Accuracy of 2004 Prius gas gauge

[ian721]

Anyone else have a beef with the accuracy of the gas gauge on a 2004 Prius? When my 04's gauge is on the last light it will only take around 8.5 gallons into its 11.9 gallon tank.

Today, with only 4 of the ten lights lit, the computer indicated that I had used less than 5 gallons since the last fillup (that's miles since the last fillup/avg. mpg in that same time). If that's so, then it should have had something more like 6 lights lit. I've tried running it down to where the last light is blinking and it still only takes less than 9 gallons.

Something's not quite right here. Seems like the gas gauge is too low. Lots of trips to the gas station more than necessary.

[Tideland Prius]

ah yes, the old fuel tank/gas gauge question.

First of all, the Prius' fuel tank is equipped with a flexible rubber bladder. This bladder collapses as fuel is used eliminating the possibility of vapour forming inside of the gas tank. This helps earn its AT-PZEV rating which is a SULEV rating PLUS zero evaporative emission. Now, because we have this bladder in the tank, we can't use the old "low fuel light means I have 10 litres left" trick that we can use on other Toyotas. Also, with lower ambient temperature, the bladder will hold even less fuel (can't remember the exact figure but it's in the owner's manual).

The most I've pumped is 37 litres or about 9.79 gals. That was on my record tank of 836kms (522.5mi).

In short, I wouldn't worry about it.

[ian721]

I had a feeling this came up before but I had trouble searching because the site was acting funny the day I posted (which is why I accidentally started 4 threads on the same subject).

Thanks for the explanation about the bladder (it's a company car and I didn't read the manual like I did with my Camry), but I still don't see why the gauge can't be more accurate. The most I've ever pumped is ~8.5 gallons. Last week I let it run around 25 miles past when the light started blinking and it only took 8.2 gallons.

I wasn' t nervous because the trip computer is accurate and with minor calculations you know exactly how much gas you're used since the last time it was reset (which I do every time I fill up). But now that I know about the bladder I actually am a little nervous. I wish I knew what was in the tank after a fillup. The specs say 11.9 gallons, which would mean that the gas gauge is grossly inaccurate and I should just go by the trip computer.

I was prepared to ignore the gas gauge and just the trip computer calculations. So is the gauge accurate or not?


(Pardon my lack of metric conversion, but you know us dumbass Americans don't care about that stuff Besides, you seem more than capable.)

[Tideland Prius]

no problem

I don't think the gas gauge is inaccurate in the sense that there's fuel left but more like if it says it's low, it really means that you'll "run out of fuel" in the sense that the car won't suck any more from the tank. Now if you've read the Prius Marathon thread, you saw that they had the low fuel light blinking for 9 hrs+ lol.

So, a couple of things, if you really wanted to test it out, by all means but it the engine shuts off, I wouldn't recommend driving on battery unless you stop across the intersection from a gas station. True, it'd be nice to get the 600 mile range that owners in other countries without the bladder get, but 500 miles in the summer is pretty good for me. The bladder shrinks in cold weather (-30°C it's about 38 litres instead of 45 litres (so abt 2 gal lost)

I can give you a rough guideline but don't quote me on it. If you have 4.8L/100km or better.. so that's..49? mpg, then you have ~60 miles on the blinking light before you get into the danger of running out of fuel zone. That's in the summer.

[ian721]

I only got 49 mpg once, on a long hiway trip through upstate New York. I don't own the car and I don't pay for insurance, gas, maintenance or repairs, so I drive it like a banshee through NYC traffic five days a week. I get around 37 mpg every tank. But thanks for the info.

[Tideland Prius]

np!

ya know, 49mpg on the highway ain't bad. I only got 46mpg doing 70mph with 4 ppl on board.

[ginostef]

Ian - there is a TSB for 2004 Prius that involves an inaccurate gauge and/or a fuel filler neck problem. I think it is TSB-0310, or something like that. Check out PriusChat.com and use their TSB lookup feature. Anyway - the gauge replacement and filler neck (not trivial replacement) is for a lot of early serial numbers, and the later serial numbers just has the filler neck replaced. It helped my 2004 (only the filler neck) in eliminating the slow bladder expansion (ie top off, top off, top off to get it filled) and that made the gauge more accurate. Clearly - in the cold, you will get about 1/2 gal less in the tank and you will have to be more patient. Goodl luck!