Gas flowing up and out of filler hole after fill up? - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
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post #1 of 19 (permalink) Old 06-10-2019, 11:15 AM Thread Starter
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Question Gas flowing up and out of filler hole after fill up?

I had a strange issue with fuel overflowing out of my tank yesterday.

I went on a a couple hour ride with my GF. The bike ran great. It was 32 degress celcius. When I stopped for gas, I filled it up to the usual spot, which is right when it hits the splash guard (dunno what it's called) at the bottom of the filler's neck. Sometime I squeeze and extra bit in until that splash guard is 'just' covered. You know, to maximize my range. :P

Then I parked it while my GF went inside to use the bathroom. While I was standing there in the hot sun baking, I noticed I could smell gas and when I looked over at my bike, I could see fuel flowing out from under the gas cap and down the side of my tank into the engine area. I quickly took the gas cap off to see if it was a venting issue and would stop, but it didn't, it just kept (over)flowing up and out. I ended up using a spare rag I had on hand to sponge a decent amount of fuel out so it would stop flowing out and running down all over my bike. That worked, but afterward, I could still see what looked to be air bubbles pushing the fuel up and trying to get out. Luckily, I had sponged out enough fuel that it was no longer bubbling up high enough to overflow out.

I waited until we were ready to leave before putting the gas cap back on, and it was incedent free for the 2 hr ride back home.

Any idea what caused this? Excessive heat combined with filling it up too high?

Here's a pic from the Ride

Current Bike:
2008 Yamaha V-Star 1100 Classic

Previous Bikes:
2005 Yamaha YZF-R6T
1990 Kawasaki EX-500

Last edited by CanadianMohawk; 06-10-2019 at 11:18 AM.
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post #2 of 19 (permalink) Old 06-10-2019, 11:39 AM
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Google says:
Gasoline or petrol is a fuel, derived from petroleum crude oil, for use in spark-ignited internal combustion engines. It has an initial boiling point at atmospheric pressure of about 35 C (95 F)

With the gas tank sitting on top of a hot engine, in the sun, you were experiencing the fuel boiling. You were already at 32 degrees C ambiant temperature. It's common in Texas, I never fill my gas tank all the way full because of this. In some situations you will get vapor lock, (vapor from boiling gas enters fuel line) and creates a none fuel flow issue.
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post #3 of 19 (permalink) Old 06-10-2019, 11:42 AM Thread Starter
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Quote:
Originally Posted by lesblank View Post
Google says:
Gasoline or petrol is a fuel, derived from petroleum crude oil, for use in spark-ignited internal combustion engines. It has an initial boiling point at atmospheric pressure of about 35 C (95 F)

With the gas tank sitting on top of a hot engine, in the sun, you were experiencing the fuel boiling. You were already at 32 degrees C ambiant temperature. It's common in Texas, I never fill my gas tank all the way full because of this. In some situations you will get vapor lock, (vapor from boiling gas enters fuel line) and creates a none fuel flow issue.
Interesting. That makes sense.

I've never experienced this on my previous bikes (one was carbed, one was fuel injected). The fuel also did'nt feel hot at all when I sponged it out with a rag. In fact, it felt cool to the touch?

Edit: Maybe it felt cool because i was touching the fresh fuel at the top of the tank but it was the existing fuel that was boiling while mixing and forcing the fresh cool gas up and out?

Current Bike:
2008 Yamaha V-Star 1100 Classic

Previous Bikes:
2005 Yamaha YZF-R6T
1990 Kawasaki EX-500

Last edited by CanadianMohawk; 06-10-2019 at 11:45 AM.
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post #4 of 19 (permalink) Old 06-10-2019, 11:58 AM
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I think its more of a case that you filled the tank all the way, nearly to the brim, with gas from a tank in the ground

the gas coming out of the hose could have been very cold, maybe 5C

when you filled the tank with the engine hot, and sitting in the hot sun, the gas quickly warmed up and expanded, forcing it out of the cap

I was not aware that gasoline "boils" from 100F to 400F - the definition of boiling is when the fuel vapor = 1 atmosphere in an "open" container.

If the container is sealed the pressure will increase as the temp increases, raising the boiling point.

I guess it could be a little of both.

I never fill the tank all the way to the brim unless Im riding and know I will be going at least another 20 or 30 miles to pull the tank down a few quarts, before I stop.
Now that I typed that out loud, that is not good either, because I might intend to get on the bike and ride another 30 miles, but who knows, something might happen a mile down the road causing me to stop... I guess I should stop doing that.

Filling the tank all the way, and then parking the bike for the day is the worse case situation.
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post #5 of 19 (permalink) Old 06-10-2019, 12:01 PM
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Wow. I've heard of and seen fuel dripping out of the vent hose before but not coming out from under the fuel cap. Which make me wonder if your vent-system is working. This almost sounds like a demonic possession!

Eastern Washington state is very similar to Texas. I've also filled mine up and then it sat in the sun while I exercised my butt muscles in much needed walk/stretch periods. Not once did it so much as hiccup in 90+ degree weather. How much is 32 degrees C in real temperature (F)?

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post #6 of 19 (permalink) Old 06-10-2019, 12:02 PM
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thinking about this some more, if you fill the tank up to the bottom of that tube on the fill inlet, and if the tank vents thru the gas cap

then when you stand the bike up, if the fuel completely covers the bottom of that filler tube, even if there is air in the top of the tank, as the air and gas heats up, and the pressure vents out the cap, then the gas will be pushed up that tube quickly and out the gas cap, if the pressure has no where else to go.

is there suppose to be a vent tube somewhere else on the tank, at the highest point?

I have to look at the tank drawings now....
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post #7 of 19 (permalink) Old 06-10-2019, 12:10 PM
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looked at the exploded tank drawings on bikebandit - Ive had the tank off my 650 and Royal Star, there are no tank vent tubes that Im aware of - so the tank must vent thru the cap

so yes, unless that short tube that extends down from the filler port has an inside opening near the top, it would tend to push the fuel up out of the cap when the entire lower end of the tube is completely immersed in the fuel in the tank....

I have been getting away will filling my tank all the way to the brim for several years now.
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post #8 of 19 (permalink) Old 06-10-2019, 12:12 PM
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Google says:
Gasoline does expand and contract a little depending on its temperature. When gasoline rises from 60 to 75 degrees F, for instance, it increases in volume by 1 percent while the energy content remains the same.

2001 Vstar 1100 Classic (sold), Cobra Slash Cut full exhaust, Dropped 1 inch with lowering links, ORK, 4.5 inch handlebar risers, Ultimate passenger seat, Passenger pegs moved forward 4 inches, Handlebar clock, KN air filter, Viking saddlebags, Additional rear lighting
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post #9 of 19 (permalink) Old 06-10-2019, 12:17 PM Thread Starter
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Quote:
Originally Posted by 750 Chris View Post
How much is 32 degrees C in real temperature (F)?
LOL. We are metric up here but some old schooler's still use F.

I too suspected venting, but the only way in and out of that tank is the petcock or the gas cap. I know because I've had it off several times and even had to clean rust out of it. When i removed the gas cap, it kept on overflowing so that doesn't seem to be the issue. The petcock is brand new.

I've also been filling like this since I've had the bike, which admittedly isn't that long. I've only put about 2500kms on it since I got it. However, considering I have to fill at just under 200kms, that's a lot of fills and never had this issue before.

It has to be heat related though. I decided that going forward, I better be ready to immediately ride some distance if a) It's hot outside and b) I continue to fill it right to the rim like I have been.

Otherwise, I'm at a loss. Also, i never really thought about the fact that it's sitting on it's side when I'm filling it to the brim. Then when I stand it up...hrm...fuel must be touching the gas cap at that point. Not a huge issue since I usually then pull out and put some kilometers on it bringing the level down. However, in this situation, I just moved it to a parking spot and it was still on it's side stand when it started puking gas out.

Current Bike:
2008 Yamaha V-Star 1100 Classic

Previous Bikes:
2005 Yamaha YZF-R6T
1990 Kawasaki EX-500
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post #10 of 19 (permalink) Old 06-10-2019, 12:21 PM Thread Starter
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Quote:
Originally Posted by lesblank View Post
Google says:
Gasoline does expand and contract a little depending on its temperature. When gasoline rises from 60 to 75 degrees F, for instance, it increases in volume by 1 percent while the energy content remains the same.

It has to be this Les. Hot day, hot bike, cool gas combined with filling it up as far as I could...and it was a station in the middle of nowhere thus, questionable quality fuel. Expanding gas seems a more plausible explanation to me than boiling gas.
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Current Bike:
2008 Yamaha V-Star 1100 Classic

Previous Bikes:
2005 Yamaha YZF-R6T
1990 Kawasaki EX-500
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