Does running on almost-empty damage the catalytic converter?

Dear Car Talk

Dear Car Talk | Mar 01, 1993

Dear Tom and Ray:

I really enjoy reading your column and thank you for the valuable information which I share with other family members. I have a question I don't think you've ever answered. It seems that our fuel gauge registers empty long before we really need to refill the tank. I was told that it is engineered that way because the catalytic converter/emission control devices demand that the car never run with less than four to five gallons in the tank. Is this information correct? I set my odometer every time I fill up with gas. And I know that the gauge reads empty at about 240 miles. But I know I can go at least 350 miles on a tankful. Other than taking a chance of running out of gas, is there any other damage being done to any part of the car by driving it with such a small amount of gas in the tank?

RAY: You know, Mae, it's about time someone put a stop to all these rank amateurs giving out incorrect car advice.

TOM: Right. That should be left to the professionals. If anyone's going to give out incorrect advice about cars, it's going to be us!

RAY: Actually, Mae, that story you heard about the catalytic converter needing four or five gallons of fuel is a bunch of baloney. The catalytic converter doesn't have the slightest idea how much gas is in the tank. In fact, the only part of the car that knows how much gas you have is the gas gauge. And it doesn't care how much you have in there either.

TOM: With the exception of a very small number of cars whose fuel pumps could be damaged by running the tank empty (your owner's manual would warn you of this), you won't hurt anything by driving around with the tank close to empty.

RAY: But it does sound like your gauge is very inaccurate. They're usually off by a few percent, and yours is off by much more than that. You could probably fix it by putting in a new fuel tank sending unit. But if I were you, I wouldn't bother. You've obviously got it down to a science.

TOM: So live dangerously, Mae. Run it down to fumes. But make sure you have a good pair of Nikes in the trunk...just in case.

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