Gas Fill Up question

I doubt anyone can fill it that full without the pressure of the bladder backing up and spilling out a cup or more of gasoline onto the ground (and cybele will tell you just how much environmental damage that will do!).

My suggestion is first, always, always set the pump to the lowest fill speed. Always.

Second, if you want more in the tank after the pump clicks off, give it a minute or so - clean the windshield, check the oil, etc. Then start to fill again, very slowly. Occasionally pull the nozzle all the way out of the opening - you'll probably hear gurgling as it's letting some air out from the pressure of the tank.

To put it simply, if you want more than 6-8 gallons in your tank, it takes patience and time and being careful not to spill any gas.

-m.

 

Filling to a consistent level (as for example, to the lip of the spout) is NOT, for the '04 Prius, a guarantee of accurate per-tank mpg, because you are actually filling the flexible bladder, and changes in the weather as well as aging of the bladder can change how much gas the tank will hold.

In addition, as mentioned above, you can wind up with gas spurting back onto the ground or onto you!

These differences from one tankful to the next, however, will average out, and if you calculate your mileage based on 5 or 10 tankfuls, the error due to differing fill amounts, will become insignificant.

Some folks have reported getting another gallon or so into the tank after the pump clicks off. Others have reported gas spurting out when they had only added half a gallon or less after the pump shut off.

Conclusion: add more gas only at your own risk!!!

 

Trying to pack in every last cupful of gas not only risks spillage, an obvious waste and source of air pollution, but saturates the vapor recovery system and further contributes to pollution. Don't do it. Just get back in and drive some more :_>

 

It also strikes me as being a huge waste of time. If you can fill the tank with 8 gallons in 90 seconds normally, but you can get in 9.5 gallons by filling at half speed, waiting, and then slowly adding more until it's topped off, you're not saving any time in the long run.

 

reality check, please....
1) has anyone experienced the gasoline spit-back from their Prius?
2) 90 seconds versus two minutes for a fill-up?!

1) i could get spit-back from several previous cars i've owned, and i can't imagine why the bladder in the Prius should make that any worse... you make it sound like it's getting over-stretched, then bouncing back... off what?, the inner wall of the metal tank?! the physics don't make sense. i'd blame a good old bubble in the filler neck for the problem, and i'd been filling my previous taurus up as much as i had patience for, to get "repeatable" mileage, for its whole life, and the engine ran like a clock and nothing indicated that the vapor recovery system or anything else was affected.
2) by the time you've gone even fifty feet off your normal driving route to fill up the car, and pulled back into traffic, you've completely washed out the extra minute you spent topping off the tank, rather than paying up just when the nozzle cuts off, so i don't buy that logic, either, sorry. getting caught up in optimal multi-tasking like that kills my fun of driving, and refueling is just part of the voyage.... otherwise, i end up wasting more than a few minutes figuring out how to wash the windshield AND buy a lotto ticket in the time it takes that bubble to go down.

relax and smell the roses!

ps... you just spent more time than that reading this message and the others before it, along with composing and typing your reply.
heck, you probably took longer to boot up your pc and open your browser!

 

No, I haven't experienced it, I'm too chicken to try to go past putting in more gas than I've driven.

I only know rflagg and one other (I can't remember now) - and both of them were doing the top-off method.

 

no beef, Doc... just didn't see the logic of how it could happen.

and, to be honest, i haven't refilled my tank yet.

it's puzzling that they'd put a tight rubber gasket in there to seal the filler tube, though... if there's no way out for any air in the bladder/tank, unless the bladder is very soft and collapses along with the fuel drained out of it, that spit-back is a problem begging to annoy or hurt someone!

:wave: (hope we can still be friends...)

 

So your point is that because I enjoy spending a few minutes reading a message board, I should waste time in all other aspects of my life too? Sorry, I'll pass.

I don't deviate even 50 feet from my route to get gas. There are a number of good stations that are right along the road.

> by the time you've gone even fifty feet off your normal driving route to fill up the car, and pulled back into traffic, you've completely washed out the extra minute you spent topping off the tank, rather than paying up just when the nozzle cuts off, so i don't buy that logic, either, sorry.

Logic just is. If you don't "buy" that 2+2=4, that doesn't make it false.

Time how long it takes you to get gas starting from the moment you enter the station to when you leave. With a normal fillup and with what others here have suggested (fill at half speed, wait a bit, then top off slowly). I guarantee you the second way takes almost twice as much time as the first way, if not more (assuming no waiting in line for pump, etc.). And this is all just to cut down the number of refueling stops by maybe 20%.

> getting caught up in optimal multi-tasking like that kills my fun of driving, and refueling is just part of the voyage

You're arguing IN FAVOR of standing around for an extra couple of minutes to get the maximum amount of gas in your tank. I said that it's better just to fill it up normally and drive away. You're being a bit hypocritical, don't you think? If you just want to refuel and get on with your fun driving, you should be supporting my point, not criticizing it. The ones trying to optimize are the ones sitting around at the pump. My point is that even so, they're losing time overall.

 

In regards to the "argument" here - re: filling completely up and taking a few extra minutes, or driving off when the pump clicks off - I think it's a "to each their own situation". For me, with my lengthy drive to work every day (close to 100 miles total a day), it makes sense for ME to put as much as possible in the tank, and take the few extra minutes if it gives me an extra day waiting time on filling up again.

However, someone who drives very little, or at the least, less than me - I could completely see their argument of filling to the click off point. To them, it's not worth it. To me it is. I think that should end that pointless argument.

I have found one thing that does seem to help relieve the pressure a bit, whether it's perceived or real, I'm not sure yet - but once you're past the click off point, put the nozzle in far enough so you'll be filling the tank, but keep it out far enough to have the nozzle 'holes' outside which will let a bit of air out while filling. Again, I'm not sure if I just perceived this to be a better method, or if it really works, but it's something I'll try again this coming weekend.

At any rate, I know with my filling techniques (especially now that I know what NOT to do after the spillover incident) can get me 500 miles a tank for this summer. If I went to the click off point, I'd lose 50-100+ miles a tank. Since my drive consists of 40 miles one way, I prefer this method.

The winter might be a completely different story, since we all know we'll be able to get less in with lower temps.

-m.

 

Hey, NOTHING ever ends a good pointless argument!

The bigger problem, for those concerned with emissions in addition to gas consumption, is that a single instance of backsplash over the next 5 years pretty much eliminates all the emissions benefits of the Prius. I was just trying to add a "time" argument to the mix.

Of course, on my way in this morning, I was behind a truck hauling asphalt. Made me depressed about how little impact my Prius was going to have as long as trucks spew large clouds of crap out into the air.

 

In my case, 'normally' has been to cram all the gas in I can for years now. My Kia was recalled to fix a filler tube blockage caused by (I believe) a pollution control device so that I didn't have to nurse the gas in ALL the time anymore, but all that did was make the initial fill faster THEN the nursing started. All my other cars were easy to fill, so I did.

Of course, back when I did a lot more than my current 20,000 miles per year of driving, I would often be driving at 3AM during a period when 24-hour gas stations weren't common on the roads I was using. Early 80's had me in tight spots occasionally sweating out those last few miles to an open station, so a habit of putting in all the gas I could developed, and I see no good reason to stop...

 

Just as another data point, my 04 Prius, built just last month, consistently accepts 9.5 to 10.5 gallons. I generally fill up within a few miles of the Add Fuel warning / blinking. Temps up here in the Pacific NW have been 48 to 80 deg. F.

Since this particular specimin of Prius does not seem to have a trouble with "shrunken bladder syndrome" I don't know how far past the warning I can drive, thus I fill up ASAP. I'm already on 480 miles on this 50 MPG tank, and the warning hasn't happened yet. I expect I'll have to re-fuel on the way home.

 

I think what the Prius needs is a 500-gallon fuel tank. Then we'd only have to gas up once every two years. (Your results may vary, depending on how many miles you drive per year, your ambient temperature, and your driving habits, as well as the SOC of your battery when you filled up.)

 

with a good vapor recovery system, you will have a fairly good seal on the mouth of the filler neck. in the Prius which IS NOT vented into the atmosphere, filling the car creates presurized air. the air will only compress so much until it will forcefully stretch the bladder. removing the filler nozzle releases the pressure resulting in the bladder shrinking back to its normal shape resulting in spillage of gasoline if there is insufficient space for the gas to expand into.

 

well, i'm going for the record of lowest mileage on a Prius... after about two months of ownership, i've finally gotten the fuel gauge down to the last button, and i decided to no wait for it to blink. so i refuelled yesterday on the way home from the car wash (bad idea... do it in the other order next time.... memo to self)

i got about 9 gallons in before the pump cut off the first time. then i slowly added about another gallon and a half. no spillage, no spit-back.

here's where i question what's going on here: the little rubber seal that the fuel nozzle goes through can't be a tight seal for the air from the tank to exit, or else you'd be pressurizing the tank by putting ANY fuel in, and the same volume of air would be puffed out back at you. so the seal can't be a tight one. air has to come out of the tank continually as you fill it, and pressure buildup just can't happen.

now, if the bladder sits inside a metal container (the "tank"), as you drain it by running the engine, either air must be let into the bladder or the bladder must shrink away from the outer metal tank. unless there is some way for air to get into the metal tank between the bladder and the tank, that bladder won't "collapse" or "shrink" at all! the difference in volume has to be refilled with something!

my bet is: the metal tank is vented, probably to the filler neck. the fuel going into the bladder can then expand the bladder until it fills up the metal tank (hits the walls and ceiling). only at that point does the fuel start to fill up the neck that goes from the little door on the side of the car to the bladder itself.

pump nozzles, as i understand them, have small holes which sense the fuel coming up to that level, and when the holes get covered with fuel, the pump nozzle cuts off. pulling the nozzle far enough out to get those holes outside of the rubber "plug" is inviting the fuel to overfill the tank's neck and come splashing out at you (or on you!).

but once the nozzle cuts off the first time, as long as you keep squeezing the handle, it will fill the neck of the tank up to the nozzle and cut off. that's how i got the extra gallon in. no other way.

and, btw, the fuel underground in the tank will, yes, probably be colder than the air above ground (and the car it's going into), and will expand after it gets into the tank.

only problem with this worry is: it'll heat up and expand pretty slowly, and by the time you've put the cap back on the tank and clicked it, the gas will not have expanded enough to push out of the tank! and after you've driven a while, the next bit of expansion will have been taken up by the ICE removing it and burning it!

finally, once you cap the system, it's a closed system, and it can't let fuel vapors escape. that's the law, right? so even if you filled the tank and moved the car immediately into the sun on a hot day, no fuel can get out.

i'm just trying to follow the evidence here, as they'd say on CSI, and i haven't seen any explanations that worry me about topping off the tank.