Q. My 2001 Ford Crown Victoria emits an annoying intermittent squeaking sound from the rear right wheel area. It makes the sound no matter if it's wet or dry out. I've taken it to a Ford dealership, where I bought the car, but it never makes the sound when they test it. The dealer removed the wheel and brakes and said it could find nothing wrong. --V.L. Bedford Park.

A. You need to find a way to duplicate the sound when service personnel attempt to fix it. The noise could be coming from the suspension when the car moves up and down over bumps because of things such as a dried-out rubber suspension component or bushing. It also could be coming from an up-down wheel movement. It might help if someone sits in the backseat to check out the noise because sounds heard from the driver's seat could be coming from an area of the car a driver doesn't suspect. Some technicians even occasionally ride in the trunk to discover uncommon sounds. I own an old classic car that made a squeaking noise that occurred only when the auto was driven over certain types of bumps or rough pavement. It came from a deteriorating right rear shock absorber, which was silent when driven over most roads.

Q. What's wrong with continuing to fill my car's gas tank even after the pump makes a clicking sound that indicates the tank is full? I usually can add more fuel without it overflowing. --C.K., West Chicago

A. You'll eventually damage the car's evaporative emissions system, which will cost you money to correct.

Q. What's the point of filling a car with premium-grade gasoline? --F.K., Berwyn

A. Nearly all cars since the 1990s run fine on regular-grade 87-octane gasoline. Using regular-grade gas in high-performance cars with a high compression ratio such as a Chevrolet Corvette once was likely to cause expensive engine damage. But nearly all cars since the 1990s run fine on regular-grade fuel. Even those with higher compression ratios can safely use regular-grade fuel because of such things as fuel injection (instead of carburetors) and electronic controls that protect engines from a condition called "knocking." That was a rattling sound that was the result of out-of-control combustion, with the air-fuel mixture an engine uses burning erratically. Such combustion could severely damage an engine. But using a lower-grade fuel than recommended by an automaker results in a loss in performance because the engine then doesn't generate its full amount of horsepower.

Q. I hear you could get more fuel per dollar by filling a vehicle's gas tank early in the morning. Is that true? --A.J., Oak Park

A. Gas is sold by volume and expands with heat. But it doesn't help to buy gas early in the morning when the day generally is still cool, says Susan Garfield of the California Energy Commission. She says that's an "urban myth because fuel tanks act like thermos bottles, retaining heat." The only remedy is to install equipment that automatically adjusts fuel price to temperature. In fact, such automatic temperature compensation devices are attached to nearly every gas and diesel fuel pump in Canada. So far, legislative and regulatory proposals to mandate hot fuel compensation have gone nowhere on the national level in this country.

Car question? Send it to Dan Jedlicka, Chicago Sun-Times, 350 N. Orleans, Chicago, IL 60654, or e-mail djedlicka@suntimes.com. Include name, hometown and a self-addressed, stamped envelope to ensure a personal reply.