Automania/Repair and Maintenance

AUTO QUESTIONS AND ANSWERS FOR WEEK 41

by Bob Hagin

Q. Our 1989 Mazda MPV van has about 90,000 miles on it and I've had to put several pairs of front tires on it during that time. The rear tires are OK but the inside edges of the fronts wear out in about 30,000 miles. I've had it the alignment gone over each time I've replace the tires but it is always within the specifications. I've rotated the tires religiously but nothing seems to work. Twice I has one shop replace the tires and do the alignment but the last time I had another shop do the job. The second shop hasn't had any more success than the first and I'm wondering if these vans all eat up front tires. K.B. Boise, ID

A. I understand that the Mazda MPV vans of that era had some troubles with the installation on the front crossmember and you'd do well to have that checked out at a dealership. I would guess that it's no longer a factory fix but you could ask. If the tire sizes are correct and the alignment specs are right, better have someone check to see if the chassis is diamond-shaped. Check the wheelbases (center of front wheel to center of rear on the same side) and they shouldn't vary by a quarter of an inch. Then check the chassis structure by measuring from any pickup-point on the left front to another point on the right rear. Then do the same check on the other side. Use the same but "mirror-twin" points. Again, the limit is about a quarter of an inch. This will tell you if the chassis is skewed and slightly diamond shape. This check is particularly important with a car, van or truck that has been involved in a collision. A skewed frame or unit construction can be pulled back into shape but it takes an experienced technician using good equipment.

Q. When I drive my 1991 Nissan Stanza at a particular speed, around 20 MPH, there's a rattling noise under the car. The noise reaches a high point and then goes away at around 25 MPH. It sounds like tin rattling but I looked under the hood and can't find anything that is loose or could be the cause of the problem. I don't have a mechanic that takes care of my car so I'm kind of on my own. The noise doesn't seem to be getting any worse and the car has around 60,000 miles on it. B.S. Monterey Park, CA

A. Sometimes the heat shielding on the exhaust system of those Nissans will rattle when the engine get up to a particular RPM range. It sounds a little like tapping very fast on a piece of sheet metal with end of a screw driver. When the engine gets to the end of that RPM range, the vibration is dampened out and the noise goes away. If you get under the car and tap on all the sheet metal shielding that's around the exhaust system with a rubber mallet, you can often locate the source of the noise. Since those kinds of vibrations often shake nuts and bolts loose, take a flashlight along and check the fasteners that hold those things together. But be careful. Even though they may be unscrewed, those exhaust system fasteners may be rusted solid. Spray them with penetrating oil (not a lubricant) to soften the rust or they break. A broken stud or bolt in an exhaust system can be a nightmare to fix.

Q. I'm considering buying a used Ferrari or some such collector's car as an investment that I can also drive just for the fun of it. I've followed the market for a while and wonder what the current thinking is on the collectible car market. I don't want to buy something and then have to bottom fall out of its value. D.W. Delray Beach, FL

A. The rarefied world of investment cars is so volatile and my experience is so limited that won't make a suggestion. A lot of people have made a lot of money in the business by manipulating the worth of exotic cars at the expense of beginners who don't understand the game. My opinion is that a neophyte has a better chance of winning in a street-corner shell game than investing in a big-ticket car.