Gas Tank Mystery Solved?

I'm not sure that is a good idea. I heard somewhere that the Prius has an overfill protection that just runs excess gas back into the station tank. You think you are still fueling but are really just given money to the station and get no more gas in the tank. Is this an urban myth?

 

The stations have a vapor recovery system, so when you're overfilling, the excess fuel is being sucked into the recovery tank.

 

I don't know if that is an urban myth but I can tell you I use to overfill to the next $ for easy accounting on my monthly bill. One day when the fill up was some 10 cents over, I proceeded to top off. When I removed the nozzle, gas just gushed out of the tank. What a waste.

Then there's making the fuel pump work harder than it needs to in dry conditions inside the tank.

And there is the gas station caution about topping off and exposing liquid gas to the environment that just evaporates.

Nope, topping off is not recommended. It lets you drive longer on a tank but its costs more money and is hazardous if you get a faulty pump that lets you pump so much that it gushes back out.

 

An update.

Gas Pumps Go Naked As Vapor-Recovery Requirement Ends

 

but i thought the vapor recovery system in the cars could be damaged if you overfill?

 

Okay am i reading that article correctly? The vapor recovery system is a rubber boot at the end of the nozzle.

 

It's not a good idea to overfill the tank, fuel could be pushed through the EVAP system. Also, with the plug-in, the system has extra equipment and I wouldn't want to take a chance testing it with an overfill.

 

Around here, it was a boot around the nozzle and a hose that removed the fumes.

 

When you have a cup of coffee/tea, do you expect the level to be teetering at the edge of the cup?

 

If you buy beer at a pub in Britain, it had better be right to the rim of the glass or you're getting short measure. (Note that some glasses have a line instead).

But I don't top off my gas tank, here or there.

 

The same with our 2010 Prius. When the pump clicks off at slow speed I still can nurse in
another 2.1 gallons until the fuel is standing at the filler neck. When completely full
we have a true comfortable range of 450-500 miles even in winter.

Many state that this will damage the gas vapor recovery system in the Prius.
I checked the owners manual for our 2010 Prius and there is nothing
that I could find where it states not to fill up the tank to maximum.

How many in this forum have damaged their engine or other components
on their vehicle by filling up to maximum?

 

Pumping your own gas in Oregon?

 

Let me expand on that a little. The hose that removes the fumes is connected to the vent for the underground tank.
When you pump, say, 8 gallons of gasoline into your tank (if there isn't a vapor recovery system at the gas station) 8 gallons of gasoline vapor has to pour out of the filler neck to make room. Simultaneously, the underground station tank has to suck 8 gallons of air in to make up for what has been pumped out. The vapor recover systems simply connect one to the other--allow the underground tank to pull in the vapor from the filler neck to replace the pumped gasoline.

When a tanker truck is filling the underground tank you'll see two hoses in use, for the very same reason--so the thousands of gallons of gasoline don't push an equal volume of vapor out into the world.

 

As usual, I suspect that there are other facts not mentioned in the article about the vapor recovery "boot". As El Dobro and css28 say, the vapor recovery system in many parts of the country, like the urban areas of California, involves both the rubber seal AND a return hose to carry the vapors back to the service station's tank. It isn't just a seal to prevent vapors from getting out, like the article suggests, which could cause problems if the pressure builds up from vapors that have nowhere to go.

 

The bigger question is. . . How is it possible for a gas nozzle to shut off when there is still 2 gallons of space left? The tank is not an flexible bladder like the Series 2 right? The gas tank line can't hold two gallons. When I fill up my empty Prius I get nearly 10 gallons w/o nursing. What's with the two gallons? Exaggeration?

 

in what context are you asking this? in connection to which post? mine shuts off when full.

 

Decimal in the wrong place? 0.21 gal?

 

What he's saying is, for example, Totmacher claims to be able to put in two extra gallons after the pump shuts off at 8. Clearly the fuel line from the gas cap to the actual tank can't hold 2 gallons. So why does the pump shut off at 8, prematurely? Given that a) Gen 1 didn't have this problem and b) Gen 3 doesn't have the bladder like Gen 2 did?

 

I'm going to guess that it has to do with tank shape. If there's a large horizontal top surface (or even isolated pockets) it could take some burping to get extra fuel into it.

 

good question. i can't confirm it because i have always filled up when the last pip blinks. that's why i asked tot how many miles he drove past dte. another question would be, how does spending 3 minutes topping up an extra 2 gallons get you 300 extra miles of driving?