Q Here's a short freeway-driving question. I understand the concept of "slower moving traffic keep right" and driving "with the flow." On a three-lane freeway, can a driver travel at the speed limit in the center lane?

My preference is to avoid the right lane with its merging decisions, and I'd never think of holding up the flow by driving the speed limit in the left lane. May I travel, without guilt, at the posted speed in the center lane, assuming it's not bumper-to-bumper rush hour?

A Of course you can. By law, you can -- and should -- drive the speed limit in any lane. Your awareness of courtesy and traffic flow will help you make the right decision about what speed to drive and which lane to drive in.

You raise that somewhat awkward equation of "speed limit" vs. "traffic flow." In fact, the most controversial Motoring column I've ever written was titled -- in jest, of course -- "Left-Lane Bandits." The column attempted to make light of those motorists who occupy the left lane at or below the speed limit to "enforce" traffic law and control the speeds of fellow motorists. In contrast, of course, to those motorists who flash headlights, tailgate and otherwise try to intimidate slower left-lane motorists to move over and let them by.

The most interesting aspect of that column is that it generated more than 500 letters to me -- split almost precisely 50/50. I even received a written threat to "short brake" me on the freeway to pitch me through my windshield. I was stunned by the response, realized that I had apparently touched a very sensitive nerve, and wore a disguise in public for several months.

The column was written in the mid-1980s when traffic still flowed well in the metro area. Imagine the response it would create today!

My answer, as it has always been, is to suggest that lane courtesy be the driving force in your metro freeway travels. When driving conditions are relatively congestion-free, drive at the speed you're comfortable with and stay right except to pass. On a freeway with three or more lanes of travel in each direction, feel free to use the middle lane for your "through" driving -- just be willing to move to the right lane to allow a faster vehicle to pass safely. On a four-lane freeway with two lanes of travel in each direction, keep it simple. Stay in the right lane except to pass, and if you're in the left lane, move to the right lane to allow a faster vehicle to pass safely.

Q I have a 1995 Buick Century with a 3.1-liter engine. It just turned 100,000 miles and still runs great. I have kept it well-maintained and had the radiator flushed last fall for $75. In January, the heater started acting up and throwing cold air, and the temperature needle would go to the top. Sometimes this happens when starting and other times after running well -- and all of sudden cold air.

During the past few months I've had two mechanics check it. I've gotten a new radiator cap, thermostat and water pump, and had the radiator and heater core flushed again. But it still acts up. The mechanics have said it is the head gaskets and probably warped heads. The repair cost is between $1,000 and $1,500. The car is not worth much more than that. What is your opinion?

A The symptom you're experiencing is caused by air trapped in the cooling system. When the bubble reaches the water pump, the pump can't circulate coolant. Coolant flow stops momentarily, the temperature gauge climbs and no heat comes from the heater outlets. Once the bubble passes and the pump starts pumping again, the gauge drops back toward normal and the heater starts working again.

The question is: Where is the bubble coming from? Low coolant level can cause this, so make sure there are no leaks anywhere, including from the two-piece intake manifold and gaskets. And of course, head-gasket failure can force combustion/exhaust gases into the coolant, generating the bubble that stalls coolant flow. The best test for this is to have the coolant checked for hydrocarbons in the exhaust. Any significant contamination is a significant problem.

You could try adding a quality "stop-leak" product such as Mendtite to the cooling system. It's very effective, and it might buy you many more trouble-free miles before having to deal with this issue again.

Is the vehicle worth a $1,500 repair? Probably not, for the simple reason that the additional investment in dollars won't increase its value, it will only allow you to continue to drive the vehicle. That money might be better spent on a newer vehicle.

If it were mine, I'd try the Mendtite and cross my fingers.