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 car port. Occasionally, in the morning, I find a water puddle under the exhaust pipe about six 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 by-products 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 by-product 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 tulip 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.