Hamilton Journal-News

Dear Tom and Ray:

I drive a 2002 Subaru Outback. During this past winter, we had a significant cold snap where I live, with temperatures below zero. After the first day of the cold snap, I noticed a puddle of coolant on the floor of my garage. So I visited a local mechanic who specializes in radiators. He attached some sort of pressure gadget and pumped it up. According to him, there was no indication of a leak. He looked around a bit — without crawling underneath the vehicle — and said he just wasn't sure there was a problem. So, he topped off the coolant and I returned home. Everything was fine, until we had our next cold snap. Once again, I noticed a puddle of gooey green stuff. Now that the weather is warmer, it's fine again. What's going on? — Vicky

RAY: I'm guessing that whatever it is, Vicky, it's caused by shrinkage. We know things shrink when they're cold, right? (See also: George Costanza.)

TOM: If it's something serious, it will eventually start to leak regardless of the temperature.

RAY: My first guess would be a loose hose clamp. The rubber coolant hoses are clamped onto metal fittings under the hood, and there are lots of them. If one of those hose clamps is just barely tight enough, and that fitting is shrinking in the extreme cold, that could be enough to allow some coolant to leak out.

TOM: Then, when the temperature rises and the fitting expands back to its normal size, everything's fine again.

RAY: Of course, it could be something much more lugubrious, like a failing water pump, or even a bad head gasket.

TOM: But here's where we'd start. First, have your guy check it again with the engine cold. You'll need to leave it overnight so he can pressurize it first thing in the morning, before the engine has run. If a pressure test on a cold engine turns up nothing, then I'd have him check and tighten all of your hose clamps, including the ones that feed the heater.

RAY: And then keep an eye on it. See if there's any more coolant on the garage floor. If it starts leaking in more normal weather, then it should get easier to diagnose, and your mechanic can even add some dye to the coolant to help him find the source of the leak.

TOM: But once he realizes you're not expecting him to chill his shop down to minus 6 degrees to get the leak to happen, he may be more willing to spend a little time helping you figure this out. Good luck, Vicky.

How long can you drive after fuel light comes on?

Dear Tom and Ray:

My husband freaks out if the gas light ever comes on (it only happens once in a blue moon). I tell him you can drive around 50 miles after the light comes on. He doesn't believe me. Since we don't want to actually test my theory and risk being stuck without gas, I thought I'd write and ask you guys what you think. So? — Liesa

RAY: Well, there certainly is SOME margin for error built into fuel gauges. How much varies from car to car. But I'd guess that the average low-fuel light comes on when you have about an eighth of a tank left.

TOM: There are two ways to find out whether that's true for your car, Liesa. You already know one way. You drive until you run out of gas, walk 50 miles home, and then say, "Honey, I told you!"

RAY: But there's an easier way to figure it out. Go to the back of your owner's manual and, in the "specifications" section, look up "fuel capacity." Let's say your gas tank holds 16 gallons.

TOM: Then, with your husband not in the car (no need to unnecessarily drive up his blood pressure), drive until the low-fuel light comes on. Then go to a gas station and fill the tank all the way up.

RAY: Now, subtract the amount the tank took from your fuel tank capacity. In other words, if the tank holds 16 gallons, and you just filled it up all the way with 14 gallons, you know there are two gallons in reserve when the light comes on.

TOM: You may want to run this experiment several times to maximize your data and minimize the measurement error.

RAY: Now, how far will that remaining gasoline take you? It depends on the actual quantity of gas, your gas mileage, and what kind of driving you're doing.

TOM: But you know that however many miles you can go until empty, your husband will still be freaking out. Some people are just less inclined to enjoy surprises. Especially when they involve getting stranded and passing through the digestive systems of wolves.

RAY: So, for his sake, fill it up before the light comes on. Or, at least, soon after. Don't torture the poor guy, Liesa — as enjoyable as that may sometimes be.

Send your comments or questions for Tom and Ray to: Car Talk Plaza, P.O. Box 3500 Harvard Square, Cambridge, MA 02238. Visit them on the Internet at www.cartalk.com.