see on the surface of the puddle.

TOM: It's perfectly normal, Sidney, and nothing to worry about. You might even take advantage of it by parking the car with the tailpipe hanging over your perennial bed. That'll save you from watering it a couple of times a week - assuming you don't mind a little soot on the petals.

Dear Tom and Ray - I am hoping you can help with a problem I am having with my wife's 1967 Camaro convertible. She drove it daily to work until about a year ago, when this problem developed. Four different mechanics can't find the problem. It burns up a set of spark plugs in less than a week. All of the burned plugs are black with soot and they all look the same.

The motor, which was completely rebuilt six years ago, is a 327 V-8. Two people have rebuilt the carburetor, and then we bought two rebuilt carburetors. I also had the valve seals changed, even though the car doesn't use oil.

Two of the mechanics tried hotter plugs. I had a new coil and distributor put on. The compression is good. Any advice or direction would be greatly appreciated. - Richard

TOM: I'll bet you want some advice or direction, Richard. Especially now that you've spent a thousand bucks and 23 weekends trying to fix this thing.

RAY: I think you have an obscure problem called "manifold burn-through."

TOM: I had that once after eating at my mother's house. I was chewing antacids for about a month after that.

RAY: In this particular engine, some of the hot exhaust is sent through a passage in the intake manifold. Why do they send hot exhaust through the manifold? Because it runs directly underneath the carburetor, and heats it up, which makes the car warm up faster and run more efficiently.

TOM: But when the engine gets old enough, that hot exhaust can burn a hole right through the manifold. All it takes is a pin hole. And then that hot exhaust gets sucked into the carburetor where it contaminates the fresh mixture.

RAY: And if exhaust is getting sucked into the carburetor instead of fresh air, the engine will suffer from oxygen starvation and will behave as if the mixture is way too rich (too much gas, not enough air). And what's the sign of a too-rich mixture? Black spark plugs! So remove the intake manifold and check for a pin hole under the carburetor. I think you'll find one.

TOM: Brilliant! Brilliant, Raymond. What a brilliant deduction!

RAY: Well, it'll be brilliant if it's right. If not, what's another eight or 10 weekends in the driveway, right, Richard?

If you want to ruin your car, we have 10 ways for you to do it. If you don't want to ruin your car, we have "Ten Ways You May Be Ruining Your Car Without Even Knowing It!" You can order this booklet by sending $3 and a stamped (55 cents), self-addressed, No.10 envelope to Ruin No.1, PO Box 6420, Riverton, NJ 08077-6420.