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Car Doctor: Flushing automatic transmission fluid may be temporary fix

Posted by John Paul  April 8, 2011 09:47 PM

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Q. I have a 2000 Mitsubishi Montero with a six-cylinder engine and automatic transmission. A few months ago the vehicle would start to buck when going up a hill. From previous experience, this usually indicated the spark plugs needed to be replaced. My mechanic replaced the plugs, but the bucking continued. His next solution was to flush the transmission and replace the fluid.  After changing the transmission fluid the problem seems to be resolved. Could you explain how dirty transmission fluid would cause this type of problem? 

A. Nearly every automatic transmission has a lock-up torque converter (fluid coupling). The torque converter will lock up at speeds of about 15-40 miles per hour. As the torque converter begins to fail, or the transmission fluid breaks down, the fluid will tend to overheat. Replacing the fluid replenishes the various friction modifiers and restores normal transmission operation.  Depending on the condition of the transmission, this may only be a temporary repair.

Q. We have a 2007 Jeep Grand Cherokee. When the heater fan is off and the dial placed in the blue zone, heat still comes through the vents. The only way to stop heat is by turning on the air conditioning. Any ideas as to the problem and how much can I expect to have it corrected at the local Jeep dealer?

A. The problem is most likely with the heater blend door or blend motor. Like its name implies the blend door mixes hot and cold air to keep the cabin temperature comfortable. The repair can be quite costly since the dash needs to be disassembled. That said, some technicians have found shortcuts by cutting away part of the ductwork to access the blend door. With this type of job I would shop around at dealers, independent shops, and radiator specialists.

Q. My mother has a 2000 Toyota Camry which has had probably a dozen emissions problems starting at 22,000 miles and over time has cost a fortune.  Now the motorized component letting her move her seat has broken and it will cost almost $2,000 to fix.  Is she getting scammed or does she have other options? 

A. The price does in fact seem high; the motor that runs the power seat is about $500. I can’t imagine why the dealer is suggesting that it will take nearly 15 hours to replace the faulty part. Now if the seat is stuck in a comfortable position and your mother is the only driver, it may not be necessary to fix it.

Q. I have seen the commercial for the Kia Optima. The car looks very stylish, almost a little Jaguar like. Have you driven this car and what do you think?

A. I will certainly agree that the silhouette of the car is stunning, although I’m still warming up to the grill. The ride, like many Kia products, is a little stiff. The fuel economy from the 2.0-liter direct-injection turbocharged engine is 22 mpg in the city and 34 mpg on the highway. With 274 horsepower on tap, most drivers should be more than satisfied with the car’s overall performance. The interior materials are contemporary and rich looking and all the controls are straightforward and simple to use. Overall I would say the Optima is a homerun for Kia. 

Q. My car recently started to make noise when making hard turns.  My local mechanic checked the power steering but did not find anything.  Now, after the car warms up I get a noise that sounds like squeaky springs and the rubbing noise when I turn.  What should I do?

A. The noise could be from a faulty power steering pump or simply a loose or worn power steering belt. At this point I would find a repair shop that will go on a road test with you, so you can demonstrate the problem. Once they have identified the problem, get an estimate and ask them about their warranty.

John Paul is the public affairs manager for AAA Southern New England. He can be reached at or on Twitter @johnfpaul.

This blog is not written or edited by or the Boston Globe.
The author is solely responsible for the content.

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Clifford Atiyeh is an automotive writer and car enthusiast . He has spent his entire life driving cars he doesn't own.
In the garage: 1995 21-speed Iron Horse, 2002 Jeep Wrangler X (by association)
Bill Griffith is a veteran Boston Globe reporter, having reviewed cars for more than 10 years and serving as assistant sports editor for 25 years. He was also the paper's sports media columnist.
In the garage: 2006 Subaru Baja
AAA's Car Doctor, John Paul John Paul is public affairs manager for AAA Southern New England, a certified mechanic, and a Globe columnist. He hosts a weekly radio show on WROL.
In the garage: Hyundai Sante Fe, Chrysler PT Cruiser convertible
Craig Fitzgerald has been writing about cars, motorcycles, and the automotive industry since 1999. He is the former editor of Hemmings Sports & Exotic Car.
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Keith Griffin is president of the New England Motor Press Association and edits the used car section on He also writes for the Hartford Business Journal and various weekly newspapers in Connecticut.
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George Kennedy is a senior writer for WheelsTV in Acton, which produces video reviews for Yahoo, MSN, and other auto websites.
In the garage: Lifted 1999 Jeep Cherokee
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