Was Dad Right? Re-evaluating Warm-ups with the Exhaust System
Q: In a recent auto clinic Q&A, you made some good observations but neglected a major problem of 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 cat itself adds a fair amount of heat to the system, drying out the system rapidly after startup. So, the exhaust system will last far longer than we were used to a generation ago. The most common exhaust failure nowadays is rubber hangers, and accordion joints.
Time of the Season: Winter's Ware on Batteries
Q: 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 underhood temperatures during summer can damage a battery by increasing water loss in the electrolyte and speeding up sulphation.
So, winter is when most batteries fail, but it's from damage done during hot weather.
Mating Problems: Indexing Rims Accurately on the Hub
Q: I'm hoping you can answer this one for me since I can't get an answer from anyone: I have noticed on older Volvos and older Mercedes (1983 and up) that the alloy rim is "indexed" specifically to the hub/mating surface. The Volvo brake rotors often have a stud that holds the rotor to the hub, but also protrudes about 2 in.
Coincidentally, the inside mating surface of the alloy rims only have a hole deep enough on one location, basically forcing you to mount the rim to the hub on that small stud at a specific point. Why? Isn't the tire balanced to the rim enough? Why don't all cars have this feature?
A: Car manufacturers have found that there are better ways to position the rim accurately on the hub. Most cars use a centering hub nowadays. Now that virtually all tires are dynamically balanced, it's not as necessary to index the rim to one position on the hub.
Cold Air Blows In: Finding a Mechanic Who Works Underdash
Q: 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: Well, it could be something as simple as a vent hose that's come adrift underdash. Or a misaligned heater plenum, or a blend air door that's not closing all the wa,y 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 underdash work. It's hard working upside-down in the close confines of the footwell. Go to someplace that specializes in A/C work.
HAVE A CAR PROBLEM OF YOUR OWN? ASK MIKE AT PMAUTOCLINIC@HEARST.COM! (HE'LL ANSWER.)