Dear Tom and Ray:

I felt the need to write to you about an answer you gave recently. A guy asked if one should keep the gas tank at least half-full in the winter to prevent gas-line freeze-up. You said "no," but then you made a comment about the real reason for keeping a tank full when it's cold: so that if you get stranded, you could keep the car running and the heat going. As an emergency physician, I need to point out that to do this when the exhaust is blocked in any way is to invite asphyxia by carbon monoxide -- probably not what you want to recommend to your readers. I think everyone could use a reminder. Thanks, and I enjoy your column. -- David

TOM: No, we certainly can't afford to lose any readers to asphyxiation, David. We lose enough of them to lousy answers and bad writing as it is.

RAY: Actually, we've addressed this before. But it can't hurt to mention it again. If you do get stuck in a snowstorm -- when snow is actually falling or being blown around -- you'll want to get out of your car every hour or so and make sure the area around the end of the exhaust pipe is good and clear.

TOM: If the pipe gets completely blocked up -- or even partially blocked -- and you have a leak in your exhaust system further up the line, you could end up with exhaust fumes coming in through the ventilation system. And that, as you say, David, is not a good thing.

RAY: We also recommend that if you're stuck and you don't know how long a rescue will take, you run the car, then shut it off for a while until you need heat again. This will make whatever gasoline you have last as long as possible.

TOM: But even better, observe our No. 1 rule of driving during snowstorms: don't. Call in sick and watch television. Pride yourself on being nonessential personnel. You'll be one less stranded motorist the rescuers need to worry about, and one more ratings point for "Columbo" reruns.