RAY: With the last name Sawyer?
TOM: We made that up, by the way, readers. Joey, I think your daughter has to try the experiment. And you need to be following her with a five-gallon gas container.
RAY: This car was still using a metal tank in 1998. So you crumpled it. But you probably didn’t deform it too badly; otherwise, it would be leaking now.
TOM: These tanks can take a pretty good beating. I mean, they’re not designed to support a 2,500-pound car on the saddle of a floor jack, but they do get hit by rocks and road debris and snow banks, and they manage to survive all that stuff.
RAY: What you need to find out is how much you’ve reduced the volume of the tank, and whether you’ve interfered with the operation of the float, which tells the gauge how much fuel is left. And there’s only one way to do that, Joey.
TOM: If you really wanted to be a good dad, you wouldn’t even make your daughter participate. You’d tap one of your buddies (who now knows what a bonehead you are because you wrote to us) and have him follow you while you drove your daughter’s car.
RAY: Here’s what you’ll do. This car has a tank that holds about 12 gallons. You know the gauge works fine between full and half-full, because you know that accounts for six gallons. You also know how many miles that gets you. Let’s say, for the sake of argument, that you get 150 miles out of the first half of the tank.
TOM: So you want to drive another 150 miles, or until the tank is empty. Along the way, you want to correlate the mileage with the reading on the fuel gauge.
RAY: So when you’ve driven 75 miles, is the gauge reading a quarter-full? If so, you know it’s accurate to the one-quarter mark.
TOM: If the car runs out of gas before you expect it to, you’ll want to note what happens. Did the gauge drop suddenly from a quarter-full to E? Did it stay on a quarter-full and just run out of gas?
RAY: And with this newfound, scientifically derived information, you’ll be able to tell your daughter exactly what to expect, and when she needs to fill up from now on.
TOM: And by the way, Joey, if the car runs out of gas as soon as you leave the house, you’ll know what you’re getting her for Christmas this year.
Switching oils is no big deal
Dear Tom and Ray: I have a 2009 Nissan Cube. I take the car to the dealer for oil changes. I always use synthetic, but at the last oil change, they put in regular oil by mistake. I drove the car for 3,000 miles and then asked them to put in synthetic oil. Now my husband says that I have “ruined” the engine by switching the oils back and forth. Is this true? He says that I immediately should have asked them to drain out the regular oil and replace it with synthetic before I drove the car away. What do you think? — Mary
TOM: I think he’s got his head up his oil drain, Mary.
RAY: When synthetic oils first came out, we heard rumors that you shouldn’t switch from regular oil to synthetic, or vice versa. But we never saw any proof that this was more than a rumor.
TOM: And now several of the major oil companies sell synthetic blends, which are what? Mixtures of regular oil and synthetic! So they mix them right at the factory.
RAY: So obviously, no harm is done by mixing them in your crankcase, or switching from one to another.
TOM: So drive happily, Mary. It sounds like the only thing you ruined here is your husband’s credibility.
Send your comments or questions for Tom and Ray to: Car Talk Plaza, P.O. Box 3500 Harvard Square, Cambridge, MA 02238. Listen to them Saturdays at 10 a.m. on 91.3 FM or 88.5 FM. Visit them on the Internet at www.cartalk.com.
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