It's amazing more of these things don't explode

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Sep 19, 2008
Central Texas
This past June I was in SW CO checking out where the gold-king mine spill happened. Long, steep, uphill section.. I start to smell fuel vapors. A few months before the date in question I tried rebuilding my factory Charcoal Canister and the valves still stick, so I threw in a VC120, and it fixed the fuel smell around home. But in the mountains? whole different ballgame.

So I smell the vapors. Park the truck. Pull the fuel door latch. Unscrew the tap and WHOOSH, along with a sputtering of liquid fuel coming out. Here's the thing. the flow didn't stop. It kept going. And going. And going. along with a gurgling sound.. distinctly like BOILING.

So I grabbed a video. Keep in mind this is after literally 3-4 minutes of waiting for it to stop:

The fact that it wouldn't stop tells me fuel was literally boiling somewhere in the tank. I can't remember how full the tank was.. and yes, if it's full and venting pressure you'll get gurgling in the filler neck as that venting occurs. But this wouldn't stop. New vapors were being created at a high rate as quickly as they were venting.

So.. any ideas why? I was at somewhere between 11k and 12k feet. Less atmospheric pressure to hold back vapors? Tons of heat from the climb? (all heat shielding in place under the truck) This was clearly more volume than the charcoal canister was designed to deal with.

I ended up leaving the cap loose to avoid pressure buildup and a fuel tank crack that so many people talk about. Probably pissing into the wind.. I'm sure the pressure has been many, many times before and after. Also can't remember if it slowed down when I got back to town or a lower altitude. IIRC I was chasing a storm back to town so my focus was elsewhere.
Yep, happened to me in CO, at 13,000ft. Mine was actually shooting gas out and down the side of the truck. Just pulled the charcoal canister and left the line venting to atmosphere.....
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Last week we did engineer and cinimon pass. I could smell gas with my new vc120 charcoal canister.
I posted this same thing a few weeks ago after going to 10,000ft. VC120 CC here, and mine did the same thing. I've never had anything like this happen before. Full boiling noise, it took 10-15 minutes to fully vent out the gas filler, with cap off. Gas smell while driving. Not that fun.
I am no scientist but I think fuel evaporates and off gasses at a higher rate at high elevation. We drove our excursion to telluride once and had a bad gas smell when we got to town. The tank had a lot on pressure.
I ran all those areas for a week 2 years ago, never had a problem. I am still running the original vapor can and charcoal.
It's all 10% ethanol in CO. I gave up looking for convenient non-ethanol.

Some mountain towns have it or at least don't mark ethanol mix on the pump. I usually try an fill up once I get to altitude.

The wife's 90 4R doesn't have the fuel vapor problem, and her system is pretty similar. But a smaller tank.

The evap is high on my list of things I want to make better. That being said, I get some pressure in the tank, but never 5 minutes of venting liquid.

I live at 6k, and regularly visit 10-12k+ altitudes. And the truck loves the twice a year visits down to 2k elevation. I imagine that must be what the supercharger is like.
My Cruiser smells like an alcoholic all the time with that ethanol gas. I have heard the boiling as well. I would imagine ethanol boiling at a lower temp than gas but I'm no chemist.
I replaced my original charcoal cannister with a new stock Toyota one right before I went to Ouray a couple of years ago and had no problems at elevation. I was having problems in Dallas beforehand. A new cannister does help!
Likely not actually boiling but offgassing at an extreme rate due to elevation change. Think of a bottle of water, at sea level you drink half and the bottle is pliable and easy to squeeze, now go to 4000ft above sea level with the same sealed bottle. The bottle is firm and difficult to squeeze, fluid volume is affected by atmospheric pressure, or at least at the molecular level. Think of that hiss of gas that comes out when you open a non-carbonated previously unsealed bottle as you climb in elevation, now add this principle to a fluid that on its own vaporizes at a quick rate if not kept in a pressurized/ sealed vessel. The evaporation is accelerated and the pressure doesn't have enough ventilation. You open the fuel cap and you're essentially speeding the process up further because being in a pressurized or sealed environment has retarded the process. It reminds me of the boiling cup of water in the microwave. The water looks still, it hasn't come to a rapid boil yet, so you go to take it out, as soon as you move the cup you excite the molecules and the boiling water explodes like an erupting volcano.
I think that ^^^^ is possible, but I really don't think it's what happened to my truck and doesn't look like what is going on with bloc's

I had my dad with me who has been around cars a long time and he was amazed. It really went on for a good 5 min. There is no way it is just escaping gas given the size of the fill nozzle. The volume of pressurized gas needed to vent for 5 min would be massive.

I think it's a lot more likely that our sealed gas cap acts like a radiator cap, it pressurized the system. Then as you gain altitude you lower the boiling point. You have a lot of hot gas being returned back to the tank from a very hot engine compartment since speeds are usually pretty low. And then as soon as you unscrew the radiator cap, that gas that was kept below boiling point by all that pressure actually boils! And it continues to boil until it gets back below the at altitude boiling temp. It's actually quite scary and something to definitely be aware of.

Doing a quick search around the internet the boiling point of gas is listed frequently between 140-185, if that's at sea level I would imagine it's lower at altitude, and the returned fuel from the fuel rail is easily going to be over 100, our engine bays get awfully hot.
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Vapor pressure of ethanol gas can be around 10psia, which is right around atmospheric pressure at 10,000 ft. It's very likely that it was vaporizing or boiling at those conditions. I'm curious how much pressure the stock tank is intended to maintain. It wouldn't take much to prevent this, at least until the cap is opened.
It's hard to know the exact boiling point of gasoline, as mixes change for the seasons, areas etc. But, it can be below 100f. I do know, I've run all these areas and not had a problem like what is described here.

Unless someone is willing to inspect everything in their evap system, I would suggest just living with it. I also wouldn't release pressure from the tank, but that is just me... And no, you won't blow anything up.

My proposed solution is not allowing people from Texas into the San Juans until we figure it out for good. :flipoff2:
One variable, keeping our tank topped off. I kept my tank constantly topped off, smelt gas but didn't have any problems like the previous posts above. Professors chime in.
Same thing happened to me after hours of driving in Death Valley with 110 degree heat(no that was not smart) and I can hear gas boil. I let it vent for a little bit but gas is so hot and boiling so I just put the cap back on and let it cool down. Once cool then no more gas venting but it was definitely a bit scary. The pressure was so high it almost blew the cap out of my hand and the air was so hot I can't keep my fingers near it, y one spark and it could of been disaster.

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