NO fix for Prius Gas Tank Filling Up Issues

No, I don't. Even if I try, it doesn't take any more fuel. The problem with the nozzle seal is that gasoline flowing in somewhat pressurizes the bladder because the vapor flow rate through the vapor recovery system is somewhat restricted. Thus, the bladder is stretched larger due to the pressure (more than just the weight of the gasoline alone would do). So, when the fuel nozzle is removed and the extra pressure thus released, the bladder shrinks some and "burps" the gas on the ground.

 

I cut it out using an Exacto knife, holding the loosened portion with long-nose pliers so that the rubber wouldn't fall into the tank. But even if it does, it should not cause any problems; the pump suction screen will stop it.

 

eestlane, could you take of pic of that operation and post it in this thread?

 

Sorry, its all gone-gone! Actually, not much to see. Just look into the gas-fill hole and you'll see the rubber seal at the beginning of the pipe leading to the tank. Reach in and cut around it partially, then grab the loose end with long nose pliers, and cut the rest of the way. If a small piece falls into the tank, not to worry.

 

Ok, finally I understand, you don't necessarly care about how much fuel you put in the tank, but about checking the calibration of the MPG guage(s). So you want to know true distance and true fuel transfer into your car.

Here's my thought, and please don't take this as argumentative back-talk. How many of the potential error sources are you prepared to deal with? Can you independently measure distance, time, and fuel transfer to high enough accuracy? Clearly fuel transfer to the car is not consistent, based on the guage in the car. How accurate is the guage on the pump? Would it need to be accurate for regulatory purposes, or merely consistent for every pump in the country. Don't be mislead to assume that a display to thousandths of a gallon translates to that level of accuracy. Old mechanical pump meters showed tenths of gallons, with no reason to believe they were even that accurate.

distance: Can you or will you attach a fifth wheel sensor to your car? Standard GPS ON MOVING PLATFORMS) is not accurate below 50 to 100 meters, depending on your definition of "accurate."

Time it the only easy one.

IMO, it's not a reasonable expectation to challenge the calibration of the OEM guage, based on standard driving and pump guage fuel metering. Car engineers do it based on measured road distances and pre-measured amounts of fuel supply. In other words, for example drive a known 50-mile track supplied by a precisely measured two gallons of fuel, and when finished measure the amount of residual fuel. BTW, test track fuel is standardized, commercial pump gasoline is not. How do you compare this result to similar trials done elsewhere, at different temperatures, or with different terrain? Well, those are the next problems.

 

eestlane--I think you are on to something with your rubber gasket removal. If that's the fix, I can understand why Toyota wouldn't implement it--they would probably lose their low emissions rating. By the way, perhaps the same result can be obtained by leaving the gasket in place and bypassing it with a straw or small diameter piece of tubing inserted with the filler nozzle each time you fill up. I might do some experimenting along those lines--the idea of removing the rubber gasket does not appeal to me. Thanks for your inputs.

 

This point right here, I would think should concern anyone in California. I know when I get a smog check, the technician takes off the gas cap and does a visual check of everything including the gas-fill hole. It would really suck to have to buy, remove and install a bunch of parts just to replace that little rubber ring and pass a smog check.

Is this an issue? I don't know. But it sure seems worthy of some thought before cutting.

 

This is exactly what I was saying before. The Prius system is flawed. You said that perhaps the symptoms would show up with a Prius first. Other cars out there have as good or even better emissions ratings than the Prius and don't have the problem at all. Why should other manufacturers screw up their cars like the Prius? Why doesn't Toyota just do like the other manufacturers that can meet the emissions ratings without the bladder? This is mainly what I was referring to when I talked about denying there is a flaw.

 

Sure, there are other ways to do it. The Gen I Prius didn't use the bladder, but there were some additional complications because of that.

You keep hammering on the flaw. Do you understand my point about it not being a flaw for all of us that never have trouble with refueling? It would be equally valid for me to say you keep making up all this stuff about a problem when there isn't any. I won't say that because I believe that some owners have refueling problems. You should also acknowledge that many Prius owners do not have refueling problems. It goes both ways.

Tom

 

It is interesting that it happens EVERY fill up. To minimize this problem, I always use the slowest pump speed possible while filling up. This gives more time to allow the bladder to respond elastically and stretch more. It also can give the rubber time to warm up if the gas is coming from in-ground tanks, and warm rubber stretches better allowing more gas to get into the bladder.

It won't solve the issue, but if you are always filling up at the maximum pump speed, you are making the bladder size problem worse.

Toyota is not going to tell you how to fill up your car, they are too polite and you are the customer, so you must be right (even if you aren't).

 

I have a 2008 Prius and the only issue that I'm having is I fill up the gas tank too Full on F and as soon as i leave the gas station gas on Full goes down then back up too Full and it drives me nuts sooo I have to take it to the dealer for the 3 time so they can do a check with a computer and fill the prius up on a full tank of gas so i have to bring it in on low fuel and this time they better find what it is wrong with it and fix it / but that is the only issue that i have with it everything else is great soo far .

 

I always use the slowest speed possible. It doesn't always stop the problem but I do know how to get around it if it does.

WOW! Who knew there would be another symptom unique only to the Prius and the fuel tank fiasco called the bladder? I really hope the '10 doesn't have this "unique"(read PITA) feature too.

 

Tom, just because you or I do not experience the problem does not mean the flaw doesn't exist. There are some flaws that result in almost universal failure, some that are only partial, and some that are intermittent. The gas tank problems aren't due the user, they are due to flaws in design (and possibly manufacture/assembly) of an unnecessarily complex tank system. If say 10 or 20% of users can't reliably fill their tanks because of the design then it is flawed.

Sometimes when doing plant design folks would be intent on avoiding various problems by introducing all sorts of automatic trips, shutdowns, and delays and I became a devil's advocate in limiting them to a reasonable number. They were forgetting that you have to be able to make the system run. One of the things I had learned operating such things is that if you make some simple aspects too complex then a process is tough to keep running even when things are fine. (And start ups become really hairy...because of systems intended to protect things...and before long multiple protections are being bypassed just to get things running.) So I became careful in design to apply the KISS principle whenever possible. The Prius bladder system won't pass such a review.

 

Agreed. Now go back and reread what I have posted. My point is that the OP insists that those of us without the problem are in denial. That's not the case - we simply do not have the problem. I would like to see the OP admit this fact.

The KISS system is good. I made a living for a lot of years as an automation engineer, and spent a lot of time an effort designing systems to be used by automation engineers. There is also another good quote in this area, this one paraphrased from Einstein: "Everything should be as simple as possible, but no simpler."

Tom

 

Shawn--Well put and right on. The Prius fuel tank design is flawed. My informal, word of mouth survey of Prius owners I run into, indicates that appx. 60% of us are experiencing the problem.

Qbee--You post often, and I find your posts very helpful in increasing my technical knowledge of the Prius (thanks)--except on this topic. You apparently do not experience the problem, yet go to great lengths in discussing why it is not a problem. I think, with your backround, if you assume the problem exists (as reported by many on this site), you can come up with some analysis which can help us all understand what is going on. Please take this as a constructive suggestion. Thanks again.

 

I have already done that, although I will repost here so that you don't have to look for it. Like all modern cars, the Prius uses a sealed gas tank assembly to keep fuel vapors from leaking into the air. Venting is done through a charcoal canister. Unlike most other cars, the Prius has a seal at the filler opening, which prevents fuel vapors from sneaking out when refueling. Because other cars don't have this, some locations require vapor recovery systems on refueling nozzles, which are essentially a vacuum system around the filler nozzle which sucks in escaping fumes. Most locations, like where we live, simply allow these fumes to escape into the air.

In addition to this filler seal, the Prius also uses a bladder in the fuel tank to minimize the generation of fuel vapor. In a normal fuel tank there is a pocket of free air at the top of the tank. This air is saturated with fuel vapor. Temperature and barometric changes cause this air to expand and push fuel vapor out of the tank vent. The vapor recovery canister will attempt to recover this fuel and keep it from escaping, but its job is made harder by the large amount of free air. The bladder in the Prius fuel tank replaces this free air, which keeps fuel vapors from forming.

The bladder and filler seal are both good ideas, unfortunately they cause refueling problems for some owners. The problems fall into two groups:

1) Premature click-off - The bladder and filler seal act together as a big balloon, trapping pressure inside of the fuel tank. There is a vent designed to relieve some of this pressure, but some of it is inherent to the design of the bladder. This back pressure can fool the auto-shutoff feature of the filler nozzle, causing early shut off during refueling.

2) Belching gas - This is really a variation of the pressure problem. If the pump nozzle does not click off properly, additional fuel will be squeezed into the tank. With a normal gas tank this fuel would back up the filler nozzle during refueling, either causing the nozzle to click off, or giving the tell-tail sound of overfilling. In some cases the gas would overflow. With the Prius, the filler seal prevents the gas from coming out the filler tube. Instead the overfill pressurizes the bladder, which causes gas to burp out when the nozzle is removed.

Neither one of these problems will occur with a properly adjusted filler nozzle. Unfortunately the adjustment is pickier for the Prius than for standard cars, so a poorly adjusted nozzle may work okay for normal cars but cause problems with a Prius.

We can't control nozzle adjustment, other than changing pumps, so let's look at the other factors:

1) The Prius fuel system uses a complicated system of valves. Depending on the need, these valves are used for normal operation, refueling, and testing. The Prius must be powered off for the valves to be in the refueling mode. Filling while powered is asking for problems. A problem with the valve system could cause refueling trouble, but I would expect some sort of error code if this happens.

2) Temperature changes the characteristics of the bladder. Colder weather reduces the elasticity, causing a reduction of net volume. Bladder elasticity may also vary from Prius to Prius, but this is speculation.

3) The specified capacity of the Prius fuel tank is 11.9 gallons. This, of course, is absolute rubbish, and is the source of much frustration. The gross capacity is 11.9 gallons, but the usable capacity is closer to 10 gallons. It would save a lot of frustration if this were clearly stated in the specifications.

4) Refueling technique varies from one owner to the next. Some of the trouble is self inflicted from topping off and high speed filling. Note that I am not saying that all of the trouble is from that. I am just noting that some owners get what they deserve from using poor or unapproved techniques.

As for me, I have clearly stated over and over that I don't have this problem with my Prius. That doesn't mean that others are lying, it simply means I don't have this problem. As for the number of owners with this problem, they aren't as large as the previous post suggests. While unscientific, a poll on PC showed that 1.75% always have trouble while 59.06% never have trouble. The entire poll is on this thread:

http://priuschat.com/forums/care-ma...-refueling-problem-poll-all-prius-owners.html

I hope this helps, and I hope that readers are objective enough to realize that I am not denying the existence of the refueling problem, but only trying to put it in perspective.

Tom

 

Last January, I attempted my very first fillup on my new 2008 prius. The tank had been down to 1 pip, so I was shocked when the pump clicked off at 4.5 gallons. Having delt with similar issues before, I pulled back the fuel vapor boot on the pump nozzel, carefully removed the fill nozzel from the car's fill hole, and listened for pressure release sounds--there were none to be heard. I put the nozzel back in, as with any other car, but held the boot back to keep any vapor pressure from developing within the nozzel's fuel vapor recovery system (this technique has worked with every other car I've owned). The nozzel immediately clicked off after about 0.5 gallons (this has never happened with any other car of mine, and in fact never happened even plastic gas containers). Based on my experience filling those red, plastic gas cans, I know that the instant the liquid fuel touches the end of the fill nozzel, the pump shuts off, regardless of vapor pressure in the tank. So, I pulled out the nozzel and looked for gas in the car's Fill Pipe--there was none. Tried to pump again--click! Again--click! At that point, I decided that 5.5 gallons was probably enough fuel for the time being. That was the incident that caused me to search for PriusChat for the very first time.

On the next fill up, I was down to 2 pips. At a different gas station, I attempted to pump fuel as with any other car--put the nozzel in such that it locked into the fill hole, rotated the nozzel a bit to be sure the rubber seal actually sealed correctly, and then fueled at full speed. Absolutely no problems whatsoever. It's been nearly a year, and even traveling cross country, I've had no problems (even when the tank took more gas during the summer months . . . scary). So in retrospect, the problem sure did seem like an intermittent type of problem with the car, perhaps due to some sort of valve sticking closed or something.

Upon studying the Prius fuel system (PDF posted by Kar Idea on Page 6 of this thread), I see there are a number of valves that come into play during refueling. When fuel enters the bladder, it expands within the outer metal tank. The resulting air pressure must be vented through the Trap Filter, the Canister Closed Valve, and the Fresh Air Valve to the atmosphere while the bladder expands. If any one of these components works incorrectly, pressure will build up in the outer metal tank during fueling. Meanwhile, any fuel vapor generated within the bladder during normal refueling must be vented throught the EVAP system, then through the above listed valves, and then to the atmosphere. The EVAP system includes the Fuel Check Valve and the Refuel Check Valve. There is also a Vapor Pressure Sensor on the outer metal tank which ultimately ties in with the Charcoal Canister. If any one of these components malfunctions during refueling, pressure may build up either in the outer metal tank and/or in the bladder. In each case, fuel could back up into the Filler Pipe.

Now, another question, which isn't apparent in the above-mentioned PDF, is whether or not there's some sort of "one-way valve" within the Filler Pipe to the bladder? If not, then I would expect any pressure due to normal expansion of the bladder must be pretty low; if the bladder balloons, fuel is seriously going to blow out of the Filler Pipe. Assuming that normal bladder-expansion pressure is faily low, I am led back to the performance of any of the above-listed valves. If any one of them hangs, you'll get above-normal pressure buildup within the outer metal tank and/or the bladder, both leading to refueling problems.

 

I keep a record of every fillup. I print out the receipt and note the number of pips and the miles since the last fillup on the receipt. I also keep a small notebook where I note the indicated gas mileage and the number of gallons of fuel added. I then calculate the gas mileage the old fashioned way and note that as well. I understand that the calculated mileage is in itself a meaningless figure but if the calculated figure is less than the indicated figure I believe that I may have filled to what I call a "higher percentage of potential capacity" than previously. I have had three occasions where I could only put in 1.5 gallons into a tank where I should have been able to put in at least 7 or so gallons. On those occasions I took it to the dealer. On one occasion they just ran a scan and then filled it up. On the second occasion they did something called "recalibrating the inclinometers" which supposedly fixed the problem. Interestingly, the Toyota service literature says to do this if the customer complains about not being able to fill the tank. My understanding of the purpose of the inclinometers (which measure how far off from level the car is) is to keep you from overfilling and getting gas in the evaporation canister if you are filling on a steep incline, which actually never happens. On the third occasion (at a different dealer as I was out of town) they also just ran the scan and were unable to reproduce the problem.

I agree that it is a definite nuisance. Many times the pump clicks off well before you think it should. Even if you can fill it up somewhat you don't really know how far you can go before you have to fill it up again. For me a fillup is always a moment of high drama. How much gas will I be able to get into the tank? I would like to go across the Southwest but I am hesitant to do so because I envision being in some isolated place and only being able to get a gallon and a half in the tank. Whom did you write to at Toyota? I would love to do so as well. I suspect that it could be fixed in software. It is a glaring detraction from a vehicle that is in most other respects an engineering masterpiece.

 

FWIW I never heard of such a thing as "improper refueling technique" until I ran into this problem on my Prius. I often fill up very slowly, manually holding the lever on the filler nozzle so it will deliver at low speed. Still it often clicks off about a gallon or so below what I think it should. You may ask what I mean by how much I think it should take. I base that on how many pips are showing and how far I've gone since I filled up. I have a rule of thumb of one gallon per pip which I admit may be high. That is, a pip may actually represent less than a gallon. I am aware of the bladder gas tank and that the gas tank is a complicated system (overly so, in my opinion). Sometimes, if I am not going on a long trip, I fill up as one would a normal car, that is, I hook the nozzle on the tank, set the automatic shutoff, and let fly, just to see what will happen. I don't consider this to be "improper" technique. I keep extensive data on how many pips are showing, how much gas I put in, and how many miles I've gone since the last fillup in case you are interested. I don't keep data on which pump at which station I've used but I've encountered issues at several different pumps at different stations.

 

I dare someone to say that this doesn't make the bladder a dangerous safety issue.