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The Car Doctor

Inaccurate speedometer, tune-ups, overheating in traffic

By John Paul, AAA Car Doctor
July 17, 2008

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Q. I have a 1999 Kia Sportage and my speedometer told me I was going 45 miles per hour. The problem is that I got pulled over and was told I was going 60 miles per hour. Can you tell me what's wrong, and how much it would cost to fix it?

A. Your car's speed monitoring system consists of the speedometer mounted in the dash, and a speed sensor mounted on the transmission. The problem could be with the speed sensor or the speedometer head itself. If you recently changed the tires on your vehicle to a much larger size this will cause the speedometer to read a lower than actual speed.

Q. I have a 2005 Nissan Altima 3.5 SE with 63,000 miles on it. How often do I need a tune-up for the car? I have heard from some mechanics that it isn't necessary to get a tune-up until the car reaches 65,000 to 70,000 miles, due to the fact that the spark plugs are platinum-tipped, and other parts are more durable than in the past. What is the correct answer?

A. The term "tune-up" almost doesn't apply to today's cars. The spark plugs in your vehicle should be good for up to 105,000 miles, although this doesn't mean maintenance can be ignored. The fuel and cabin filter need to be changed on a regular basis. Drive belts, hoses and fluids all need to be checked and maintained. When in doubt, consult your car's owners manual for recommended maintenance schedules.

Q. I own a 2006 Infiniti G35 coupe, and of course, Infiniti recommends premium grade gasoline only. What is your opinion on that? Do I need to use premium grade every time I fill up?

A. Computer systems on cars manufactured since 1996 prevent engine damage when you choose to use lower than recommended octane gasoline. Although to get the best performance as well as maximum fuel economy you should use the grade of gasoline recommend by the vehicle manufacturer.

Q. I have a 2005 basic model Acura TL that needs some fixing, but I am having trouble locating some parts: the windshield fluid reservoir tank, lower bumper grills, front passenger side suspension components, and some other parts. However, when ordering other parts, I noticed that some parts are interchangeable with the Honda Accord. Do you know which parts are interchangeable, or where I can find a list of interchangeable parts? Any help would be greatly appreciated.

A. A good salvage yard should be able to cross-reference the Honda parts to the Acura parts. Many salvage yards, such as All Foreign Auto Salvage in East Bridgewater, use the Hollander interchange to cross reference one part to another.

Q. I have a 1999 Chrysler Town and Country that overheats when I am in a drive-thru, in stop-and-go traffic and when I am idle for a while. I usually turn the heat all the way on, with the dial to the floor as the manual instructs me to. This helps with the overheating, but only temporarily. I need some advice: I can't drive for an hour without this problem occurring. If I'm able to keep moving consistently, there's no problem.

A. The problem is more than likely with the electric cooling fans. At highway speeds there is enough airflow across the radiator to keep the engine at operating temperature. But at lower speeds, the cooling fans need to pull air through the radiator to prevent overheating. The problem could be a faulty fan, coolant sensor or fan relay.