Auto-shutoff not filling the fuel tank?

[Friggin Idiot]

Has anyone else noticed that the auto-shutoff on the gas pumps ends up not completely filling your tank? For the most part I had been filling the tank until the auto-shutoff and going along happily. That was until I realized that I wasn't driving as far as the first tank or two I'd put in the truck. I've been experimenting with it the past several times at the pump.

After the auto-shutoff, I can squeeze the handle to the slowest setting and still fill up more. Doing this I get a more into the tank before the auto-shutoff triggers again. And it's about 2 gallons more, not just an extra 2/10ths or some piddly little amount. This has been consistent across several different stations and pumps, so it's not isolated just to a faulty pump. The time of day or temperature don't change this. I see the extra miles between fill ups too. Has anyone else run across this in their 5th gen?

I'm thinking it's just the last of the air escaping from the top of the tank as it fills that last little bit. The speed of the air being displaced may be causing an early pressure differential and triggering the auto-shutoff. Then when I add more, slowly it doesn't trigger the shut-off until an actual pressure differential is reached. I get to fill up the last of that space, and the filler neck to get those extra 2 gallons. Yes I know this disobey's all instructions not to top off your tank, but when it's 2 gallons, that's an extra 35-40 miles.

 

[Ducmonsta]

I believe you can fill up and get the last two gallons in. You are definitely displacing the air in the tank for the last 2 gallons. The reasoning behind this is to account for the expansion of fuel when it warms up. Ever leave a plastic fuel can outside for just 10 mins in the heat of summer? It doesn't even have to be in direct sunlight. It turns into a globe of a fuel can. I wouldn't want to risk fuel overflow while driving just to get the extra 35-40 miles out of a tank. So far were in the winter season in most of the country. I'd like to hear about your experience in the middle of the summer.

 

[NoDak]

and filling up to the neck is also bad for the charcoal canister. too much fuel constantly being overflowed into it ruins it faster.

 

[1engineer]

Has anyone else noticed that the auto-shutoff on the gas pumps ends up not completely filling your tank? For the most part I had been filling the tank until the auto-shutoff and going along happily. That was until I realized that I wasn't driving as far as the first tank or two I'd put in the truck. I've been experimenting with it the past several times at the pump.

After the auto-shutoff, I can squeeze the handle to the slowest setting and still fill up more. Doing this I get a more into the tank before the auto-shutoff triggers again. And it's about 2 gallons more, not just an extra 2/10ths or some piddly little amount. This has been consistent across several different stations and pumps, so it's not isolated just to a faulty pump. It also makes no difference whether I'm parked uphill, downhill, or sideways. The time of day or temperature don't change this either. I see the extra miles between fill ups too. Has anyone else run across this in their 5th gen?

I'm thinking it's just the last of the air escaping from the top of the tank as it fills that last little bit. The speed of the air being displaced may be causing an early pressure differential and triggering the auto-shutoff. Then when I add more, slowly it doesn't trigger the shut-off until an actual pressure differential is reached. I get to fill up the last of that space, and the filler neck to get those extra 2 gallons. Yes I know this disobey's all instructions not to top off your tank, but when it's 2 gallons, that's an extra 35-40 miles.

Two things:
1. You can drive 5-6 hours before you have to stop to fill up? You can go that long without peeing or stretching?
2. You drive until your tank is down to two gallons?

 

[oljedi11950]

Two things:
1. You can drive 5-6 hours before you have to stop to fill up? You can go that long without peeing or stretching?
2. You drive until your tank is down to two gallons?

HAD to mention about the peeing huh ? When mine clicks off i just round it to the dollar & roll . :dammit:

 

[NoDak]

Two things:
1. You can drive 5-6 hours before you have to stop to fill up? You can go that long without peeing or stretching?
2. You drive until your tank is down to two gallons?

I use to do that, but then I got a warden and rug rats. im lucky I can 110 miles before one of them is saying pull over somewhere. hell from minot to Bismarck (capital) its 106 miles, rarely do I make it the 106 miles without stopping that someone is saying pee time

 

[Friggin Idiot]

I wasn't so concerned about expansion, how much can it really be right? So I tried to think like [MENTION=66316]1engineer[/MENTION]:

I went and found an answer. Gasoline expands at a rate of .000950 per degree C. Now it's a typical Okie spring here with ~50 degree F temp swings between night and day. But I'm going to use a worse case scenario of someone out in the AZ desert of 120F (49C) in the daytime desert, and 32F (0C) in the driveway at night. Likely? probably not, but why not exaggerate a little to give a margin of error?
So that's .000950 x 49 = .04655 change in just one gallon, not much.
The 5th Gen 4Runner has a 23 gallon tank I think? So that means what reads brimming topped off max just after sunrise (coldest time of day) will overflow 1.07065 gallons once heated to max ambient air temp if the level is unchanged after filling up.

Let's think a minute, fuel tanks are buried, and kept warmer/cooler by the surrounding earth. So you're not really pumping 0C fuel into your tank, you're probably pumping 4C fuel that would have to be cooled to ambient air temps first. 23 x .000950 x 4 = .0874 gallons of shrinkage assuming you get it with the heat blowing back from the engine, warmer passenger compartment above, and pavement temperature. Assume worst case, no shrinkage (shrinkage is never good right? LOL!).

FWIW I also don't think you could actually get the fuel tank up to 120F (49C) unless it was painted black, and you have your tires pointed at the sun all day. If that's the case, you have bigger concerns than a gallon of gas! So let's say that fuel reaches a more modest but still toasty 37C (~99F). Now the change in temp is only 33C. 33 x .000950 x 23 = 0.72105 gallons of expansion.

Now most of us 4Runner drivers probably don't live out on the farm with our own fuel pumps, so we burn some gas getting the truck to where we need to be before parking it. How far from pump to parking is a variable thing. If I fill up on the way home, I have a whopping 3.2 miles to the house, and mostly 60mph highway at that. If I fill up on the way to work that's ~19 miles, in which I'd burn off that gallon of expansion before it can even expand. So the problem is driving home after my overnight shift, filling up grabbing a donut (donut shop right next to gas station), and then going home to bed and parking the truck in the sun. So even with a Prius level .125 gallons consumed getting home leaves us with around .592 gallons of overflow (22.875 x .000950 x 33).

Remember this is all still worst case scenario.
I never fill up or get donuts after my overnight shift on the way home, and even if I did, I'm too tired to care about 2 extra gallons. My 4Runner goes in the garage, so there's no way there's a 33C (~60F) temp change from fill up in morning to heat of day (even accounting for radiant heat from cooling engine). Remember I don't live in the AZ desert, so my change in temp is much more likely 20F(11C) between fuel temperature at filling, and high at storage in the garage. This equates to about .25 gal expansion less the .125 gallon burn to get home, so just 1/8 gal overflow? Depending on how large the diameter of line, and how long it is to the charcoal filter, it might not even reach the filter. If the canister is mounted directly to the top of tank vent, then I might have an issue, although I don't even think this is likely.

So this sounds like I shouldn't be worried about my filter unless I'm constantly filling up at cold mornings right before parking in hot temperatures.

 

[oljedi11950]

Wow yes you did !!

 

[Friggin Idiot]

Two things:
1. You can drive 5-6 hours before you have to stop to fill up? You can go that long without peeing or stretching?
2. You drive until your tank is down to two gallons?

1. That's what empty Gatorade bottles are for. I'm single and don't care who wants to try and look while I'm doing 60+ on the interstate!
2. Never while on a road trip, only when local to home. Tank took 21 gallons including the extra 2, this afternoon at fill up on the way into work.

C. Those 2 extra gallons can mean the difference between an extra day commute to/from work.

 

[Ezlife45]

Ever watch gas going into a 5 gallon or 2 gallon can? It has a little bit of foam or bubbles that dissipate after a few seconds. That is part of what is shutting off the nozzles.

Next time when you think you are close to full, slow down your fill rate and you will get more fuel in there even without topping off.

 

[oljedi11950]

1. That's what empty Gatorade bottles are for. I'm single and don't care who wants to try and look while I'm doing 60+ on the interstate!
2. Never while on a road trip, only when local to home. Tank took 21 gallons including the extra 2, this afternoon at fill up on the way into work.

C. Those 2 extra gallons can mean the difference between an extra day commute to/from work.

:car::bolt::crazy: Qt size bottles I hope

 

[1000MPH]

Who pees at a gas station? That's gross.

Don't Top Off Your Gas Tank! | Mid-Atlantic Air Protection

 

[Friggin Idiot]

Don't Top Off Your Gas Tank! | Mid-Atlantic Air Protection

Yeap that sounds like the government, telling you what you should and should not do without ever explaining the reason or how things work. Just don't do this, especially when it affects a system THEY mandated be installed!

What was ever wrong with a simple overflow container like they have for the coolant. Just put a spring loaded plunger against the gas cap to close the valve between the main tank and the overflow when the gas cap isn't in place. Tightening the gas cap compresses the spring and opens the valve. The only drawback is that the overflow tank has to be able to withstand the pressure of a full main tank expanding in the heat against the volume of air in the overflow tank also expanding in the heat. That shouldn't be more than a few PSI right?

Even a ridiculous 40 gallon tank would only require a 1.75 gallon overflow tank (1.52 gal actual expansion) for a 40C (72F) temperature change. Too worried about air quality instead of how to keep things simple. Simple doesn't break as easily as all those complicated solenoids and vacuum systems. Remember vacuum systems rob power from the engine too! Hell this simple system requires no computer sensors. Because the only way to get air into the system is through the cap and filling neck, you would only need a cap that would act as a one way valve, allowing air into the system upon reaching a negative PSI (to compensate for fuel burned). If you set the check valve high enough, say -5 PSI, the system should even hold pressure after the fuel pump stops drawing at engine cut off. That low of a PSI should also keep fumes from escaping when removing the gas cap. At least long enough until the fuel nozzle with a built in vapor recovery system is inserted.

By default a fuel cap is usually covered for aesthetic reasons, meaning it is protected from the elements by default. They're also mounted high enough on the side of the vehicle for convenience that even most of us here would have trouble submerging them. I guess the EPA is what happens when a bunch of scientists and engineers are assigned to fix a problem which could easily be solved by a mechanic!

Damn, yinz just made me waste one of my million dollar ideas for the year!

 

[Saker]

I usually fill up at the fastest flow rate, when close to full, slow the fill rate down to minimize foam/bubbles, let it shut off automatically, fill to the next tenth of a dollar and call it full.
I've had to replace a charcoal canister from "topping off" before.
To me, that's something I can avoid by following my above practice.

just sayin'

 

[Sunriser]

I wasn't so concerned about expansion, how much can it really be right? So I tried to think like [MENTION=66316]1engineer[/MENTION]:

I went and found an answer. Gasoline expands at a rate of .000950 per degree C. {snip}

Thanks for this. You provide a plausible answer for one of those nagging questions that kept puzzling me - why I am never able to add more than 20 gallons in the tank - even when filling from bone dry empty.

It's a bit disingenuous from Toyota though - calling it a 23 gallon tank when only about 20 are usable - although I suspect all the manufacturers do the same.

The takeaway here is that the tank is never completely full. Which is a safer place to operate from than assuming you have a couple of gallons below the empty line on the gauge.

 

[ToyotaDoodz]

All above arguments aside, I've found that my tank fills more completely when the nose of the vehicle is lower than the rear. Therefore on road trips and faced with an inclined drive at the pump, I'll pull in with the nose downhill. My '03 4runner was the same way. It's not much difference but when you're driving 15+ hours to your destination, it helps in the long run. In town, it's no biggie. I stop filling at the second shutoff after a 20 second wait after the first shutoff.

 

[nglayton]

Don't Top Off Your Gas Tank! | Mid-Atlantic Air Protection

Sadly Oregon made this into a law, so once it clicks off you are done. No top offs, ever at any station. No self serve either.......

The attendants all freak out if you try and do it yourself. They won't even run it again for the second click off, it's a pain.

Occasionally depending on the station you can still get a second click off in, if the attendant is someplace else.

 

[nglayton]

Aux tank for 5th Gens??

As a side question........has anyone found a good source for an auxiliary gas tank for the 5th gens? Or even and over size tank that could replace the stock tank?

Yes, I know CBI can custom build one if they have your runner for a week or so......

 

[TheWraith]

Has anyone else noticed that the auto-shutoff on the gas pumps ends up not completely filling your tank? For the most part I had been filling the tank until the auto-shutoff and going along happily. That was until I realized that I wasn't driving as far as the first tank or two I'd put in the truck. I've been experimenting with it the past several times at the pump.

After the auto-shutoff, I can squeeze the handle to the slowest setting and still fill up more. Doing this I get a more into the tank before the auto-shutoff triggers again. And it's about 2 gallons more, not just an extra 2/10ths or some piddly little amount. This has been consistent across several different stations and pumps, so it's not isolated just to a faulty pump. It also makes no difference whether I'm parked uphill, downhill, or sideways. The time of day or temperature don't change this either. I see the extra miles between fill ups too. Has anyone else run across this in their 5th gen?

I'm thinking it's just the last of the air escaping from the top of the tank as it fills that last little bit. The speed of the air being displaced may be causing an early pressure differential and triggering the auto-shutoff. Then when I add more, slowly it doesn't trigger the shut-off until an actual pressure differential is reached. I get to fill up the last of that space, and the filler neck to get those extra 2 gallons. Yes I know this disobey's all instructions not to top off your tank, but when it's 2 gallons, that's an extra 35-40 miles.

I always top off my tank ...

Toyota rates our tanks @ 23 gallons and I've ran it till the fuel light comes on and ran it another 40miles more. At the auto shut off its barely 20gallons.

the most Ive filled was about 21.5gallons topped off

 

[Friggin Idiot]

Revisit. In the past week my 4Runner has gone a little more than 2600 miles. Since it's June the temperatures have been warmer and I've had plenty of opportunity to refill the tank testing for results.

I'm still able to get 1.7+ gallons into the tank after shut off, even at 95F ambient air temperature. This is only possible when the truck is parked on an incline with the front end lower than the rear. If the truck is level, or parked front end high, I can barely add anything to the tank after shut-off.