Dear Tom and Ray: Why do different car manufacturers set such different standards on their gas gauges? In our old Buick, when the needle hit the yellow area, you had to be driving into a gas station with enough momentum to reach the pumps or you were in trouble. On our new Taurus, you can drive for another week.
Also, why does the first half of the tank take so long to run out while the second half flies? On my Blazer, I find that I can get about 220 miles on a tank before the gauge hits the halfway mark. But the second half of the tank is gone within another 150 miles. Finally, what's an easy way to learn the real size of your gas tank? - HarryTOM: Good questions, Harry. The reason the gauge says Empty before the tank is actually empty is that the manufacturers don't trust you. They build in a little "wiggle room" to make sure you don't actually run out of gas.
RAY: In the old days, it didn't matter. You ran out of gas? Tough! But modern cars have fuel pumps that are submerged inside their gas tanks. And since the gasoline acts as their lubricant and coolant, you can do damage to the fuel pump if you run the tank dry. So the manufacturers make sure that even when the gauge reads Empty, you still have a little gas left.
TOM: That's also why the first half of the tank appears to last longer than the second half of the tank. It's because you never actually use all of the second half of the tank. When the needle gets to Empty, there's still gasoline in there. And, as we just explained, it's there for a good reason.
RAY: So, given this information, what's an easy way to determine the actual size of your gas tank? Well, you sound like the curious fellow, Harry. I'm sure that our explanation has merely piqued your interest. And I know you're going to run the tank in your Taurus down past empty, just to see how much gas is really in there.
TOM: And that's how you'll find out how big the tank is. When you run out of gas, see how much it takes to fill it back up. Then you can sit down and think about your new-found information . . . while they're putting in your new fuel pump.
Dear Tom and Ray: It was my understanding that spoilers are used to increase high-speed traction on the drive wheels of a car. That being the case, what is the purpose of a spoiler on the rear of a front-wheel-drive car? - Barry
RAY: The main purpose of spoilers is getting dates, Barry. Of course, it's never worked for me, even though I've had a spoiler on the back of my '87 Dodge Dakota pickup truck for years.
TOM: Theoretically, spoilers do serve a marginally useful purpose. They're designed to use the wind - when the car is traveling at high speed - to force the rear end of the car downward. That's supposed to help keep the rear wheels planted more firmly on the pavement, which helps you maintain traction.
RAY: And the reason that's useful, even with front-wheel drive, is that no matter which wheels are powered by the engine, it's still a good idea to have all four wheels on the ground - Jim Rockford notwithstanding. Even if you're driving a front-wheel-drive car, you want those rear wheels firmly on the ground for cornering, braking and just plain stability.
TOM: But the truth is, at 55 or 65 miles an hour, spoilers don't do much. They're designed for race cars that take corners at 120 miles an hour, speeds at which wheels can actually start to lift off the ground. And in those situations, they can really make a difference. But in day-to-day driving, they serve the same societal purpose as tattoos and hair replacements.
The Magliozzi brothers' radio show "Car Talk" can be heard each Saturday at 10 a.m. on KUER FM 90.1 If you have a question about cars, write to Click and Clack Talk Cars c/o King Features Syndicate, 235 E. 45th St., New York, NY 10017.