patin22

During the summer months here in Las Vegas we had temps of up to 116. After driving around on those really hot days I would hear bubbling deep in my gas tank and the fumes were *really* bad. I could hear the bubbling both with the cap on and off.

My mechanic couldn't figure it out and I have no idea what it could be. It still happens on occasion with the fuel tank at various levels. Any ideas what this might be?

It's an 02 4runner - 4wd, 81,000 miles.

stormin94

I dunno, maybe your vent is clogged, or something. I don't know if cars have fuel tank vents, but boats do, and mine was plugged, and it made a gurgling noise.

hopper

I from Vegas also. I dont think I have ever had that problem.

Offtopic...do you wheel your 4runner?

Nismo Convert

If that was the case, that would increase the boiling temp.

patin22

that sounds feasible....
Where might something like that be on a car?

It will continue for about 10-15 minutes after I turn the vehicle off.

I can also feel venting while it's going on. I can't tell if it's sucking or blowing but it seems to be the latter.

patin22

I've never heard of/had this problem myself until this summer. Those temps aren't always necessary though because it's been happening again recently. (not as bad though)

I do a fair amount of off-roading - quite a few great trails in the area.

mt_goat

Maybe the fuel in the return line. You don't happen to have headers do you?

stormin94

I'm not sure. I would guess that it would be somewhere near the fill neck of the gas tank, or maybe near the fuel pump. When I fill up my 4Runner with gas, When I take off the gas cap, there is usually a hiss of pressure that bleeds off when I open the cap. I don't know what that has to do with anything, but it might help you out a little, I guess.

BajaRunner

I would assume that the gas tank would have some sort of pressure regulator. The higher temperature = higher pressure.

What someone said above about a higher pressure would be increasing the boiling point, I don't think that is correct. A higher pressure shouldn't have an influence on that. Just think of a pressure cooker. Its still boiling in there, yet there is a higher pressure to get a higher temperature (because of the steam).

Also, I never heard of gasoline boiling. But, since it readily turns into gas, I don't think it would be that hard to do. The engineers would have taken this into consideration.

I would suspect something is clogged or the sounds you are hearing could be the movement of the gas tank due to a high pressure. This is just all speculation though.

patin22

No headers - stock besides a cold air intake and exhaust.

patin22

Thanks for the input guys.

I never get the hiss anymore when I take the gas cap off. I'm going to search the fuel system for a pressure release valve this weekend.

It's hard to find a consistent factor that makes it happen. Heat, of course but it also happens at random times. The fume build up in my garage gets really bad.
The truck runs fine and the gas mileage is about the same. I can't figure it out...

slus

Your pressure release system aka fart box should be up under your hood, drivers side. Mine lets out a blast every few seconds on a really really hot day.

fillsrunner4

I would bet its a clog in the vapor line that runs to the evap and charcoal canister
check out this site its got info for the 2003 tacoma but it should be real close to the 4runners system. look under the fuel section
http://www.deserted1.com/FSM/
http://www.deserted1.com/FSM/Repair_.../ftal/comp.pdf
hope this helps some.

I wonder if it might be a good idea to invest in a fuel line cooler? ive never really heard of boiling fuel but im no scientist and i dont remember doing anything like testing that in school

mt_goat

I have seen gasoline boil before. I once had a 5 gal steel military style gas can setting too close to a generator I was running. The generator ran out of fuel and as I opened the hot gas can a lot of pressure started venting and the can sides bulged as the gas started to boil, then the pressure in the can increased enough to stop the boiling. Then the venting released enough pressure it started boiling again, this cycle repeated 5 or 6 times as I was running away. I think that was one of my 9 lives used up.

My guess is your fuel is going through the fuel pump and high-pressure fuel line to your regulator on top of the engine where along the way it is picking up a lot of heat from an engine that is borderline overheating but your temp gauge doesn't show it because... well Toyota doesn't want you to worry about your coolant temp until it reaches about 240 F, where at that point the temp gauge starts to move from the center of the normal range...then the fuel that isn't needed for the fuel rail is returned to the fuel tank by the low pressure fuel return line. It is my guess that along this low pressure line trip back to the fuel tank that would be the most likely place for the gas to boil, especially after shuting down the cooling system and heatsoak has a chance to bake those fuel lines sitting on top of the engine. As the gas boils the pressure would just be released into the gas tank via the return line kind of like a kid blowing bubbles into a drink through a straw.

4biker

No, the reason a pressure cooker gets hotter is because the pressure raises the boiling point. Water boils at a relatively low temp, so by restricting the amount of gas the water can produce (by increasing the pressure), the water can contain more energy (heat) before boiling, thus raising the boiling point of water. Remember, water boils at a lower temp at high altitudes due to lower atmospheric pressure.
It's all about PV=nRT. If everything else is remains constant, the equation becomes P=T (except the squiggly equals sign that means "relative to," or in other words the pressure is relatively proportional to temperature) If the pressure increases, the temp increases. mt_goat's pucker-factor experience shows that with the hot gasoline, reducing the temp allowed the liquid to boil at temp it was currently at just by reducing the pressure in the tank. Yikes! - that's why normal gas cans have vents.

isaac338

fuel boiling is a real problem on some things. i remember a few years ago Ricky Carmichael's mechanics had to add a heat shield between his header and carb cause the fuel in the bowl was boiling and causing all sorts of weird stumbling and hesitation issues.

infiltrator

good to hear you have a cold air intake...

well, vegas aint too far from here.. it got about 115 for about 2 weeks... i was dying!!!

but i didnt have a cold air intake, or air conditioning!!!
i felt with that heat, the 4runner wasnt responding well AT ALL! i hated driving it in that temperature.

maybe its happened to me, but i dont know, i just get in and get out quickly, no time to do anything when its that hot outside...

you know what we need? heat days off work!

mt_goat

Exactly, looks like someone above has spent too much time riding waves at Pacific Beach and not enough time at Mesa College.

Dare44

u said u have exhaust my friends f150 was boiling its fuel because the exhaust was pointed at it, i would guess u did it right tho and didnt just cut it off

BajaRunner

... Hey I took my thermodynamics course last year and got an A!!! I know the ideal gas law forwards, backwards, thermal energy, heat, adiabats, isotherms, isochors, blah blah blah...

But, uhh. Its not the LIQUID water that is increasing in temperature, it is the steam. With your analogy, you can say with an extremely large pressure, water would not turn to steam at 400*C? Maybe I am just misinterpreting your point.

I know that a higher pressure will equate to a higher temperature, I just don't think that the boiling point (at which an element or compound like water) would be changed because of that. A pressure cooker uses the pressure of the steam and not the water.