CAR TALK\Tire manager blowing a lot of hot air.

Byline: Tom and Ray Magliozzi 

Dear Tom and Ray: While getting a leaky valve stem fixed, my local tire store manager told me that I should be inflating my tires to the pressure listed on the tire, not the pressure listed on the door or owner's manual. In the case of my Taurus, he inflated them to 41 psi. This seems excessive. What is the answer - the pressure on the tire or the pressure recommended by the manufacturer?

- Jon

Ray: The tire store manager told you that? The manager? Holy crowbar! There's a guy with his headlight firmly implanted in his taillight socket!

Tom: The pressure printed on the sidewall of the tire is the maximum tire pressure. It's printed there as a warning, meaning "if you put more than this amount of air in this tire, it could blow up." It doesn't mean you're supposed to put that much air in there. What a knucklehead!

Ray: It's like the maximum speed of your car. Your owner's manual may tell you that your car has an absolute top speed of 120 miles per hour. That doesn't mean the manufacturer is recommending that you actually drive it 120 miles per hour.

Tom: The pressure printed in the owner's manual, on the driver's door pillar, or the glove box door is the recommended tire pressure. That's the pressure at which the car handles, rides, steers and brakes best. And unless you've changed tire sizes, that's the pressure you should always use. And for most cars, that pressure is between 28 and 35 psi.

Ray: Under no circumstances should you inflate your tires to maximum pressure. Not only will you risk a blowout, but you'll diminish your ability to control the car because your handling and braking will be much, much worse.

Tom: Not to mention the ride! How many scabs do you have on your head from bouncing up and hitting the ceiling since this guy overfilled your tires, Jon?

Dear Tom and Ray:I have a 1985 Mustang GT with a 5-liter engine. If I drive for a short distance (2 miles) and turn off the motor, when I start it up again the oil light comes on and there is no oil showing on the dipstick. The first time it happened, I added 3 quarts of oil, and when I got home later, the oil was way over the full mark on the dipstick. If I let the car sit for 30 minutes or more, the oil seems to reappear. The service department is stumped as to where this oil is hiding. What could be going on?

- Ric

Ray: That oil is orbiting the earth with the Van Allen radiation belts.

Tom: Just kidding, Ric. The oil is hiding under the valve covers. When the engine runs, oil gets pumped up into the valve train, which is at the top of the engine. Then it's supposed to drain back down into the oil pan, where it gets recirculated. But if the drain holes are plugged up, the oil just stays up there.

Ray: It happens to older engines, especially older engines whose oil hasn't been changed regularly. Gunk and crud build up on the inside of the cylinder head, and every so often, a piece of that crud breaks free, flows "downstream" with the return oil and gets stuck in one of the drain holes. It's kind of like when the gutters on your house get plugged up with leaves and the water pours out over the sides because it can't get through the downspouts.

Tom: Eventually, the oil seeps back down to the oil pan, which is why it reappears after half an hour.

Ray: You need to remove the valve covers and clear out those drain holes so the oil flows down freely, Ric. This is an operation that your mechanic will do with a precision tool - like a coat hanger.

Tom: And when you install your next engine in this car, change the oil and filter every 5,000 miles, OK?