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AUTO Q AND A: Heat warning may be caused by trapped air

Q: I have a 1990 Mazda Miata that constantly seems to overheat. When I'm on the freeway, the temp will begin to rise; then I pull over, and it goes back down to just below the halfway mark. Most of the time, I can just start driving again, and th...

Q: I have a 1990 Mazda Miata that constantly seems to overheat. When I'm on the freeway, the temp will begin to rise; then I pull over, and it goes back down to just below the halfway mark. Most of the time, I can just start driving again, and the temperature doesn't rise again. I changed the radiator cap and the thermostat, but that hasn't solved the problem.

A: What happens if, as the temp begins to rise, you keep driving -- with an eye on the temp gauge, of course? Will it continue to climb into the red zone, indicating overheating? Or will it stabilize or fall back to normal on its own? If the latter, it may just be the thermostat finally reaching full open and allowing coolant to reach a stable temperature. If it continues to climb toward or into the red, the issue likely is air trapped in the cooling system, stalling the flow of coolant and leading to potential overheating.

Two things may be contributing to this. A buildup of corrosion and debris in the radiator may be reducing radiator capacity, leading to higher temperatures. Or air may be getting into the system. A system pressure test might identify an air leak, and a chemical flush or professional off-car radiator cleaning might keep operating temperatures under control.

Q: I have three Chevrolets: a 1998 Suburban, 1999 Malibu and 2002 Astro, all with stock AM/FM/CD in-dash radios. All of the radios have lamps that have burned out in the station select or AM/FM band select buttons. How do you replace the lamps? I have been concerned about pulling the radios out of the dash because if I open them up, I might trigger something in the anti-theft feature that I would have to bring in to a dealership to reset. I am a trained electronics technician, and this doesn't seem as if it would be that big of a deal. Any advice?

A: I did a little online research and find that most questions about fixing this problem are answered with "replace the radio." But I did find one forum where a fellow pulled the radio, opened it up and found a number of small, 12-volt bulbs burned out. He went to Radio Shack, bought similar little bulbs and soldered them in place. Since you're an experienced electronics guy, this may be the answer for you. As long as you know the security code, I don't think there are any security issues. Even if the radio displays "LOC" when you reinstall it and you don't know the code, you can extract a backup code, contact Delco and get the correct code.


After I advised scanning for fault codes on a BMW where the windows and moon roof appeared to open on their own, I received this wonderful "KISS" -- keep it simple, stupid -- reminder from John Borden:

"A recent issue of BMW's Roundel magazine addressed the same issue with a different conclusion: the key itself! Either the car has some fault whereby your suggestion of a coded diagnosis might prove useful, or the owner accidentally leaned on the fob, somehow triggering one of the exposed buttons. When held down in a certain position for a prolonged period, the system automatically opens all windows full open plus the moon roof. I bet this is what happened to the 5-series owner as well."

(Paul Brand's column has appeared in the Star Tribune for more than two decades. The author of "How to Repair Your Car," Brand is an automotive troubleshooter, driving instructor and former racecar driver. Send questions to Paul Brand, Star Tribune, 425 Portland Avenue South, Minneapolis, Minn. 55488 or paulbrand@startribune.com . Please explain the problem in detail and include a daytime phone number. It isn't always possible to send a personal reply.)

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