THIS STORY HAS BEEN FORMATTED FOR EASY PRINTING
ASK THE EXPERT

The Car Doctor - January 31, 2008

Email|Print| Text size + By John Paul, AAA Car Doctor
January 31, 2008

Q. I was looking at a Mazda Speed 6 with a 4-cylinder turbocharged engine. It states that premium gasoline should be used. Could you go with the mid-grade or regular? How bad would that be for the engine and the turbo?

A. The Mazda Speed 6 uses a 270-horsepower engine, and to take full advantage of this performance, premium fuel is recommended. The computer in the car will compensate for lower octane fuel, but performance and fuel economy will suffer. The Mazda Speed 6 averages about 19 miles per gallon. If you drive an average of 12,000 miles per year, using premium fuel will cost you about $127 more per year than regular unleaded. In my opinion, the performance gain is worth the $10 per month for premium fuel.

Q. I've been reading on the web that narrower winter tires give more control than wider ones. I'd like to know if that is true, because the standard size for my Subaru Tribeca 2008 is 255/55/18, and I wish to go down to 235/65/17 if I could achieve better handling and saving at the same time.

A. A wide performance tire tends to plow through snow, which causes more resistance and in some cases poorer handling. A narrower tire gets through snow a bit easier and may improve slow speed traction. Downsizing may make some sense if you drive on unplowed roads or through deep snow on a regular basis. Still, switching to a smaller, narrower tire could degrade the handling during everyday (non-snowy) driving.

Q. My 2003 Nissan Maxima SE has 78,000 miles on it. I have maintained the car following all the recommendations in my car's owner's manual, but I am hearing a ping/rattle noise when I speed up from 20 to 40 mph. It comes on and off and goes away when the car reaches 60 mph. I always use premium fuel. What do you suggest?

A. Engine ping or detonation could be caused by a couple of problems. Your vehicle has an EGR valve, which is designed to re-circulate exhaust gas and lower combustion temperatures. If the valve is clogged, the combustion temperature will rise and cause engine ping. The other common problem is a buildup of carbon in the engine. Cleaning out the carbon is a relatively simple procedure that uses a chemical to dissolve the carbon in the engine.

Q. My 1997 Grand Am shuts off while I'm driving. I start it up and drive for about a mile, then it shuts off. It restarts, but then after a mile it shuts off again. What is wrong?

A. In the most basic sense, an engine needs fuel and an ignition to run. In the case of your car, you are losing one or the other. The most common problem with models similar to yours is a faulty crank shaft sensor, which would cause a loss of ignition.

Q. I have always wanted a sporty sedan, and I have looked at the BMW 535 and the Audi A6. The interiors look great and they handle well, but I have never bought an import car before. Do you have any other suggestions for a sporty sedan?

A. I recently spent a week in the Cadillac CTS with the new 304-horsepower direct injection engine and would consider this equal to - if not better than - the cars you have looked at. The interior was equal to the Audi A6 and the ride, handling and performance was equal to, if not better than, the BMW. Although I have never been a Cadillac fan, this new CTS is competitive with any sports sedan on the market.

more stories like this

  • Email
  • Email
  • Print
  • Print
  • Single page
  • Single page
  • Reprints
  • Reprints
  • Share
  • Share
  • Comment
  • Comment
 
  • Share on DiggShare on Digg
  • Tag with Del.icio.us Save this article
  • powered by Del.icio.us
Your Name Your e-mail address (for return address purposes) E-mail address of recipients (separate multiple addresses with commas) Name and both e-mail fields are required.
Message (optional)
Disclaimer: Boston.com does not share this information or keep it permanently, as it is for the sole purpose of sending this one time e-mail.