Your Money

The Gas Gauge Says Full, But That's Not Quite True

  • Playlist
  • Download
  • Embed
    <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
  • Transcript

After filling your tank, your car's gas gauge may stay on full for a day or two before the needle starts creeping toward empty. That's because auto engineers have calibrated our gas gauges to lie to us. Host Scott Simon talks with Ford Motor Company engineer Phil Pierron about why the gauge is intentionally calibrated to be inaccurate.


Take a look at something the next time you fill up your gas tank. Your car's gas gauge may stay on full for a day or two before the needle starts creeping left towards empty. And thats because auto engineers have calibrated our gas gauges to lie to us.

Phil Pierron is an engineer at Ford and joins us on the phone from his office in Detroit.

Mr. Pierron, thanks so much for being with us.

Mr. PHIL PIERRON (Engineer, Ford Motor Company): Oh, you're welcome.

SIMON: Can you get into trouble spilling beans on this?

Mr. PIERRON: Well, I dont know that we're really spilling beans on anything. I think what we're actually doing is trying to convert our customers' wants and needs into, you know, an engineering requirement.

(Soundbite of laughter)

SIMON: How does not telling somebody how much gas they have left in their tanks serve their requirements? I mean because even if you want them to be hopeful and optimistic, at some point it runs out.

Mr. PIERRON: Yes, it does. And I think in reality, I think what we're trying to do is give a customer a prediction of when that will happen. But we're also trying to give him things that he's comfortable with. You know, for example, what you're describing about staying on full, from the engineering community, we call that a full reserve. And what does is when a customer goes and refuels, some customers - when the pump clicks off the first time, they stop refueling. Some will actually click several times after that.

So what we do is we need to assure that the gauge will read full at that first click, and also stays on full for an amount of time that the customer feels comfortable with.

SIMON: In other words, a gauge that would read full when it's not really. And, for that matter, empty when it's not really.

Mr. PIERRON: Yeah, the gauge will get to full at something a little less than the rated capacity of the tank. Now, youve probably seen in gauges also that the gauge typically can travel slightly past the full mark, as well.

SIMON: So why can we drive for a couple of days and it won't register?

Mr. PIERRON: Well, a couple of days might be a little exaggeration.

(Soundbite of laughter)

Mr. PIERRON: But again, it depends on the customer's usage patterns. We usually try and target, you know, probably around 20 or 30 miles, something in that range so that the gauge will make sure it updates.

SIMON: Is this in any way analogous as there is in the, let's say, the dress industry to size eights that are marked size four?

Mr. PIERRON: I dont think so because I think, you know, what we do print in the owner's manual is what the fuel tank actually can hold. You know, we'll tell what the actual usable capacity of the tank is.

SIMON: Mr. Pierron, you must be a real revelation to go on a road trip with.

(Soundbite of laughter)

Mr. PIERRON: Why would you say that?

SIMON: Well, I mean, you know, all - you know everything about the car. You know all the little tricks and all the little nuances.

Mr. PIERRON: Well, I dont know that it's such a revelation. I mean I think if you talk to a general customer, you can have him know that he'll say when he gets to empty, he knows he can drive still a little farther. And he knows that when his gauge is on full it's going to stay there for a bit. I mean there's even been Seinfeld episode where Kramer is driving and, you know, he's talking about how long he can drive on empty. So...

(Soundbite of laughter)

SIMON: Phil Pierron, an engineer at Ford, speaking with us from Detroit, thanks so much.

Mr. PIERRON: Oh, you're welcome.

SIMON: Fill yourself up, WEEKEND EDITION from NPR News.

Copyright © 2011 NPR. All rights reserved. Visit our website terms of use and permissions pages at for further information.

NPR transcripts are created on a rush deadline by a contractor for NPR, and accuracy and availability may vary. This text may not be in its final form and may be updated or revised in the future. Please be aware that the authoritative record of NPR’s programming is the audio.



Please keep your community civil. All comments must follow the Community rules and terms of use, and will be moderated prior to posting. NPR reserves the right to use the comments we receive, in whole or in part, and to use the commenter's name and location, in any medium. See also the Terms of Use, Privacy Policy and Community FAQ.

NPR thanks our sponsors

Become an NPR sponsor

Support comes from