Gas boiling in tank

[dreksnot]

Got an interesting phenomenon going happening. After a 15 minute or so drive and pull back in the garage, shut off the car, I can hear what sounds like boiling coming from my fuel tank. It's noisy at first then slowly fades away over 10 minutes, getting quieter as time goes by (as things cool down). It really sounds like my 91 octane is boiling (I've attached a .mpg file that's been zipped in order to attach here). First I thought it was because I was running 2 fuel pumps all the time (at 58psi). So, I shifted back to 1 fuel pump (trying one then the other pump to see if it was a singular pump issue) and also lowered the FP to 43.5psi thinking that would create less heat. No bueno. Appears the same. I've hit my fuel rails, regulator and fittings under the hood with my pyrometer and they're toasty at around 135F. My exhaust is not close the the fuel tank. My 9" differential pyro'd 130F. Barometric around here is 12.2psi. So, does anyone have any idea what can be going on?

[larry_g]

Something with the venting?



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[dreksnot]

Originally Posted by larry_g

Something with the venting?

My evap system is removed

[G8One2]

So your EVAP and tank is completely sealed?

[Batmanntexas]

I would expect the components under the hood to be toasty, as the engine bay itself will be toasty. It can only be a few things causing your issue, I'd think, so here are my guesses:

1. Fuel line shifted close to the exhaust (which you ruled out)
2. really small fuel tank and your seriously cycling the fuel through the system (not likely)
3. Pumps are drawing excessive current causing them to impart more heat into the fuel system.

Do tell what you find, though.

Good luck,
Scott

[fz4k98]

It may be pressure releasing back into the tank from the fuel line. You could try safely cracking a fuel line open right away to see if it stops.

[eLeSthree]

Be interested to see what the temperature of your fuel hat is. Do u have a trap door?

[dreksnot]

I got a chance to jack up the rear after a spin around town. I heard gurgling from both sides of the fuel tank, more like the front of the tank. The pumps are only on the passenger side. I'd heard noise from one side then immediately the other side. Interesting... My evap system was removed years ago. Starting to think it's some kind of air noises and not boiling in the tank - but my differential pyro'd 175F and it's pretty darn close to the head shielding, which is pretty darn close to the fuel tank.

[TuneAFish]

I don't think 175F is enough to cause actual boiling (I am presuming fuel would boil at the same temp as water?).

If you crack the gas cap immediately after returning home, does it stop?

If there is air in the lines and (perhaps) the return line is slightly plugged, you might try turning the ignition back on right after shutting it off to allow the pump(s) to kick back on and see if that stops it. That would also support the theory that it's air in the lines somewhere.

The first actual 'change' I'd make is replace the fuel filter. It doesn't seem logical that it would cause this if it was plugged, but something is surely going on.

If none of those helped, I'd contact the pump manufacturer to see if there is some weird baffling/pressure equalizing setup between those pumps that might be trying to equalize pressure. I doubt that is it, but I'm also fresh out of other ideas.

Good luck!

[dreksnot]

Originally Posted by TuneAFish

I don't think 175F is enough to cause actual boiling (I am presuming fuel would boil at the same temp as water?).

If you crack the gas cap immediately after returning home, does it stop?

If there is air in the lines and (perhaps) the return line is slightly plugged, you might try turning the ignition back on right after shutting it off to allow the pump(s) to kick back on and see if that stops it. That would also support the theory that it's air in the lines somewhere.

The first actual 'change' I'd make is replace the fuel filter. It doesn't seem logical that it would cause this if it was plugged, but something is surely going on.

If none of those helped, I'd contact the pump manufacturer to see if there is some weird baffling/pressure equalizing setup between those pumps that might be trying to equalize pressure. I doubt that is it, but I'm also fresh out of other ideas.

Good luck!

I appreciate your suggestions. Gasoline is a funny liquid with no specific boiling point, like 130-400F depending on a lot of things like additives, atmosphere, etc.

Cracking the gas cap has no effect, nor can I hear the gurgling through the gas cap area (must be the check flow valve in it).

I'll try the cycle the pump after engine shutoff to see if there's any effect.

I have the fancy ID fuel filter and the integrated Diff Press gauge says the filter is clean and fine (like a new filter reading).

Looking at pictures of the exterior of the Camaro fuel tank, I don't see much that would cause the noises from where they're emanating. I know there is a cross-over in there and that would appear to be the most likely noise location, but I have no idea why it would be so noisy. The fuel regulator pressure gauge says zero pressure. I might try cracking a line after shutdown to see if it's some kind of pressurized lines, like maybe the check-valve on/near the Fore Walbro pumps.

[TuneAFish]

No problem - it's an interesting issue if nothing else :-)

[stevieturbo]

The fuel in your tank, simply by quantity should never be able to boil, in fact it should be barely over ambient. Unless it's an extremely small tank with very little fuel in it, but then I'd expect starting/running problems if it did and it was boiling.

The fuel rails on top, and bolted to a hot engine, will of course be hot....as hot as that engine, aside from the cooling effect from the fuel inside.

It is an odd noise though.

As a test when you hear it....you could disconnect the return close to the engine after the FPR ( if that's your setup ) and route a new line into a decent sized jar and run it for a few seconds to collect some fuel.

Simple way to establish fuel temperature, is fit a sensor wherever you want to monitor the temp and log it.
Thermocouple would be faster, most coolant type sensors are very slow. But as fuel temp will never really change that fast, it's still fine.