Overfilling the gas tank

Discussion in 'Gen 2 Prius Main Forum' started by SGM05Prius, Jul 29, 2008.

  1. SGM05Prius

    SGM05Prius New Member

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    I filled up on gas this morning and the gas pump malfunctioned - it didn't turn off automatically. Instead of the normal 9 to 9.5 gallons that my car will take right after my gas light comes on, I manually cut the pump off at 12.54 gallons, at which point the gas was pouring out the side of the gas tank onto the ground. I don't think more than a half gallon spilled on the ground...which means my tank somehow managed to hold 3 or so more gallons of gas than usual...is this going to harm my car some way?

    For the record, I did speak with someone at the dealer (not an actual mechanic, that seems an impossible thing to ask...) but the reply I got back from the service department manager was that it's no big deal. Then I called the mechanic I went to in my pre-Prius life (he just recently became certified to work on Priuses) - he also thought it was probably no big deal, especially since I managed to drive a half hour to work with no issues.

    But then... in the Technical Discussion forum in the thread about fuel bladders, there is a link to a Toyota Technical Training manual which says that overfilling the gas tank can force fuel into the EVAP system and damage system components, which completely contradicts what the dealership service department and my local mechanic told me.

    Any thoughts? Should I keep talking to mechanics, or not worry about it...since the car seems to be running fine.
     
  2. David Beale

    David Beale Senior Member

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    If you don't get a light you didn't cause any damage. The car will not "run poorly", you'll just get a light. There is a system in place to sense fuel between the tank and bladder and/or a leak in the bladder. It will throw a MIL/CEL or whatever you want to call it, indicating a code is stored for a problem.

    Even if you did cause damage (and it looks like you didn't), there is no point in worrying about it. There is nothing you can do about it. The "fix" for damaged system components is a new fuel tank, something only done after a light appears, the code is read, and after much head scratching the dealer tech. and others decide to replace the tank.

    The damage occurs -after- you fill the system to the top and let the fuel warm up (it's about 50-60 deg F in the underground tank). The fuel expands, worst case about 2-3 quarts, and forces its' way through the evap system, into the gap between the tank and bladder, perhaps even forcing a hose off its' fitting, or bursting the carbon canister (which is in the tank). This all happens because liquids are for the most part not compressible, whereas the gas "bubble" normally left at the top is. The gas bubble would compress absorbing the expansion of the fuel without producing undue pressure in the tank.
     
  3. SGM05Prius

    SGM05Prius New Member

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    Thanks! Would there be any reason to perhaps siphon some gas out of the tank so a hose doesn't pop off or something? I did drive about 20 miles (again with no lights coming on, no issues at all....). I should've used up a half gallon of gas doing that, easing the pressure somewhat. However it is also getting really hot today -about 95 degrees ...it just seems that there's a lot of potential for pressure to build up in all of this heat and possibly cause problems. Again, I know people top off their tanks, but this is about 3 gallons beyond where the pump would have normally cut off...

    On the other hand, I'm having a baby in a couple of weeks...I may just be hormonally geared up to worry for the sake of worrying....
     
  4. David Beale

    David Beale Senior Member

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    It is -very difficult- to siphon fuel out of a Prius. If you're really worried, make up a card to lay on the dash saying "Gas cap loose" and put it on the dash. Then loosen the gas cap. When you go to drive the car, tighten the gas cap and put the card away. Once you have burned about a gallon down from "absolutely full" there is nothing to worry about. Note that if you drive with the gas cap loose you WILL get a light (CEL or MIL). It will reset after a while once you tighten the gas cap (it may take a number of power on/off cycles, 3 as I recall). But a code will be stored that the dealer service guy will see. Also note that the fuel tank is not checked often, only every 3-5 uses of the car, as I recall. It's part of the carbon canister purge cycle.
     
  5. thepolarcrew

    thepolarcrew Senior Member

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    Does any one know the size of the external tank, as far as volume goes. I have had it down to 1 pip and filled over 11gal a couple of times.

    My thought would be, under the right conditions, the bladder would expand to this volume and it could be more than the 11.9? The stretch effect.
     
  6. steveholtam

    steveholtam Junior Member

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    This happened to me on my 08 about six months ago, twice, and didnt hurt anything, except the enviroment I guess. The first time I blamed the pump, the 2nd time I figured it was trhe car. I no longer do anything while pumping gas, except watch the gallons. After 10 gallons it normally auto-stops, but if not, I will stop it manually.

    I wouldnt worry about it.
     
  7. autoxic

    autoxic Commuter

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    The gas pump auto shut-off function can fail on any car. Usually, gas pumps shut off too early in a Prius. I guess it is a good idea to watch the pump for the one to two minutes it takes to fill up, right?

    Even 30 miles after the blinking pip, I rarely get more then 9 gallons in my 2004 Prius. I drive 550-600 miles per week, so I'd like to top off the tank each fill up, but I don't want to overfill. I hope the next Prius has a bigger gas tank; maybe 13.5 gallons.
     
  8. David Beale

    David Beale Senior Member

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    This is really funny. After posting this morning I went out to get groceries and fill the tank (just below 1/2). So of course it overfilled (nossle did not shut off). It attempted to burp out fuel, but I convinced it to burp vapour only (hold nossle and press down towards the ground, creating a gap in the seal above the nossle, where the vapour can escape). The fuel ended up at the filler - completely full. Put cap on, drove home (temp about 25C so lots of expansion would be expected). Of course I hit every red light, got behind every nit going slow. When I got home (5 km) I removed the cap - there was no fuel to be seen in the pipe. So if you overfill to the top and drive even a "short" distance (5 km is 3 mi) I suspect you would be fine. I left the cap loose (but sitting on the filler) just in case.

    BTW, I averaged 3.5 l/100 km on the way home according to the MFD, which is what I usually see from that station. The warmup cycle is a real hit to mileage, as my tank average is running around 4.6 l/100 km.
     
  9. qbee42

    qbee42 My other car is a boat

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    No, not possible. The tank is 11.9 U.S. gallons, and the bladder is completely contained inside that volume. The net capacity is therefor less than 11.9 gallons.

    Tom
     
  10. doubleg2005

    doubleg2005 Member

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    personally, the only times i've had this happen (twice) were when i took it down to a blinking pip... anytime i've filled up at 2 pips (usually) it takes about 8-8.5 gallons and has never *knocks on wood* overfilled.

    but, like i said, there were two times i took it down to a flashing pip and both times it overfilled... stupid bladder ;)
     
  11. abq sfr

    abq sfr New Member

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    BGT Syndrome, every Prius driver has experienced it at least once. I think the cause is the rubber seal that is against the filler pipe when filling. Some people have even cut that rubber seal:eek: Shut off at the first click, or sooner if you think it should already have clicked. You can go over 400 miles on a fillup with this car, what's another hundred miles worth to you, paying for a new fuel system?
     
  12. SGM05Prius

    SGM05Prius New Member

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    Huh, it's pretty interesting hearing hearing other people's experiences with overfilling....in 20 years of driving, yesterday was the first time I've ever had an overfill. And even though I go to different gas stations, the pumps are pretty consistent as far as reporting how much gas is going into the tank...I usually fill very soon after the last pip starts to blink, and I fairly consistently manage to put about 9.2 gallons in the tank in warm weather and about 10 gallons in coolish weather.

    Anyways, the woman at the gas station insisted that I pumped the gas wrong (that I put that little metal tab thingy that is on the nozzle on the wrong setting...)and that was why the tank overfilled, and i insisted that the pump was faulty, cause I've never overfilled before...I ended up reporting the station to the state agency that regulates oil spills and faulty gas pumps. I hope I didn't overreact....:confused:
     
  13. steveholtam

    steveholtam Junior Member

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    Yeah, I'd say you overreacted. I had the same exact thought until I read about it here. I am sure both my instances were the fault of the Prius, and not the pumps. Those pumps are used 100's of times every day. I've owned my car 6 months, and have only filled up like 14 times, and twice I had gas run out. It has not happened again since I now watch the filling process like a hawk.
     
  14. qbee42

    qbee42 My other car is a boat

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    I've had problems with other cars. It's not the Prius, although the Prius is more likely to have problems with a faulty pump. If the pump is properly adjusted, you will never have any trouble.

    Tom
     
  15. SGM05Prius

    SGM05Prius New Member

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    Well, now I have a light going on...it is the maintenance light, and it could be going on because I happen to be due for an oil change. Currently, it only flashes on and off a couple of times when I start the car and then stays off when I drive even though I'm 200 miles overdue for my oil change. Usually when I'm due for an oil change, it turns on right when I hit the mileage written on the oil change sticker in my windshield, and it stays on until the mechanic switches it off.
     
  16. eestlane

    eestlane Member

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    Cut away the rubber seal at the top of the filler pipe, and the Prius fuels just like any other car. No more under-fills, over-fills, burp-ups, getting fuel into the charcoal canister, etc. etc. Try it, you'll like it! The downside is a small quantity of gas fumes in the air, which is better than burping a few gallons on the ground.
     
  17. qbee42

    qbee42 My other car is a boat

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    The maintenance light is a simple mileage counter. It counts miles from the last time it was reset, and starts flashing to warn you of upcoming maintenance. It is not tied into the engine or any other system.

    Tom
     
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