Car Questions, Answered

Car-Maintenance Tips

Road block: Your dashboard light says check engine, but how soon do you need to do so?

Best route: "If the light is flashing, which happens in most post-1996 models, driving even another block could cause expensive damage to the catalytic converter (which reduces emissions), so you need to pull over immediately and call a tow shop," says Liz Dally, a master automobile technician and the owner of the Hawthorne Auto Clinic, in Portland, Oregon.

If the light is on but not flashing, there's a chance the problem is something you can fix yourself, like a loose gas cap. Pull over as soon as it's safe and turn the cap clockwise until you hear three or four clicks. If the warning light is still on, check the manual to see if there are any other easy fixes to try, such as making sure the oil dipstick is in all the way (check the manual for the dipstick's location under the hood).

Filling the gas tank while the car is running―a bad idea―can also cause the check engine light to come on (it will shut itself off eventually). If none of this works, call for an appointment to have the engine looked over. Any professional repair shop should be able to do the job; just ask if it has a scan tool for the make of your car. The shop will need that to find out what caused the light to come on.

Road block: You’re confused by the different gases at the pump. Which should you use?

Best route: Premium gas isn't cleaner, purer, or better than regular. The difference has to do with how it combusts. "Every vehicle is engineered for gasoline with a specific octane rating," says Chris Thomas, the chief engineer of vehicle research for Honda Research & Development Americas. The recommended rating might be printed on the interior of your gas-cap door, or you can look in your owner's manual. Most vehicles take regular unleaded gas (87 octane), but heavy trucks and high-performance cars often require higher-octane fuel (typically 91) because their engines have been tuned for extra horsepower. You'll get no benefit from using a higher-octane product than the manufacturer intended. But if your manual calls for a premium grade, using something with a lower octane rating will reduce performance and fuel economy, and can prematurely age the engine.

Road block: You need a good mechanic.

Best route: To find a reliable shop, ask friends for recommendations. Or look at the Mechanics Files at cartalk.com, an online bulletin board that dishes about particular mechanics. Check that anyone you're considering has been certified by the National Institute for Automotive Service Excellence (ASE), or that the shop is an AAA-approved repair facility. Ask questions or look for the certificates on the shop wall. The ASE also awards Blue Seal honors to outstanding repair shops. For a list of those near you, go to aseblueseal.org.