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Speedometer error, will it affect the re-sale value?

Posted by John Paul  August 24, 2011 04:23 PM

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Q. I own a 2010 Mini Cooper S convertible. It is equipped with a digital speedometer along with a very large analog speed display. I noticed through using my GPS that the speedometer reads 3 MPH greater that the actual speed of the vehicle. I contacted my Mini dealer about this problem. He told me that the speedometer error is within BMW specification. He said the error is due to different wheel size options for this model. I think that this error must affect my onboard computers, mpg readings, trip computers, service notices etc.? Won't my odometer read much higher miles over time effecting resale value?

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A. The GPS is generally more accurate than the speedometer; this is the case in most cars. Although a tire size change can affect the speedometer, the cars speedometer is calibrated to allow the factory to change tire sizes. What you are seeing is typical, most vehicle manufacturers allow a couple of miles per hour plus or minus over the displayed speed. Based on your estimate, at 120,000 miles your car’s speedometer will read 126,000 miles. I don’t believe this would be enough of an error to affect the resale or trade in value.

Q. I am the original owner of a 2005 Honda Accord with about 60,000 miles. After stopping for lunch during a recent trip, the car took longer than usual to start, about twice as long. Since then, the problem has happened many times but not always. It seems that the first start in the morning has no problem but starting later in the day are likely to take longer (but not always). My independent mechanic didn’t have an answer. I then went to the Honda dealer, where they tested the battery and suggested that the spark plugs could be a problem. So my question here is this: how likely is it that the longer starting time is due to needing new plugs or is there another likely cause for my problem?

A. The spark plugs in your Honda are generally good for 100,000 miles. So unless there is some sort of miss-firing I wouldn’t suspect the spark plugs. Diagnosing a problem that is intermittent is one of the most difficult tasks for a technician to perform. A couple of items come to mind, the fuel pump or relay could be starting to fail cause low fuel pressure when the engine is hot. The other possibility is there could be a slight flooding situation. This could be due to problems with the evaporative emission system or a leaking fuel pressure regulator.

Q. I recently read that the President is backing a plan to have the average fuel economy for cars sold in the United States to be over 50 miles per gallon. Do you think this is possible?

A. The 54.5 mile per gallon mandate is proposed to happen over time by 2025. As electric vehicle technology improves, increased use of hydrogen and other alternative fuels it certainly seems possible. In addition there seems to be some fuzzy math involved to get to this 54.5 miles per gallon number. It will be interesting to see how this plays out, this mandate may also require the use of smaller, lighter fuel efficient vehicles, something that typical American buyer have shunned.

Q. I have read your favorable comments about the Fiat 500, I like it but I’m concerned about how small it is. Do you think it would be okay for a highway commute? I drive about 70 miles on the highway each day.

A. I recently drove a Fiat 500 to Maine and found it more than up to the task. This new Fiat, unlike smaller cars of the past is designed to be an everyday car that can handle year round driving challenges and be fun to drive. The one issue with the Fiat 500 is how much attention it attracts, people smile and wave whenever they see it.

Q. The brake pedal on my car will sometimes slowly drop to the floor. When I jump on the brakes for a panic stop the car stop great. I have checked for leaks but everything looks great. Is this a problem with the anti-lock brakes or is something else wrong?

A. You are describing a classic symptom of a faulty brake master-cylinder. The master-cylinder has a valve with rubber cups that over time the cups shrink. Replacing the master cylinder will get the car back in safe operating condition.

Q. I have a 2008 Town & Country with 20,000 miles, since new there has been a clanging noise from the exhaust when I shut the ignition off. The dealer said it’s normal and did try to adjust something but the noise is only getting worse. Can you help me?

A. This is noise is generally a result of the exhaust system cooling off and the heat shield or muffler baffles contracting. The dealer needs to isolate the sound to find a permanent fix.

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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.
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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.
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