Dimples
I was detailing my '02 GMC Sonoma after having it stored in my parents' garage while I was in Iraq. The truck has a manual transmission and neither of my parents can drive a stick shift. So, they started up the truck and ran it occasionally, but they didn't drive it. When I had the truck out in the driveway cleaning the wheels and tires, I noticed what appears to be a dent or dimple in the sidewall of all the tires. The air pressure was at most 2 psi below what it was when I left, so the tires didn't go flat. I drove the truck, and the tires seemed a little "lumpy" at first, but that feeling went away after a few miles. The tires are relatively new with probably 80 percent tread left. Did storing my truck and not moving it damage the tires? Did this cause a weak spot that might blow out? Do I need to get all new tires or is this not anything to worry about?
Mike Sullivan
St. Joseph, Missouri

If the flaws go in but not out, the problem is only cosmetic. These low spots or dimples are common. They tend to show up best on a sunny day after you've washed your truck and applied tire protectant. The dimple is a minor void in the splice of the rubber. The dimples aren't mold marks or signs of overlapping steel belts. If you look carefully at a lot of tires, you'll find these dimples on all types and brands of tires. Some tires have more than one low spot. The kind of flaw you need to be aware of is anything that protrudes. A blister or bubble can indicate a weak spot that could lead to a blowout.

It Doesn't Make Sense
My '95 Ford F-150 (the engine is the 351 V-8) failed its annual emissions test. A friend suggested that the oxygen sensor could be the problem. He said I could simply remove the old sensor, clean it, and reinstall it. That sounds better than buying a new sensor, but I've never heard of cleaning an oxygen sensor. Is it similar to cleaning spark plugs?
Bill McIlhinney
via e-mail

Your friend appears to be one of those people who have just enough knowledge to be dangerous. A bad oxygen sensor is a common source of emissions test failure. It's possible to remove and clean the sensor, but it's more futile than fruitful. The cleaning may work temporarily, but you can be sure it won't work for long. A new oxygen sensor for your truck should cost around 50 dollars. You'd be better off to have your truck diagnosed at a tune-up shop. If they tell you that a new oxygen sensor is needed, you can make the swap yourself. Just remember to let the exhaust cool before you touch anything.