Q. I read your advice in the March 19 AutoTimes about the use of regular and premium gasoline, and I agree with you. I add that General Motors' supercharged 3.8-liter V-6 it put in various late-model GM cars such as the Pontiac Grand Prix GTP, Chevrolet Monte Carlo SS and Buick Regal GS need premium fuel to prevent "knock" that can cause engine damage. --J.S., Hanover Park

A. As I noted, most cars run fine with regular-grade gasoline. And also that producers of some -- but not all -- high-performance models recommend premium fuel -- but allow use of regular-grade gas. However, they caution that it won't provide the performance of high-octane fuel. GM recommended premium fuel for that supercharged 3.8-liter V-6, used in fast cars. Always check the owner's manual to see what type fuel is allowed. Such information is occasionally put in the gas-filler area, especially if it's a high-performance model. Several years ago, I owned a 1965 Chevy Corvette with a 365-horsepower V-8 rebuilt to original specifications, and it started promptly and ran well only with leaded 100-plus octane gasoline, which is no longer available.

Q. I read your article about using regular grade gas in premium-fuel-recommended engines. My 1999 Buick Park Avenue Ultra has a supercharged V-6 that the owner's manual says should only use 90-plus-octane premium fuel. But when premium grade prices began rising, I switched to cheap premium gas from an off-brand station or mid-grade gas to save money. After about a month, the car got sluggish but recovered when I returned to a name-brand premium gas. When I switched to a cheaper grade again, the car began stalling. A Buick dealer said the gasoline was bad and had to be flushed out, and that I should only use premium fuel. I'm now afraid to to use anything but premium gasoline. Does my Buick really need it? --J.S., Chicago

A. The owner's manual likely recommends premium-only fuel because your car's supercharged 240-horsepower V-6 is a high- performance engine too old to have modern electronic engine controls that could allow it run smoothly with a lower-grade fuel. Also, it's best to buy name-brand gasoline. You can't be sure of exactly what you're getting when you buy an off-brand gas.

Q. I change my engine oil and filter every 3,000 miles. But from now on, I want to use synthetic oil. Should I also change it every 3,000 miles, or can I wait every four months or 4,000 miles? Is it OK to mix different brands of synthetic oil? --A.P., Glendale Heights

A. Mixing different brands of synthetic engine oil won't hurt. You can even mix synthetic oil with regular oil without doing harm, although that will cause you to lose advantages of synthetic oil, which can withstand extreme heat and cold better. Stick with your 3,000-mile oil change intervals, especially if you do lots of stop-go driving. Synthetic oil generally doesn't last longer than regular oil. It's costlier, and not necessary for regular Chicago-area driving.

Q. I just bought a 2001 four-cylinder Nissan Altima with an automatic transmission that was driven 147,00 miles. It looks practically new and runs very well. I realize the car has lots of mileage, but I would like to drive it as long as I can. What should I do to keep it running well and avoid problems? --R.K., McHenry

A. Such a high-mileage car usually doesn't look "practically new" unless it has good new paint, no rust and such things as a new interior, rubber moldings, etc. So congratulations. However, stay on top of it to keep it running well at that mileage, with regular oil changes and replacement of overly worn parts. Driving moderately also will help a lot.

Q. I want a Japanese all-wheel-drive SUV with great performance, low maintenance and good fuel economy. Among vehicles I like are the Toyota Highlander and Honda CR-V. --K.H., Chicago area

A. Those are sound choices, but getting "great performance" and what you might consider "good fuel economy" generally isn't possible in such a compact to mid-size SUV unless it's a costly hybrid, such as the Highlander Limited gas/electric Hybrid. It delivers an estimated 31 mpg in the city and 27 on highways. The CR-V has an economical four-cylinder gasoline engine, but it provides just average highway performance and only an estimated 20 mpg in the city, but 26 on highways. You might also consider the Japanese Toyota RAV4, Nissan Murano, Hyundai Santa Fe and Mitsubishi Outlander. But why just Japanese? Also look at such American SUVs as the new Dodge Journey, Ford Edge, Chevrolet Equinox and Pontiac Torrent.

Q. I'm about to buy a 1986 Honda Civic but was told there might have been a problem with this model "lunging" when sitting at, for instance, a traffic light. Heard of such a thing? I'd hate to buy the car and worry every time I stop behind someone, not knowing if I'll end up in their trunk. I've "googled" for information but can't find a word on that supposed problem. --R.S., Chicago area

A. Does the car lunge when you drive it? I haven't heard of such a problem with that model. If it existed, chances are Honda had its dealers take care of it long ago.

Q. I know there are only two Smart car dealerships in the Chicago area, but Smart doesn't advertise, so I don't know where they are! --N.F., Barrington

A. Smart says it's currently only using online advertising. But for those without a computer, here are this area's Smart dealerships: Smart Center Lake Bluff, 775 Rockland Road, Lake Bluff, and Smart Center Lincolnwood, 4255 W. Touhy Ave., Lincolnwood.

Car question? Send it to Dan Jedlicka, Chicago Sun-Times, 350 N. Orleans, Chicago 60654, or e-mail djedlicka@suntimes.com. Include name and hometown.