Drive it forever : Alloy wheels require TLC

Dear Mike:

I live in an area where they use a lot of chemicals on the roads in winter. I have noticed the alloy wheels on both my jeep and my truck are getting pit marks on the rims, and there are more severe marks where there used to be wheel weights.

Any cure for either problem?

A: Virtually all alloy wheels are painted with silver paint and/or clear-coated. Wheel-balancing weights that clip on scratch that paint, letting corrosive moisture and road salt get to the underlying aluminum. Ditto for any scratch marks either made by a careless technician who pops off a tape-on weight with a casual flick of a screwdriver or from the occasional brush with road debris or curbs when parking.

Now that the pitting has gotten a good hold, you’ll need to have those wheels refinished. Any decent body shop can do this repair. Never sandblast alloy wheels, or any other aluminum alloy components. The coarse surface left behind is great for holding paint, but represents millions of tiny stress risers. Those stress marks will degrade the strength of the wheel. Acceptable methods include glass-beading or blasting with crushed walnut shells, polymer media or baking soda, as well as chemical paint remover. Any corrosion pits need to be sanded down, not just filled in with Bondo.

Severely corroded wheels can fail, so don’t neglect them. A generous layer of wax will help repel water and salt.

Dear Mike:

In a recent column, you made some good observations but neglected a major problem in regard to not letting a car warm up completely: the exhaust system.

I had an acquaintance that had to replace the entire exhaust system in his Chrysler once a year, and it was because he drove the car six blocks to work and shut it off only to do the same thing going home. The exhaust system simply must be allowed to warm enough to stop the destructive corrosion from engine combustion.

A: What you say is correct. But since catalytic converters have become ubiquitous, exhaust systems are made from far better steel to deal with the intense heat. Also, the catalytic converter itself adds a fair amount of heat to the system, drying out the system rapidly after start-up. So these days, exhaust systems last far longer than we were used to a generation ago.

Dear Mike:

What time of year is harder on a car battery, summer or winter? Any help you could give me on this matter would be great.

A: Winter makes the most demands of a car battery.

The cold, stiff oil requires the battery to provide the maximum amount of current to turn over the engine at a time when the cold battery can provide the least energy. The winter-heavy electrical load on the rest of the car means the battery will have less than a full charge available much of the time.

On the other hand, high under-hood temperatures during summer can damage a battery by increasing water loss in the electrolyte. So winter is when most batteries fail, but it’s from damage done during hot weather.

Dear Mike:

I recently purchased a 2002 Chevrolet Tahoe, but we’ve had a very frustrating annoyance since we bought it: Cold air blows inside the car from somewhere under the dashboard on the passenger side, as well as through the heater vents when the heater is on.

Any help to find the cause of this problem would be helpful because none of the shops where we live have ever heard of it.

A: It could be something as simple as a vent hose that has come adrift under the dash. Or a misaligned heater plenum, or a blend air door that’s not closing all the way or a missing foam rubber seal, or a vacuum hose that controls something that’s split open or … a lot of things. Someone will just have to get under the dash and look — preferably someone who has a clue as to what to look for.

A lot of mechanics don’t like to do under-dash work. It’s hard working upside down in the close confines of the foot-well. Go to someplace that specializes in A/C work.