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Good morning! I was wondering if anyone else is having the same issue that I've been having.

My '04 Prius does not always fill up all the way when I go to the gas station. I've tried different stations to make sure it's not the pump. When I fill up, I usually let it go all the way to full and then reset the mileage calc. Sometimes I'll be all the way down to 1 bar of gas, and "fill up" with only 6 or so gallons. At first I thought that maybe the gauge was wrong, but I run out again after only about 300 miles instead of 500. So, there's definitely a problem with the tank or something.:confused:

Anybody have any ideas?

Thanks!
Andrea :D

Hi, Andrea!! You have stumbled upon an oft maligned characteristic of the US spec Prius -- the "bladder" tank.

Your fuel tank is actually a plastic bag inside of a metal container. Due to temperature/humidity/barometer/astronomic(JK!!!) variations the bag will not fill consistently. Sometimes you even end up with air bubbles in the bag preventing further fill...

Other Prius drivers here can chip in (I'm not one of them, unfortunately!), but the response I've mostly seen is -- "Sorry! That's the way it is. I don't like it either."

Good luck!

Your prius has a bladder tank and will take more fuel when it is warm outside, less when it's cold out. When I fill up, I will burp the bladder by wiggling the pump nossel. Then I can squeeze in another gallon or so. Your gas gauge is more of a "guess gauge" and does not reflect the true amount of fuel in the tank when close to or at full.

There's definitely the bladder to contend with. But only putting 6 gallons in (to first click?) when it's showing 1 bar on the "guess gauge" does seem a little low. Looking over my past data, I've put in as little as 7.1 to first click from 1 bar, but usually it's around 8.5. If you've had a sharp temperature drop lately (which would cause the bladder to contract a lot) I suppose 6 would be possible, or if the particular pump had a problem detecting when to shut off. I wouldn't be too worried, though. :)

This is something that tends to happen with the Prius. There's a flexible bladder in the tank to prevent fuel vaporization (to reduce emissions) and its true capacity varies with age and temperature. During the summer months I can get 9 or 10 gallons in there, in the winter I'm sometimes down to 6. Your mileage calc will always be off from tank to tank but it will be accurate over the long-run. The only thing you can really do is try to find pumps that work well with the tank and stick with them. Don't ever try to force more fuel into it because that presents a serious risk of the tank spitting fuel back at you, not to mention expensive damage to the fuel system. Many people have experienced the back splash and at least one that we know of has had to pay four figures for a new fuel tank due to repeated overfilling.

It helps to get gas in the afternoons when the temperatures are the warmest. When I fill up the Prius, I'll fill at the slowest rate possible until it clicks off. I'll remove the nozzle and wait a few seconds. I'll then put the nozzle just barely in the tank (imagine that it's like a mouse peeking out of a mouse hole to see if the cat is around). Then I'll fill again at a slow rate until it clicks off again. If it's more than a tenth of a gallon, or so, I'll repeat.

I can confirm it is cold weather related by the simple fact that it's never happened to me. ;)

Today it was an odd 38F on the way in, and I was feeling everyone's pain up north.

Go search for "overfill" at Priuschat and you'll shy away from putting in more than 10 gallons.

Does the owners' manual mention any of this about the Prius' fuel tank?

Your prius has a bladder tank and will take more fuel when it is warm outside, less when it's cold out. When I fill up, I will burp the bladder by wiggling the pump nossel. Then I can squeeze in another gallon or so. Your gas gauge is more of a "guess gauge" and does not reflect the true amount of fuel in the tank when close to or at full.I once filled up Dan's Prius and it burped due to my inexperience. :o

Early this year I joined PriusChat as Lisa Nowak (the "AstroNut" with the bad mug shot) and asked how I could get my Prius bladder to last 900 miles from Houston to Orlando. :D

Does the owners' manual mention any of this about the Prius' fuel tank?

Yes it does. I don't have it in front of me but there is a comment that the fuel capacity may be reduced by as much as 1 gallon in cold weather. For me, normally the pump shuts off at 6-7 gallons with one pip remaining. This issue could be worse for 2004 owners because in 2005 there was a TSB issued that would replace the filler tube IIRC in an attempt to make the issue less noticeable. I assume that 2005 and later models have this fix. I never bothered to have mine fixed.

I also have an original '04, and have only had one "burp"
[which got written up (http://techno-fandom.org/~hobbit/pix/ky07/part2.html)] because the pump shutoff was defective.
Otherwise I fill fairly slowly, and at the first clickoff stop
and shake the back end of the car around a bit to try and help
things settle down, and then try to round to the nearest dollar.
.
Note that if you don't insert the nozzle fully, you're possibly
DISABLING the auto-shutoff mechanism because it depends on that
little hole near the end of the nozzle to sense the space being
filled with fuel. You jam that against the filler gasket, you're
confusing the mechanism.
.
_H*