THE GOODS : Pay Heed If Your Car Is Sending a Smoke Signal

Question: I get heavy white smoke coming out of the exhaust pipe of my 1989 Mazda 626. Various mechanics have said my carburetor, crankcase ventilation valve or other things are to blame. It doesn’t seem to be affecting the car. Do you have an answer?

--M.F.

Answer: Engines smoke because something is wrong. So even though you don’t recognize it yet in the performance of the car, the smoke signals that a serious problem could be starting. White smoke typically occurs when either water or oil is entering the combustion chamber, which has rings, gaskets and seals to keep oil and water out of the cylinders.

The more serious problem would be oil getting in, most likely through worn piston rings, leaking valve guide seals or a bad head gasket. The valve guide seals are the cheapest to fix, followed by the head gasket. Worn rings mean the engine needs to be torn apart and remanufactured.

When oil is burned, it fouls the spark plugs with a tar-like substance. Your mechanic can easily check for fouled plugs. You might also keep track of your engine’s oil consumption, although it takes only a small quantity to produce a lot of smoke.

Water is less serious. Water usually enters the combustion chamber through a blown head gasket. When the water hits the hot gases, it forms clouds of steam. It is more obvious in cold weather and almost always dissipates quickly.

You should also carefully monitor your coolant level. If your radiator is mysteriously losing antifreeze and water, it may be going into your engine via a leaky gasket.

*

Q: I recently had the brake shoes replaced and the drums turned on my VW Beetle. When I picked the car up from the repair shop, it required a lot more force on the brakes to stop the car. The mechanic said this was because the shoes had to shape themselves to the drum. This is nerve-racking. Is that right?

--D.B.

A: The shoes should have been contoured to correctly fit the drum by the mechanic. A drum is circular and the shoes must have the same arc. If the shoes are too big, they will touch the drum at each end and if they are too small they will touch in only one spot in the center.

The right shoes should fit correctly without any adjustment, but in some cases the arc may not properly match up and the mechanic must make modest changes in the shoe.

Part of the problem may be that your mechanic is more familiar with modern disc brake pads, which are flat and always match the contour of the disc. But ignorance is no excuse for an unsafe brake job.