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The Prius Geyser

What happens when you top off a Prius? For Anne in Los Angeles, the answer is your little hybrid turns into an ungrateful automotive gasoline geyser. Her ‘08 Prius shoots gas back out the filler tube, over the side of the car… and all over Anne. (Hear the call right here.)

Tom and Ray suspected that she was not alone, and that a technical service bulletin might soon be in the offing. The problem could be related to the Prius’ special rubber-bladder gas tank, which has been known to be stubborn during cold weather.

In the meantime, Tom and Ray thought she’ll just have to grin and bear the backsplash, or head to a full-service gas station every time she wants to fill up.

We wanted to hear from other Prius owners. Have you had this experience? Know a Prius owner who has? If so, share your experience right here – with the rest of the Car Talk Community… and with fuel-soaked Anne.

On behalf of other gas-drenched Prius owners, thanks!

First of all, I don’t own a Prius, but I do drive one for work. For a couple years there was no issue with this, but in the past six months it has come up in several locations. I work for the state, and some of the state gas pumps were recently changed, and this problem began to occur. This has happened on multiple occassions, so I believe it has something to do with the Prius filling/angle, just not working with the newer pumps. Anne may need to find particular gas stations which have pumps that don’t give her a problem. Glad I don’t own one!

My husband and I have two Prius’s, (yes, I know).

The same terrifying event happened to me, once. I was filling up at a gas station that I never used before. I followed every proceedure I normally follow, which I don’t think is different than the proceedures anyone else uses (of course, I could be wrong). As the tank reached full it made a funny noise, which I now know was the gas filling beyond the normal cut-off point. I was staring quizzically at the nozzel when the gas started pouring down the side of my car. I was terribly startled but managed to yank the nozzle out of the opening, (less than gracefully, I am sure).

When I got home I rinsed the car off and went into a state of mourning for my poor Prius, which obviously had developed some awful reflux problem.

But…the good news!

I never went back to that gas station and the problem never happened again.

I blame the gas station.

Love your show!! Listen every week.


It might be the gas station. People are creatures of habit so they tend to use the same gas stations, and sometimes the same pump. It would have been worth asking her if it always happened at the same gas station.

I was a gas jockey for years and some cars do this more than others. It’s probably not just one thing, but a combination of things, usually starting with basic design - like the angle on the filler tube at the upper neck, or where it enters the tank. The canister system can also be a problem, not doing it’s job because of similar design issue. But it can also have the added factor that during manufacture that the filler tube, canister lines, vent tube (anything in the filling system that handles fuel, air, or fumes, was bent just so, or twisted, or pinched just enough, that it won’t let the system vent properly, so fuel backs up, and then any trapped air in the tank and/or filler tube will get explosive car-diarrhea.

Sometimes you can minimize the backwash by putting the nozzle tip just barely into the filler hole, as this let some air behind the gas to seep in, but even so it will usually happen to some degree. The best way is to do that and listen for the gurgling sound that says gas is starting to back up and let go of the nozzle trigger ASAP. It might backwash a bit, but it’ll be a dribble compared to a blue whale breaching for air. Do NOT use the trigger lock when pumping gas! It’s convenient, with the auto-shutoff feature, but no matter what notch you use (even the slowest), gas will jet back out.

The Isuzu Trooper II was notorious for this. It didn’t matter how slow you tried to pump the gas in it would blow back out. There were a rare few that didn’t, but the owners were well aware of it. Some new owners would ask that we make sure that gas didn’t discharge, but we’d have to give them the “Trooper II” lecture. Some idiots would get out and use the glass cleaner and squeeze we had in a bucket to wipe the gas off the car and we’d see shiny new metal gleaming where there used to be paint, then try to sue us for their idiocy. Just use some paper towels to GENTLY blot the gas off, then use some water and car wash detergent to clean it off when you get home.

The only fix is going to be through the factory TSB fix. Toyota knows what’s what here. Best bet is to find other Prius owners with this problem and contact Toyota en mass. If you have a Prius owner with that problem that happens to be a lawyer, cop, or judge, so much the better. That’s what it took for the local Isuzu dealer to make it right, when one of my regular customers in a Trooper II was a cop and I showed him the issue.

Tom and Ray, you have let us all down. We thought you knew EVERYTHING about EVERY car on the road and a bunch that no longer exist.

  1. You failed to ask the ONLY question needed to lead you to the right answer:
    Do you always fill at the same gas station?
    Given she said it happened only 3 times, her answer would have been: NO
  2. You figured the Prius tank holds about 10 gallons so if it got close to that it would over fill. The 2004 and later Prius holds 11.9 gallons. I only put in less than 10.5 to 11 gallons if I am going on a trip.

As you noted (though you said MAY have!!), the 2004-2009 Prius has a bladder, like a balloon, in the gas tank that collapses as the gas is used so there is no space for fumes to build up (environmental protection). It also doesn’t allow water vapor to build up so no worries with vapor lock in the winter if you don’t keep your tank half full (or whatever the suggestion is with other cars). This bladder causes back pressure as it expands, more when the car was quite new and in the winter when the cold makes the material less flexible. Anne’s experience is not unknown but actually opposite what most Gen II Prius owners complain about - that the pump shuts off BEFORE the tank is filled.

The problem Anne is having is not a problem with the car, thus no TSB is needed, but with the pump which is why the dealer can’t find a problem. But they are at fault for not informing her of the mechanism by which her problem can occur. The pump is not properly registering the back pressure and shutting off. It over expands the bladder which then contracts once the pressure lets off. The only way this can happen with a pump that is working properly is to force gas in a tiny bit at a time as the pump shuts off every < .05 gallons. Most 2004-2009 Prius owners have the opposite problem with pumps that are too sensitive to back pressure and they have to ‘eek in’ the final gallon or two.

Two solutions to Anne’s problem:

  1. Use stations where she knows this does not happen.
  2. Calculate how much gas she will need before filling. It is easy since the Prius will reset the ‘tank average MPG’ on the multifunction display when she fills (pretty much anything over about 4 gallons). If she also resets trip A or B at the same time, simple division will let her know that it will take 8.5, 9.4, 10.8 or whatever the next time. If the pump gets to that point and doesn’t shut off, time to take matters into her own hands and stop the pump.

#2 is better as she can still buy gas where the price is lowest. If she always fills the tank instead of putting in $X dollars, she can confidently know how much gas she has used, and thus put in, every time she gets gas.

Unlike ivyvine (who is glad to not own a Prius) there is no car in the world you could give me to replace my Prius.

Bruce Alvarez
Owner (and admitted rabid Prius enthusiast) of a 2004 and a 2006 Prius

I’ve also shared Anne’s experience. I have filled my Prius several times at the same station, and once last winter after the pump shut off, the car burped a fair amount of gas on my shoes and down the side of the car. It has never happened again. I’m stumped.
I agree that full service gas stations are what we need. I refused to fill my tank at a self serve station for about 20 years, requiring my husband to get gas for me. I finally broke down and started pumping my own gas again a couple years ago, and I hate it. I miss those nice fellows who would also clean your windshield and check the oil.

one more reason for not buying a Prius

Yes all American 2004 thru 2009 (Generation 2 cars), and maybe those prior to 2004 also (Generation 1 cars), have a fuel bladder inside the metal tank. The 2010 and newer cars (Generation 3) no longer have the bladder. It was discontinued because it frequently will not fill to capacity in the winter and because overfilling can get gas between the bladder and metal tank and cause serious problems.

I have not had the over flow problem with my 2005 Prius in the 25K miles I have owned it. However, according to this can happen in a few circumstances. 1). This happens most often when topping off the tank after the initial auto shutoff. Do not top off the tank. I live in Oregon and topping off is illegal here and has been for about a year or two. 2). Faulty gas station pumps cause this problem. The auto shutoff is trigger by back pressure. It the sensor is bad the back pressure will not be detected. If the pump is filling extremely slowly, there will not be enough back pressure to trigger the sensor. 3). Trying to fill the tank when the Prius is not off. It has to be off to set the valves in the evaporative emission system to the right venting for filling. If the car is on, but the gasoline engine is not running (ready mode), the tank will not fill correctly and may overflow.

Of course, it may be possible for the Prius venting valves to malfunction. However, the owners, including Toyota technicians, indicate that the above three reasons account for the vast majority of the overflows.

I have this problem–not with a Prius, but with a Jeep Wrangler. I remember reading that the theory is currently that the higher amounts of ethanol that gasoline now contains is the culprit. They did eventually issue a TSB and it can be fixed by replacing the fuel tank ventilation hose. Good luck!

Simple. This is the result of over-filling, too fast.

(I’ve assumed air is trapped inside while the fuel is filled on top of the compressed air bubble, and gas is added without allowing time or space for the air to escape. I may be wrong on that, but the exact mechanism does not matter.)

Solutions : Don’t top-off to to the max. Toward the max, fill very slowly and with the nozzle slightly retracted to allow air to escape. Or, leave the rubber nozzle seal in place when stopped pumping very full, and retract very slightly and push back to let a burp of air to escape while preventing gas spurting out, then repeat until all trapped air has gently escaped.

We’ve had gas spew out after filling our Prius a couple of times. The pump shut off and when we pulled out the gas nozzle, gas came gushing back out. At other times we have had trouble getting any but a tiny amount of gas in even when we know it is low on gas. Trying to put in a little at a time didn’t work. Both are frustrating and we possible solutions to this puzzler! By the way, the spewing occurred in warm weather the cold weather theory would not explain all incidents, we never top off the fuel tank, and we never leave the car on when filling. We have not had either happen for a while now so are wondering if it was a problem pump as bruceha_2000 explained. We’ll keep track of where it happens from now on.

We had an expensive headlight replacement which is a problem Toyota needs to address. We had to get the more expensive headlights to get the navigation system. They are not as good as other headlights I’ve had even though they cost many times as much and the replacement cost was ridiculous. I had better headlights in a little Tracker which were inexpensive and easy to replace yourself.

Even with that one expensive repair, the Prius is reliable, gets great mileage and is fun to drive. Love the sound system and would buy it again.

I had a 1984 Toyota with the same problem from the day my family bought it new. It was a crink in the vent system that required pulling the tank to fix. My zero cost solution was to put 8 gallons and not a bit more in whenever I got down to a quarter tank. Can’t use the deadman’s switch, and you have to watch the pump, but in the grand scheme of things, a minor inconvenience. My brother had a Ford with the same problem, from the first day he owned it. All I can figure is that something must have happened in transit to the dealers.
I’m just really surprised that Click and Clack didn’t zero right in on this, since it would seem to be not uncomoon.

We are Prius owners also with the filling the gas tank issue your caller asked about. It’s like the bladder inflates and if you pump in too much gas in, the air in the tank pressurizes. If you remove the nozzle, the air blows the gas back out. If you leave the nozzle in when this starts happening or pull it almost out, it’s like the air will bleed out or bubble out and the gas won’t spill out. This is true the FIRST time when you put too much gas in when you fill the tank. If after bleeding the air out of the tank the first time, if you continue putting more gas in, it will spill out anyway but if you quit pumping gas after the first time, let the air bleed out, the gas “probably” won’t spill out. To get a FULL tank with a Prius, you have to pump VERY SLOWLY after getting 9 gallons in a near empty tank.

Spraying gasoline is an extreme fire/explosion hazard. Any spark, static electricity or other source of ignition will cause serious injury to anybody near-by. Any car owner experiencing this problem should insist that either the service station or car maker fix the problem. In the mean time extreme care should be exercised or don’t fill the car.

Don’t blame the fueler or the pump when it is a design problem. there are numerous owners with Prius (gen2) fueling problems including me. Mine shuts off repeatedly no matter how slow I fill it, and has also overflowed. The tank not only includes the bladder (no longer in the gen3- wonder why? too many problems, of course) but the tank is also very shallow- and thus very sensitive to the sensors which indicate ‘full’. Bullitans inform techs that they need to have it on an extremely level surface to test the sensors.
Furthermore, the gas gauge is frequently inaccurate. often called the ‘gas guess’.
As for not topping off- when you can’t squeeze gas in the vehicle, it’s very difficult to know if you are topping it off! Essentially, you must calculate how much gas is left in the tank using the trip odometer and mpg on that tank, then add LESS than the amount to make a completely full tank - to avoid the backsplash. RIDICULOUS for a supposedly high tech vehicle.

It’s never the pump. They can’t be too sensitive, it’s a “dumb” technology they use to shut off, so there’s no faulty sensor to go bad. Having a “professional” gas jockey do it doesn’t solve the problem, other than now the gas pukes on them and not on your Sunday best. The design is bad, or something is plugged or twisted that won’t let air vent properly.

I have a 2005 Prius and the day before I heard the show, I had the same thing happen. It never goes past 9.5 gallons in filling up, and this time it was closer to 10.5 gallons. I took the hose out and, Mt Vesuvius!!! Very nice. All over my clothes and shoes. And it is the second time it has happened, though at a different gas station.

I own a 2007 Prius and have never had this particular issue but believe it is very similar to another common problem I have: The pump won’t pump. The Prius filler neck has a seal which forms around the pump nozzle sealing the junction. Some pumps have an overly sensitive back pressure valve and will not put fuel in a Prius. No doubt if some are too sensitive there are others which are not sensitive enough.

If Anne can reproduce the problem at a particular pump I suspect she could slip a plastic coffee stirring stick/straw between the nozzle and rubber seal to relieve the pressure allowing the nozzle to operate same as for a conventional gas tank. But its much easier to find another pump/station that works without hassle.

Perhaps I should also mention that I always run the pump on the slowest setting. For my usual 6 to 8 gallon purchase pumping gas any faster doesn’t save more than a few seconds. Heck, for some reason I do the same pumping 28 gallons of diesel in my F250, possibly because diesel foams if poured violently.

Toyota needs to address this issue and find a solution before someone is seriously injured. Toyota has a history of ignoring customer safety issues until someone is injured or killed, then start a PR campaign to convince the public they care.

On another note, the Prius is thought of as an environmentally friendly vehicle, but there is nothing environmentally friendly about one pint of spilled gasoline times the thousands of Generation 2 Priuses on the road.

As a Generation 2 Prius owner I have had the same issue. I’m not filling up wrong or too fast. A vehicle manufacturer has an obligation to deliver a safe vehicle to consumers. Being able to fill up that vehicle with gasoline should not require any user adjustment, long discussions on chat boards, or only filling the tank half way.

This is a dangerous situation. Toyota knows about it and ignores it like they have a history of doing including the situations where Toyota owners have been killed because of Toyota’s arrogance. Let’s hope Toyota doesn’t wait this one out until someone is seriously injured or worse in a fire and then tries to cover their tracks with an expensive PR campaign.