Why are gas gauges different for every manufacturer?

Dear Car Talk

Dear Car Talk | Feb 01, 1995

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 half way 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?

TOM: 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.

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