Total Motorcycle Community Forums

I ride a vulcan 750 and recently had its 9000 mile maintenance work done. On my next ride, I went about 70 miles and when I stopped and turned the bike off, I noticed a hissing sound from the gas cap. I loosened the cap to release the pressure and then tightened it again. After about one minute the hissing sound started again. I opened the cap and the hissing stopped, so I left it open for a few minutes. When I returned about 15 minutes later, I heard gurgling coming from the tank and when I looked insde, the gas was bubbling just like when water boils in a pot. I have never had this happen before, but I've never looked in the tank when I returned from a trip before. I have never heard this before when I have stopped to fill up during a ride.
Does gasoline boil?
Is the situation I've described dangerous?
Logically, it seems to me that you shouldn't ride around sitting on top of a tank of boiling gasoline.
I asked the service manager at the Kawasaki dealership and all he could tell me was to leave the gas cap tight and let it hiss. He said that the gas cap had a vent to allow the pressure to release. He could not answer my question as to why the gas was bubbling and gurgling like it was boiling.
Does anyone out there have any experience or knowledge with situations like this?

can gasoline boil? yes. it's a liquid.

can it boil in your tank? I don't see why not if the tank gets hot enough (heat coming off the engine, sun beating down on it, etc....)

Leave the cap on and let the vent do its job.

Dangerous? Not unless you pop the cap off and hold a lighter over the fill nozzle.

If I remember correctly, gasoline is resistant to exploding, so unless your give it an ignition source, it won't go off (Knocking is a whole other story). So I wouldn't worry too much about it being a fire hazard, but if Murphy's law should apply, remember to Stop, Drop, and Roll

I remember clearing some land I had in West Virginia for my cabin and all I had was a 14 cheap chain saw........

Yea, gasoline boils like chicken soup!!!! that little chainsaw was boiling like crazy......I added more gas and kept cutting.....

Of course I was younger and dumber then......


Don't recall it ever doing it in a motorcycle though?

dan

Gasoline boils. The gasoline in your tank is not boiling. It is absorbing heat and expanding. It is also vaporizing and heat helps this along. The hissing noise is the vent on your tank or cap letting that pressure escape looooong before it gets anywhere near high enough pressure to explode. You can open the cap and release all the pressure present at that time at once, or you can leave it and let the vent to it's job, whatever you prefer. Just take the smoke out of your mouth before you bend over to loosen the cap.

As the tank and fuel cool, or you ride the bike and draw fuel out of the tank, that same vent will allow air back into the tank to prevent vacuum building and starving the engine of fuel.

BuzZz wrote:Gasoline boils. The gasoline in your tank is not boiling. It is absorbing heat and expanding. It is also vaporizing and heat helps this along. The hissing noise is the vent on your tank or cap letting that pressure escape looooong before it gets anywhere near high enough pressure to explode. You can open the cap and release all the pressure present at that time at once, or you can leave it and let the vent to it's job, whatever you prefer. Just take the smoke out of your mouth before you bend over to loosen the cap.

But he said the fuel was visibly bubbling, like boiling water.

does gasoline boil? sure! and when it gets boilin' enough you get this nifty little condition known as vaporlock

jonnythan wrote:

But he said the fuel was visibly bubbling, like boiling water.

So he did, my bad. But I still am not convinced it was boiling, at least from temp. It could have been bubbling from the sudden pressure release of opening the cap... technically boiling, I guess, but at a lower temp, or it could be vapor lock in the fuel line backfeeding as the tank is opened or something similar. Or it indeed could be boiling due to temp on a hot day with alot of heat kicking off the cylinders into the tank bottom. The tank is designed to take care of all of this with the vent system, so doing nothing is the best remedy. A cool down phase and parking in the shade with some air circulation couldn't hurt either....

I don't think gas can boil when it's used as fuel on your bike. There are certain mechanisms that prevent this from happening although nothing is fool proof.

http://www.engineeringtoolbox.com/fuels ... d_936.html

100-400 deg's looks like