"When your engine is up and running," says Robert J. Sinclair Jr., at the New York chapter of AAA, "you can learn a lot by what comes out of the tailpipe."

Blue: You're burning oil, which means your valve guides and piston rings are bad.

White: You're burning coolant (antifreeze). The head gasket is probably the trouble.

Black: You're burning excessive fuel. In a new car, it usually means bad fuel injection. In an old car, you may need a carburetor adjustment.