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The Prius Geyser

Good luck getting Toyota to own up to the problem. This is the company that responded to a rash of unintended-acceleration complaints with the new slogan “Toyota: Moving Forward”.

The original text summary of this call to Car Talk incorrectly summarizes the problem.

The problem is NOT related to trying to “TOP OFF” a Prius gas tank which implies the driver is trying to put EXTRA fuel in the tank after the pump automatically clicks off.

I have this problem and it occurs on the Prius when the driver tries to fill the car and removes the gas pump hose after it clicks off the first time. The hose clicks off the first time indicating the tank is full, the driver removes the filler hose, and gas begins to burp out of the Prius on to the ground.

Hi, just wanted to add my two cents. I downloaded the last fifty episodes of Car Talk and just came across this episode yesterday. I, too, have the same problem. I do use the SAME gas station every time, so it is NOT the gas station. I have a 2008 Prius and although the manual says it takes 11.4 gallons, I have never been able to add more than 8 gallons. I rarely let it get down to less than two bars on the gauge though so this seemed reasonable. I have kept it on the automatic flow (which I will no longer do) and it has always shut off after 6, 7 or 8 gallons. One day, it shut off at 9.3 gallons. I never heard any gurgling and no gas spewed out while this was filling. So I placed it back into the pump and thought everything was fine. But I heard this burping kind of sound and then the geyser began. It must have flowed out for at least two minutes. Horrible. Gas everywhere. I went to the Toyota dealership and of course they had never heard of such a thing. THey were also afraid that the extra gas must have gone into the tank that holds the charcoal. They said I would get a “check engine” light and it would need to be replaced for $600. I never got the light and this hasn’t happened since. I will be sure not to put the automatic lever on. I have also made sure not to put more than 7-8 gallons in. So glad Anne called in.

Talk about a solution in search of a problem!

To save a truly miniscule release of fuel vapor on fill-up (when everything works correctly), the Prius uses a collapsible fuel tank that–on occasion–dumps significant quantities of raw fuel on the ground.

I just wonder how often this system has to malfunction for it to be a net “bad thing,” enviro-wise.

Reminds me of the “new, greener” gas jerry cans that (to save a tiny bit of vapor release) do away with the vent hole. This means that–in actual practice–it’s almost impossible to pour gas without spilling a substantial amount of it, negating (and then some) whatever eco savings were sought.

Unless gas pump handles have been redesigned recently, the automatic shut-off mechanism in a pump handle works by sensing that a rise in gasoline level has covered the sensor port(s) at the end of the pump spout. At least that was true as late as 2005.

A Bernoulli-effect vacuum is caused by the gasoline flowing though the flow constricting, spring-loaded, one-way check valve (not identified in the diagram below) at the start of the spout. The valve seat of this conical, one-way check valve is drilled with transverse holes and is labeled the “Venturi ring” in the diagram. The transverse holes deliver the vacuum created by the Bernoulli effect from inside to the outside of the valve seat. Outside the Venturi ring (or valve seat) are vacuum passage-ways to (1) a small internal vacuum tube that lies within the spout, and to (2) a vacuum chamber which lies above a flexible diaphragm further back in the handle.

When the rising gasoline covers the sensor port(s) at the end of the spout, the Bernoulli vacuum can no longer bleed off through the small vacuum tube inside the spout. Instead the Bernoulli vacuum pulls air from the vacuum chamber that lies above the flexible diaphragm. The diaphragm then moves upward, releasing the automatic shut-off mechanism below.

Toyota has fixed these problems in the current generation of Prius (starting in 2010) by deleting the d**med gas tank bladder which was used in prior generations of North American Prii.

One problem is that one can not put gas in the tank with certain nozzles. Many report turning the nozzle upside down allows gasoline to be delivered.

The bladder is essentially a balloon. Inflate it too much and it will spray back. Or once its filled its a bit stiff in the first place and might take a few moments to start settling. If one doesn’t have the gas cap in place when the folds start expanding then it can very well spit a gallon of gas back out at you due to the turbulence in the tank.

Maybe this is related but I just don’t get it. I recently took my 2003 Prius in for the major regular service. I entered with half a tank of gas. I had filled it up about 5 days earlier. When I picked up the car 5 hours later and turned it on it registered “add fuel” on the screen and was at the lowest bar and the little light next to it was blinking. Looked like no gas. The dealer explained about the bladder, but also said the car would turn off if there was no gas. They took it to a nearby gas station and of course there WAS half a tank. I’ve had this car since it was new and never saw this before.
My questions: Was it something to do with the service that caused this? Will it happen out of the blue again? (they said something about it sitting - but I let it sit for over 5 hours ALL THE TIME). Will the engine shut off out of the blue if it THINKS it it out of gas?