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THE CAR DOCTOR

Would you buy this Pontiac G6?

Plus: Vandalized with sugar, Volvo oxygen sensors

By John Paul
Boston.com Columnist / February 23, 2009

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Q. Would you purchase this car? It is a 2005 Pontiac G6 base sedan with 40,000 miles. The price is $9,800 and there is no warranty. The Carfax report shows oil intervals between 10,000 to 15,000 miles. The car was from a General Motors auction and has had the steering column replaced. What do you think?

A. On the surface the price seems reasonable but with oil changes outside the manufacturer's recommendation and no warranty, the car makes me a bit leery. Although it is certainly possible there were other oil changes not reported. Add to this a steering column replacement which could indicate a possible theft, I might be tempted to keep looking.

Q. My 1992 Geo Storm ran fine for three months. Not long ago, at a stop light, the car stalled. I had it towed home and on two different occasions the car started but ran for only 30 seconds or so then died. The car has spark at the spark plugs but when I looked at a sample of fuel there were tiny sparkly particles. What is going on?

A. The sparkling particles may be sugar in the gas. If it is sugar, it may have clogged the fuel injectors. You could remove a fuel injector and look at the spray pattern. The spray pattern should appear in a cone shape, if not, the injector is clogged. If the car was vandalized by putting sugar in the fuel tank, you will need to remove the fuel tank, wash out any contaminated fuel, replace the fuel filter, and possibly replace the fuel injectors.

Q. I'm considering purchasing a 2004 Lincoln Aviator. The owner's manual recommends using premium gasoline only. What threats exists by regularly using regular unleaded gasoline in a vehicle like this?

A. The electronics in the vehicle will adjust for the lower octane fuel so you don't need to worry about engine damage, however, before using 87 octanes, you might want to perform a simple test. Calculate the fuel economy using premium fuel and then compare the results using regular fuel. In my experience, the premium fuel returns better fuel economy and is actually cheaper to operate the vehicle in the long run.

Q. I have a 2001 Volvo V70 2.4T. Recently the "check engine" light has come on a few times. I brought the car to a major auto parts store where I was told the problem was with an O2 sensor. I called Volvo and they said their reading may be different and I should have the code read at a Volvo dealer. I have heard that for Volvo to do this job they would need to replace both of the O2 sensors, and they are expensive. Can I just replace the oxygen sensor?

A. It is a nice service that some auto parts stores will read computer trouble codes at no charge, but sometimes you get what you pay for. An oxygen sensor code may not mean the car actually needs an oxygen sensor. The dealer or a competent repair shop will read the code, but will also analyze the additional information as it relates to the fuel system before replacing any parts. The problem could be one or more faulty oxygen sensors, but it also could be a vacuum leak.

Q. We own two Chevy Luminas; one is a 1996 and the other is a 1998. On the 1998, we replaced the head gasket at 75,000 miles. The car now has a mileage of 145,000 and the same problem is happening again. Our mechanic added some sealant, but I was wondering how much longer we can count on driving it before the head gasket goes completely.

A. There is no way to determine how long the sealer will hold. Since you know the problem exists, the best thing to do is check the coolant every couple of days. It is possible that you may get many more miles out of the car as long as you don't allow the coolant to run low and the car to overheat.

John Paul is the public affairs manager for AAA Southern New England. He can be reached at jpaul@aaasne.com.