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posted: 7/21/2013 12:10 AM

Cooling fan problem causes overheating

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Q. Why is it that my car tends to overheat when I am stopped at a light but will begin to cool down as I am going down the road? I also don't seem to have the problem when the air conditioning is on.

A. My guess, with the information I have, is you have a bad electric cooling fan.

On many cars there are two fans; one runs when the car needs to be cooled down and they both run when the A/C is on. The reason the car cools down when you are running down the road is you are getting some natural airflow across the radiator, which is doing the cooling.

It is possible there are other problems but this would be the most likely.

Readers write

A while back we had a reader, Bud, write in about his battery going dead on his 2006 Mustang when he let the car sit for a few days. Another reader named Rob then wrote that he had the same problem with his Mustang but, through some research of his own, he traced the issue back to a defect in the entertainment system. Rob found that if he made sure to turn the radio off and leave it in the AM/FM position, rather than switch the car off while the CD player was on, the battery would not go dead. Thanks for the great info Rob -- I recently got this note from Bud!

"Doug, I want to thank you for getting me the information on my battery problem. I let the Mustang sit for nine days with radio off in the AM/FM position and it started right up. The radio is the Shaker 500."

This reader responded to the problem John was having with his 2005 Nissan Pathfinder.

"Here is another possibility for the shudder vibration on the Pathfinder. I ran into a lot of lockup torque converters causing Mercedes cars to shudder when locking up, caused by coolant getting into the transmission fluid in the radiator to transmission cooler. This could be verified by shutting off the lockup with a shop computer and road testing." -- B. Wagner.

Thanks for the information Mr. Wagner. I agree if coolant is getting into the transmission fluid, that could cause many problems, including lockup torque converter issues. It would be good to establish if coolant is, in fact, getting in the transmission fluid. Because, if this is the case, it sounds like there may be some extended warranty coverage. If it's not, he may have something altogether different going on.

• Douglas Automotive is at 312 S. Hager Ave., Barrington, (847) 381-0454, and 123 Virginia Road, Crystal Lake, (815) 356-0440. For information, visit Send questions to

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