My gas gauge goes straight to empty when the tank reaches half-full.

Dear Car Talk

Dear Car Talk | Apr 01, 1998

Dear Tom and Ray:

I have a strange problem in my car, which, surprisingly, has improved my dating
life! My gas gauge goes straight to empty when the tank reaches half-full. So I
appear to have run out of gas a lot, which is a useful illusion on dates! Help.
I don't really want to fix it. I just want to know what's going on. -- David

TOM: David, you sly little devil, you! When you do figure out what causes this,
I suggest you immediately market it in college newspapers across the country.
You'll be a millionaire.

RAY: Actually, you probably just have a faulty gas tank sending unit, David.
There's a float in your gas tank that floats down as the fuel level drops. As
the float goes down, the metal contact attached to it slides down a variable
resistor. And the contact's point on that resistor tells your gas gauge how much
fuel is left. My guess is that the contact on that float/sending unit isn't
touching the bottom half of the resistor anymore.

TOM: It won't hurt anything if you leave it alone. But it will keep you from
knowing when you're really about to run out of gas -- which can be inconvenient.

RAY: Should you ever decide to fix it (you know, on the rare chance that someone
ever goes out with you more than once and catches on to your scheme), you can
have the sending unit in the gas tank replaced for somwhere between $100 and
$200. Have fun until then, David.

Get the Car Talk Newsletter

Got a question about your car?

Ask Someone Who Owns One