Fuel Tank issues

Well regardless of what anybody has said here and I'm not sure what happened to your dad what kind of car did he have Not a generation 2 Prius correct? The generation 2 Prius gas tank is built like a well tank the blue thing out in the country that you have connected to your water well pump before the water goes into your house your gas tank is built just like that in the Prius It has a bladder in it when you fill the gas tank the gas you're putting in the tank stretches a bladder a big piece of rubber skin like material and when that bladder is stretched it pushes down on the fuel helps push it out of the tank and through the pump so that there's no air mixed with the fuel in the tank so that doesn't out gas into atmosphere. The same car in the United Kingdom does not have this bladder in the gas tank I'm sure there's a reason for it. I bet I can get 12 gallons in your gas tank. I started with the same problem you have right now with the Prius I bought like 4 years ago almost five now now it can fill on high and it shuts off at 8 gallons and I squeeze off at half speed the last three taking me right around 11 gallons which is in the exact same car you have. Does your speedometer always work but does it ever go blank? You have any codes in your car's system like communication codes for the gateway or anything like that would you know it if you did have? I only ask these things because there is probably a little more to the story The bladder in the tank can be stretched out by adding gas slowly until it starts to burp out of the tank literally if you think this is backing up your charcoal canister or going to cause you more grief than not then that is a belief that you have to deal with. What kind of car was your dad topping off that's my only question to you at this point. I've been topping off my tank since the gas crisis in 1973 so there's always that and I mean I feel the sucker up until it's running down the filler neck body panel I wipe it with my towel cap it off and go almost 500 mi and then we're filling up when we're as close to fumes as I think I need to be this speedometer and the trip meter still work perfectly.

 

Lots of people have heard there is a bladder inside a US Gen 1 or Gen 2 fuel tank, so lots of people having refueling issues jump to "because bladder something something" as an explanation of the issue.

All those cars in the US came with the bladder, and all of them came able to be fueled. There are some minor annoyances that really can be pinned on the bladder ... tank doesn't always take quite the same amount on a fill, takes less on a fill in cold weather than in warm, that sort of thing. Those are minor annoyances, not "stops after a few gallons and spews fuel out" issues. When you have those kinds of issues, something else is going on.

The big difference between a Prius bladder tank and a well water pressure tank is that the well tank is sealed on the other side of its bladder. There is trapped air there, so pumping water in expands the bladder and compresses the air, and that trapped air pressure is what squeezes the bladder back down and gives you water when you open the faucet.

None of that is true about the Prius bladder tank. The space outside the bladder is vented to atmospheric pressure (through the evaporative emissions and onboard-refueling vapor recovery plumbing) and so should never be building up pressure or vacuum. (The car runs occasional self tests where it closes off some valves and then checks that it can build up a vacuum, just for the duration of the test, to detect any leaks.) The bladder just helps ensure that the air freely leaving and entering the tank isn't mixed with fuel vapor.



When that system starts really malfunctioning—not just the normal run-of-the-mill slight annoyances because of the bladder, but really stopping at a small fraction of capacity and/or spewing fuel back out—it's generally telling you something in that air/vapor plumbing isn't passing air, and needs to be fixed. A history of topping-off will be part of the story a lot of the time.

Our classic PriusChat thread on the issue involved somebody who, about five weeks into the thread, posted "I am confident to say the the problem is resolved" after replacement of a couple of valves in the ORVR system.

But the same person ignored repeated advice, given in that thread, to stop topping off—and started a brand new thread eight months later for the same problem again.

 

Another possibility is that your fuel gauge is flat out lying to you. 3 of the 4 Gen2 fuel tank replacements that I have done were for bad level sensors. Yours could have a worn spot at 4 gallons down. That would trigger the low fuel warning while you actually have 5 or 6 gallons left

The sensor should have around 4 ohms resistance at "full" and 110 ohms at "empty". Anything over that (like 200 ohms to mega-ohms or an open circuit) reads as "empty".

You can wait until the "add fuel" message comes on then pop the rear seat bottom out. Remove the access panel toward the left side, then test sensor resistance per the service manual in the "Meter" section

Posted via the PriusChat mobile app.

 

Directly beneath you if you're sitting in the rear seat, but it comes out more easily if you're not.

It's secured at its forward edge by clips that will pop out if you give that front edge a good determined yoink.

Then it just lifts forward and out.

 

I think the overfilling problem with the gas tanks and most vehicles not just Toyotas is when you fill up the vehicle and you run it all the way up to filler tube and it goes down that overflow tube that's at the very top of the filler neck usually and you continuously do that you wind up filling the evap system and charcoal canister up with fuel. Generally the charcoal canister is just to take vapors off of the fuel set them in the canister and then those vapors get sucked back into the engine when the solenoid at the back of the car opens and commands that those fumes be sucked out of the evap or charcoal canister system If you continuously fill the charcoal canister and never let it rest then it's going to be sucking more than vapor out of the charcoal canister but once it does that it will dry that charcoal canister out pretty quickly. My motorcycles have this exact same problem it's noted in the owner's manual I can see a hose that goes to my charcoal canister in my bike and when I see fuel get halfway into that hose by looking at the hose while I'm standing there feeling the bike I stopped feeling the bike. Soon as I start said like I can see that hose that's got fuel in it that's heading to the charcoal canister that line clears almost immediately at startup. Course you can't see that in the Prius but that's what I think is happening when the gas spits back at you. Anyway I've gone from filling my tank when I bought the car with six or seven gallons to the gas blowing back at me to where now I can come in at empty the dot flashing I can put about 10.1 in it now very quickly too. So I guess the bladder has stretched out some or gotten back to its original pliability or what have you.