Gas Level Increased After Fill-up and Overflowed

[Twism86]

So here is a strange thing that happened last night, maybe someone has a better explanation:

I pulled into a gas station after a 170mi non-stop ride. I filled up to the bottom of the little neck that goes into the tank as i always do. I ride about 1mi home and put the bike on the side stand. Within a few minutes i noticed gas coming out of my overflow tube. I open the cap and the gas is at the top and going over and into the drain hole. I stand the bike up and give it a shake and the level goes down to the bottom of the collar as it fills some voids in the tank. I put it back on the side stand and watched the level increase until it was over flowing again. I did the same thing and it went down, then back up again. I finally had to siphon a glass full of gas out to get it to stabilize below the neck.

Any reason for this? Cold gas expanding once it went into a very hot bike? Fuel flowing back into the tank from the carbs/ fuel lines?

Tom

[The Buddha]

Yea gas vaporises and whatever.
Cool.
Buddha.

[Elijafir]

my best unscientific guess would be that that 'cold' fuel created a 'cold air pocket' above the 'neck line' and then the heat expanded the air/gas vapor and started pushing the fuel out of the tank.  I don't think fuel itself expands that much.

[jp]

my best unscientific guess would be that that 'cold' fuel created a 'cold air pocket' above the 'neck line' and then the heat expanded the air/gas vapor and started pushing the fuel out of the tank.  I don't think fuel itself expands that much.

This is the most likely case. The coefficient of thermal expansion for gasoline is 9.6e-4, and air is 3.7e-3. So the pocket of air in the gas tank will expand 3.85 times as much as an equal volume of gasoline. It will also absorb the heat faster than the gasoline.

[Gary856]

my best unscientific guess would be that that 'cold' fuel created a 'cold air pocket' above the 'neck line' and then the heat expanded the air/gas vapor and started pushing the fuel out of the tank.  I don't think fuel itself expands that much.

Brilliant!

This woudln't happen if, with the bike resting on the sidestand and thus tilted slightly, the gas was filled only up to the low side of the filler neck, which would allow the expanding air to escape from the high side of the filler neck.

[StevenDavisPhoto]

side question... sorry to hijack...

does the gas auto stop like on a car? or do u just have to fill it up manually. i've only put about 90 miles on my bike so far, so have yet to fill it up.

[zach93]

side question... sorry to hijack...

does the gas auto stop like on a car? or do u just have to fill it up manually. i've only put about 90 miles on my bike so far, so have yet to fill it up.

have to manually

[Twism86]

You mean like stops pumping when its full? It will but i dont recommend filling it with the nozzle that far into the tank. Just watch it, its easy...

[mister]

side question... sorry to hijack...

does the gas auto stop like on a car? or do u just have to fill it up manually. i've only put about 90 miles on my bike so far, so have yet to fill it up.

The auto stop is a function of the pump. If your nozzle is deep enough in the tank for it to be covered with gas and then autostop, you will not have filled up your tank.

Like Twism said, just watch it. As it gets close to the tank sleeve, slow down otherwise it'll splatter out a little. Once it gets to the bottom and starts to come up the sleeve, stop filling. You're full. Reset your trip meter, pay for your gas and ride off knowing you've got one of the most long range bikes around with one of the largest tanks.

Michael

[twocool]

I notice that after I stop after a ride, that the engine head migrates up into the gas tank...gets pretty hot!

I think the explaination of trapped air in the tank expanding is the deal here..........but gas alone can expand a lot too.

I work with airplanes.......if you fill the wing tanks in the morning, and it gets hot during the day, fuel will come out the overlow.............not due to trapped air, as the tanks are vented.....but due to expansion of the gas itself........

Airliners load up with fuel by the pound, not by the gallon, because if was a hot day, and they used gallons, they might not have enough fuel........the power in fuel is measured in power per weight(mass), rather than power by gallon.


Cookie

[chopobo]

Sorry to hijack this thread but this is sort of related.

When I fill up my gs500f I fill it all the way up to the neck then jiggle the tank and watch the petrol level go down and keep filling her up and jiggling the tank to fit in more fuel.

I can fit in an extra 0.5L to 0.75L I reckon from doing this.

(Though must look a bit silly jiggling a bike between my legs doing this)

Does anyone else practice this?

Is there any bad effect from doing this?

[the mole]

Twism, the GS is very economical, but yours is actually making gas. Keep draining out those cupfulls and you can sell it cheap to gstwinners!

[twocool]

Sorry to hijack this thread but this is sort of related.

When I fill up my gs500f I fill it all the way up to the neck then jiggle the tank and watch the petrol level go down and keep filling her up and jiggling the tank to fit in more fuel.

I can fit in an extra 0.5L to 0.75L I reckon from doing this.

(Though must look a bit silly jiggling a bike between my legs doing this)

Does anyone else practice this?

Is there any bad effect from doing this?

Well first of all it indicates that you have an obcessive, compulsive disorder......you ever watch TV show "Monk"?

What the heck are you trying to possibly acheive with that extra 1/2 litre?   Two extra miles?   Do you always run the tank dry between fill ups?  Is it that far between petrol stations that you MUST have that extra 1/2 litre?  Do you always ride for 5 hours straight without a stop?  

Really.......every owners manual I've seen says just fill up to the bottom of the filler neck, not over........

This allows the proper air above the tank and will let the vent work properly not will not cause overflow as in the above case.........

There was on report a a guy having the gas overflow in a turn, spill onto the rear tire, and cause a slip!

If you really need to be anal, obsessive, compulsive, just stop  every single time a bug  smashes on the windshield, and wipe it off!


Cookie

[Firewalker]

You mean like stops pumping when its full? It will but i dont recommend filling it with the nozzle that far into the tank. Just watch it, its easy...

Had to jump in here......the main problem area of rust in my tank is directly in line with where the gas nozzle would be if you just hung it in there to fill it up.  Probably several scrapes over time cause it to happen in this area.  I have always held onto it while fueling because as you say, it would click off after a gallon or so if you didn't.

[Twism86]

Twism, the GS is very economical, but yours is actually making gas. Keep draining out those cupfulls and you can sell it cheap to gstwinners!

Lol i knew someone would chime in with a reply like that.

[jp]

When I fill up my gs500f I fill it all the way up to the neck then jiggle the tank and watch the petrol level go down and keep filling her up and jiggling the tank to fit in more fuel.

I can fit in an extra 0.5L to 0.75L I reckon from doing this.

I do this when I fill up, but I don't squeeze in quite as much as you do. I do it mainly to fill to a consistant level, not because I need the extra range. If you stop as soon as you get to the bottom of the fill neck, you get a larger variation in how much gas goes in the tank each time. It isn't much by volume, but the largest source of error in tracking gas mileage is from measuring the amount of gas used. Since I track my gas mileage, my inner lab nerd forces me to take the extra time do fill the tank as consistantly as possible.

[twocool]

When I fill up my gs500f I fill it all the way up to the neck then jiggle the tank and watch the petrol level go down and keep filling her up and jiggling the tank to fit in more fuel.

I can fit in an extra 0.5L to 0.75L I reckon from doing this.

I do this when I fill up, but I don't squeeze in quite as much as you do. I do it mainly to fill to a consistant level, not because I need the extra range. If you stop as soon as you get to the bottom of the fill neck, you get a larger variation in how much gas goes in the tank each time. It isn't much by volume, but the largest source of error in tracking gas mileage is from measuring the amount of gas used. Since I track my gas mileage, my inner lab nerd forces me to take the extra time do fill the tank as consistantly as possible.

Yeah, it's good to have a definite "fill mark" for consistancy.........for me this is when the gas hits the filler neck, with the bike on the side stand......you could let it hit both sides of the neck, it sort of makes a bubble, but stop then so as not to overfill.

But as to the gas mileage deal...........if you keep a running average..........over lots of fill ups, that tiny difference in fill level becomes meaningless.........

Example:

You run 60 miles and fill up with 1 gallon = 60 MPG

You run another 60 miles but now when you fill up you "over fill" so it takes 1.1 gallons.........looks like 10 % difference in gas mileage..............or 54 MPG


Now run like 20 tankfulls..........like 100 gallons.........so you have 6000 miles on the clock...........you've kept track of all the gas that's gone in.............the only possible error is the difference from the first fill up, to the last fill up....

so now the error is down to 1/10 of 1 percent

so mpg looks like 59.94 instead of 60.  Big deal!

Ok maybe you want to check MPG over a certain course, or for certain weather, wind etc.....or a run when you "baby" the bike and one run "all out"..........

But the shorter the sample the bigger the possible error...

Cookie

[Elijafir]

I usually over fill to round up to the next dollar.. lol.   E.G. If I hit the bottom of the neck at $8.25 I will "over-fill" the next $0.75.  Just have to go real slow to keep from bubbling/splattering.  I have never had a problem with my fuel over flowing or spilling out.  I also always ride at least a mile after I fill up. Don't know how much that matters though. 
As far as the "auto-stop" function.. if you held the tip of the gas pump nozzle so it was right at the bottom of the filler neck it would work just fine.  You would probably get some splatter though.

[twocool]

I usually over fill to round up to the next dollar.. lol.   E.G. If I hit the bottom of the neck at $8.25 I will "over-fill" the next $0.75.  Just have to go real slow to keep from bubbling/splattering.  I have never had a problem with my fuel over flowing or spilling out.  I also always ride at least a mile after I fill up. Don't know how much that matters though. 
As far as the "auto-stop" function.. if you held the tip of the gas pump nozzle so it was right at the bottom of the filler neck it would work just fine.  You would probably get some splatter though.

In my country, we have something called "coins", often used for money............when the tank is full at $8.25 I give the guy $8 and a quarter!.........Or maybe $10 and he gives me a dollar and three quarters....try it....seems to have worked well for the last 200 years or so!

Actually, I have never put in over $7.00 to fill my tank....gas is $2.43 around here now.....My long commute is 160 miles and it takes exactly 2.4 gallons or  $6........

Cookie

[Elijafir]

I like to run on res for a while.. at $2.80+ / gallon (91 oct) i regularly put in 8 or 9 dollars.  Also, I usually pay at the pump w/ my debit card.. So, yeah it's totally an ocd habit from when i used to pay cash and didn't enjoy having pockets and ashtrays full of change all over the place.