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I have read a few accounts of "stuffing" the tank, and can't find much on it aside from the obligatory "omgz don't overfill a Prius!!11!" warning. I did find the fuel system technical PDF at PC, which is helpful in figuring out what's going on. But I'd like someone who has thought this through (Dan and Larry?) to confirm or deny my understanding of how to get more than 8 gallons into the thing.

It looks to me like there are two potential routes for liquid fuel to get into the charcoal canister, causing damage and an expensive repair.
1) The EVAP line from the secondary tank (where the fuel sender is).
2) The EVAP line that ends at the top of the filler neck, a few inches below the rubber gasket.


Thus, there seem to be two things that the operator can do to force liquid fuel to go where it shouldn't be.
1) Force fuel under pressure (either with a broken pump or by "clicking" over and over and over again) into the tank, which would drive it up either one of those lines and into the canister.
2) Trickle fuel in (by withdrawing the nozzle above the gasket) in order to fill until the fuel level in the pipe is well above the top of the tank.

#1 I'm not so worried about, since I don't click over and over again and I know a broken pump as soon as I see more than about 8 gallons on the screen.

#2 is a different story since I presume this is the method used by some of you folks with success. What on earth prevents fuel getting in the canister? Given that it sits directly on top of the tank it could be hours or days before the fuel level falls completely below its level, and gravity doesn't take any time off!

Any enlightenment from the pros?

I only stuff if i'm going for a long distance tank....it justs takes to long to do it right. I guess i've used #2 till i could see i couldn't get any more in there.

I was kinda worried about this when i went for my 1K tank but a few people said they have been stuffing since day 1 so i took a chance.

this is a little off topic but i wonder if anyone has ever replaced the bladder tank with the Japanese tank. Doesn't it hold around 15 gallons and this woudn't be such an issue. I guess if you wan't to do this shipping a gas tank would be expensive.

Yeah, I just chanced it. figured I'd get a code if the EVAP went south

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Ironically, I wound up with an accidental "overfill" yesterday. I filled early to beat the hurricane price hike, and the pump didn't shut off. The first sign of trouble was the sound of vapor rushing past the gasket and the smell of gasoline! (The fact that it's strange to smell gasoline does give one an appreciation for the emissions controls.) I had to stuff the nozzle back in to prevent a backsplash but managed to avoid it. So far no issues, though I will be using a different pump next time.

Coincidentally, I discovered the gas gauge reset procedure and set the inclinometers back to zero before I filled. It would be nice if a mis-calibrated gauge were the only problem, though I fear that's a bit optimistic.

Coincidentally, I discovered the gas gauge reset procedure and set the inclinometers back to zero before I filled. It would be nice if a mis-calibrated gauge were the only problem, though I fear that's a bit optimistic.What is this reset procedure of which you speak?

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1) Park the car an a DEAD LEVEL surface with the tank between 1/4 and 3/4 full. The level surface is critical because this is your baseline.
2) In IG-On, cycle the odometer to Trip A. (You don't need to go to "Ready" for this procedure.)
3) Power off the car.
4) While holding down the Trip/ODO button, power the car to IG-ON.
5) One the car is booted, cycle the Trip/ODO button as follows:
Release-Press-Release-Press-Release-HOLD.
If you did this step right, you will be looking at the odometer at the end.
6) While holding the button, the odometer will change to a bunch of seemingly random numbers and/or letters. (I think I saw 060606, others at PC report a different sequence.) You may see these numbers change, indicating that calibration is taking place. 10 or 15 seconds ought to be more than enough.

Hi Tim:

___Very interesting procedure. Now what does it do again as I have never felt the need to perform this in the Press or others Prius'? Does the gauge stick at ½ or 2/3 when you are full and it needs to be reset :confused:

___Good Luck

___Wayne

My understanding is that the Prius calculates fuel level based on two things: the float in the secondary tank and the angle at which the car sits. The purpose of the angle compensation is to keep the bars from jumping around as you drive up and down hills, which would be maddening.

So let's say that the inclinometers are miscalibrated such that the car thinks that a level road is actually down-hill. Assuming that the float is at the front of the tank (I think that's right?) the computer would compensate for the false grade by reducing the indicated level. Thus, you believe that you have less fuel than you actually do. The result would be reduced driving range because you always fill when you actually have fuel left. If the gauge were miscalibrated the other way, you could run out of fuel unexpectedly.

Both conditions have been reported by Prius owners, and this is how the Toyota techs are instructed to fix it. I am rarely able to gen more than 8 gallons (usually 7-ish) in the car even when I run it down to one pip, so it seems worth a shot.