Bubbling gas & expanding gas tank

[MuncyBob]

I've never had the dreaded vapor lock situation...actually have never had any real problems thus far. Last night after cutting the grass for almost 2 hours in 80 degree ambient air temp I noticed a hissing from the gas cap after shutting the PT down. Upon loosening the cap a gush of air came out and I noticed the gas tank slighlty compress...I'm guessing it was expanded slightly from the compression. The gas was bubbling at the bottom of the gas tank where the gas line connects. I guess it's time to look at re-routing the fuel line or protecting it from heat, but my main concern is why after almost 200 hours does this suddenly appear? /forums/images/graemlins/confused.gif I've run the engine at full throttle for longer periods of time and with the PTO in hotter temps with no problem in the past...hmmm?

 

[MuncyBob]

I've never had the dreaded vapor lock situation...actually have never had any real problems thus far. Last night after cutting the grass for almost 2 hours in 80 degree ambient air temp I noticed a hissing from the gas cap after shutting the PT down. Upon loosening the cap a gush of air came out and I noticed the gas tank slighlty compress...I'm guessing it was expanded slightly from the compression. The gas was bubbling at the bottom of the gas tank where the gas line connects. I guess it's time to look at re-routing the fuel line or protecting it from heat, but my main concern is why after almost 200 hours does this suddenly appear? /forums/images/graemlins/confused.gif I've run the engine at full throttle for longer periods of time and with the PTO in hotter temps with no problem in the past...hmmm?

 

[Gravy]

Sounds like the gas cap vent may not be working properly. It's probably supposed to relieve pressure or vacuum beyond a certain point (maybe 1psi or so?). A bit of pressure on a hot day is likely normal, but a gush of vapor might indicate a problem. You can probably match up a replacement cap at your local NAPA or other real auto parts store. I'd try to find one with a very low pressure relief setting, or even an open vent.

Gravy

 

[Gravy]

Sounds like the gas cap vent may not be working properly. It's probably supposed to relieve pressure or vacuum beyond a certain point (maybe 1psi or so?). A bit of pressure on a hot day is likely normal, but a gush of vapor might indicate a problem. You can probably match up a replacement cap at your local NAPA or other real auto parts store. I'd try to find one with a very low pressure relief setting, or even an open vent.

Gravy

 

[MuncyBob]

I suspected the cap...but does that explain the bubbling in the bottom of the tank?

 

[MuncyBob]

I suspected the cap...but does that explain the bubbling in the bottom of the tank?

 

[Phils]

My cap had a pressure/vacuum relief, but I defeated it while attempting to solve that vaporlock problem. I doubt your cap has changed or suddenly started to malfunction. The hissing was the cap doing its job.

The bubbles coming out of the bottom of the tank indicate gas vapor being generated, which is pressurizing the tank of course.

Both of those points you already figgered out. More importantly, it's not killing your engine and forcing you to take beverage breaks (yet).

And the big question you've already voiced: why now!??!?

My guess is a lower quality of gasoline in your area. Here in northern CA it didn't matter what brand or octane I tried, it all acted the same. But refiners are switching to "summer blends" now, and this summer's blend for your area could be more volatile than before (is that the right term? "boiling point" didn't seem like the best term for gasoline).

Even though I've moved my fuel system to the right side away from the exhaust, I'm still getting some VL, it's just not killing the engine nor bubbling up into the tank. I can hear the electric pump and the sound is different whether it's pumping liquid or fumes. It happens now after I've been working awhile and then shut down for 5 minutes then go to restart.

On hindsight I'd follow the suggestion of buying and installing some of the high-dollar fuel line insulation made for racing. (Can't remember who tried that successfully at the moment and it's too close to "go-home-o'clock" to look back -- BobRip or TracDoc if I was to guess but that's probably incorrect).

I have learned that there is a chain of events that occurs: once the fuel starts to VL, then the engine starts to run more lean. Running lean causes it to run hotter. Running hotter causes more VL. More VL causes it to run hotter.....

Although I haven't had mine die from VL since the last mods, I'm not done. Actually, I think some of that fuel line insulation could eliminate the last of my problem. I can't remember how many feet come on a roll, but if you find a deal and wanna split it, I'm game.

Phil

 

[Phils]

My cap had a pressure/vacuum relief, but I defeated it while attempting to solve that vaporlock problem. I doubt your cap has changed or suddenly started to malfunction. The hissing was the cap doing its job.

The bubbles coming out of the bottom of the tank indicate gas vapor being generated, which is pressurizing the tank of course.

Both of those points you already figgered out. More importantly, it's not killing your engine and forcing you to take beverage breaks (yet).

And the big question you've already voiced: why now!??!?

My guess is a lower quality of gasoline in your area. Here in northern CA it didn't matter what brand or octane I tried, it all acted the same. But refiners are switching to "summer blends" now, and this summer's blend for your area could be more volatile than before (is that the right term? "boiling point" didn't seem like the best term for gasoline).

Even though I've moved my fuel system to the right side away from the exhaust, I'm still getting some VL, it's just not killing the engine nor bubbling up into the tank. I can hear the electric pump and the sound is different whether it's pumping liquid or fumes. It happens now after I've been working awhile and then shut down for 5 minutes then go to restart.

On hindsight I'd follow the suggestion of buying and installing some of the high-dollar fuel line insulation made for racing. (Can't remember who tried that successfully at the moment and it's too close to "go-home-o'clock" to look back -- BobRip or TracDoc if I was to guess but that's probably incorrect).

I have learned that there is a chain of events that occurs: once the fuel starts to VL, then the engine starts to run more lean. Running lean causes it to run hotter. Running hotter causes more VL. More VL causes it to run hotter.....

Although I haven't had mine die from VL since the last mods, I'm not done. Actually, I think some of that fuel line insulation could eliminate the last of my problem. I can't remember how many feet come on a roll, but if you find a deal and wanna split it, I'm game.

Phil

 

[MuncyBob]

I never realized there was a difference to the gasoline between winter and summer until these discussions...didn't hit me until reading your response since we have only had a few really warm days recently. I'll be searchng for that fuel line insulation, seeing the fuel bubbling like that makes me somewhat uncomfortable ...maybe we can get more PT owners to go in on this, might reduce the cost somewhat. /forums/images/graemlins/confused.gif

 

[MuncyBob]

I never realized there was a difference to the gasoline between winter and summer until these discussions...didn't hit me until reading your response since we have only had a few really warm days recently. I'll be searchng for that fuel line insulation, seeing the fuel bubbling like that makes me somewhat uncomfortable ...maybe we can get more PT owners to go in on this, might reduce the cost somewhat. /forums/images/graemlins/confused.gif