Q: I have a 2016 Chevy Tahoe for which the recommended tire pressure is 35 psi. When I start out, it reads 35, but after 20 to 30 minutes of high-speed driving, the tires are up to 38. Should I reduce pressure to 32 so it will be 35 at speed?
A: No. Absolutely not. Never. When driven, tires flex, and that causes friction, which creates heat, which, in turn, increases the air pressure. Engineers factor this in when establishing the tire pressure. The tire pressure sticker on your driver's door says "cold," meaning the pressure before driving.
Playing it safe
Q: Reading your recent column about tire tread depth, I have one observation to add. With most of the tires I have owned, once they get below half wear, they have significant loss of traction especially in wet weather. I had Continental tires that had markings for snow traction, wet traction and dry traction. As the tread got lower, wet traction took a nose-dive. As soon as my tires start having significant loss of grip, I replace them. My life is worth more than an extra 5,000 miles.
A: Agreed. The penny test with the 2/32 (1⁄16)-inch depth is the minimum at which tires should be replaced. It doesn't mean that you have to wait that long.
Oil not the culprit
Q: I have been using synthetic oil for the past three years in my 2004 Grand Cherokee with a 4.7-liter engine. Two months ago, when stopped at a stop sign, the oil gauge dropped to 0 (the engine sounded fine, however). I put it in neutral and revved up the engine, and the pressure returned to normal.
The mechanic I have been using for years had no idea except to try using regular oil again. But the problem returned. The mechanic had flushed out the engine before putting in the different oil. The water pump also failed one week after all this was done, but I'm not sure if the two situations are connected. Got any ideas?
