Military fuel cans swelling (1 Viewer)

[concretejungle]

Not sure if this is the right forum to ask this question, but I'm having an issue with carrying extra fuel on the rear bumper during the summer. I'm using military fuel cans (plastic). The heat is causing them to swell to the point they look like they are ready to explode! I can't even vent them without fuel wanting to shoot out. This has been happening all summer, even when it's not that hot outside. It doesn't happen in the winter.

Last trip I almost couldn't get the water can out that was mounted beside it because the fuel can had swollen so much it was pressing on them and locking them in the basket.

Anyone else having this happen and have a solution?

 

[McDuff123]

Maybe vent more often, specially early in the day to let the heat-induced pressure bleed off?
Also, if gaining altitude they’ll expand…vent a few times as you’re climbing

 

[80t0ylc]

The gasahol that most stations are selling IMHO is responsible for a lot of heat related issues. Not that the older "pure" gasoline doesn't have heat issues, but I've noticed that when ambient temps get above 85*F I need to loosen my fuel cap because the OEM charcoal canister (and a replacement attempt) can't vent the fuel system adequately since adding an aux fuel tank. It was so bad after aux was 1st installed that both my fuel tanks swelled to the point of hearing the tanks flex as the pressure was released. That could've caused a tank rupture. You might check out the last post in this thread by @John McVicker, what Rotopax told him to try.

 

[concretejungle]

thanks for the replies. I have tried to vent them before but the instant that I break the seal on the lid gas starts leaking out of it continuously.

 

[e9999]

my steel NATO cans will also swell a bit in the sun, although not as much as plastic of course. Not much you can do I think. If you vent, may be OK for a bit, but eventually there just will be more liquid gasoline turning to vapor and you're back to the same point shortly. Why is it spilling liquid when you vent?

 

[Corbet]

I put ethanol free in my Scepters but in high heat they will swell in the sun. Especially since I fill them in town then drive home to higher altitude. Vent them at night and don't over fill them. I've never had issues with fuel purging when I vent.

 

[concretejungle]

I put ethanol free in my Scepters but in high heat they will swell in the sun. Especially since I fill them in town then drive home to higher altitude. Vent them at night and don't over fill them. I've never had issues with fuel purging when I vent.

maybe I'm over filling them?! I do fill them almost to the top so there's not much room for air.

Yes, when they swell if I crack the lid just a little, gas starts leaking down the sides of the can and will not stop until I tighten the lids.

 

[Corbet]

I’ll sometimes get that little coating down the side but have generally attributed it to fuel on the inside of the cap from transporting getting pushed out from the pressure equalization. If they have been stationary for a while it’s very minimal.

 

[concretejungle]

I had an experience where I took my dad on a camping trip and we stopped at a rest stop. he noticed the gas can was swollen and decided he needed to vent it. I turn around and gas is leaking everywhere and running down onto the exhaust pipe! I about lost it.

 

[Corbet]

Yah nothing like that for me.

 

[kwon-offroad]

maybe I'm over filling them?! I do fill them almost to the top so there's not much room for air.

You're WAY overfilling.

 

[John McVicker]

^^^
Not according to RotoPax. I fill mine to the brim…at home…all the way to the top. That’s what they suggested & it definitely helped.

I know, mines a RotoPax, but the principle is the same.

 

[kwon-offroad]

^^^
Not according to RotoPax. I fill mine to the brim…at home…all the way to the top. That’s what they suggested & it definitely helped.

I know, mines a RotoPax, but the principle is the same.

You win. @concretejungle overfill that sucker to the brim as @John McVicker confirms.

 

[iptman]

I tried venting my Sceptor fuel cans when I saw them buldged out one day this summer. I always put exactly 5 gallons in since I'm usually filling several cans at once and I can count and keep track easier by 5s. A coupe spilled a bit of fuel but several didn't. When I went back and saw them the next morning they were all concaved like a chubby dude sucking in his belly at the pool. Having vacuum inside the cans didn't strike me as a good idea either so I vented them again and just moved them to a place in my shed that doesn't get hit by the sun if I leave the shed doors open.

 

[e9999]

my vague recollections of physical chemistry tell me that the vapor pressure of gasoline is a strong function of temperature. Basically, IIRC, that means that at a given temperature, some amount of gasoline will vaporize and the pressure in the can will adjust until there is thermodynamic equilibrium between the liquid and vapor phases. So, if the ambience and liquid are at, say, 100F and you vent then close, the gasoline will vaporize until the pressure in the can is that one corresponding to 100F, I assume more than atmospheric pressure (don't know that for sure). The can may then bulge some. Then, after that, if the temperature goes up, the pressure will increase and the can will bulge more. OTOH, if the temperature decreases, the pressure will decrease, possibly below atmospheric if cold enough, and the can walls can be sucked in, so to speak.

I say, let the can do its thing... If the can is well-designed and in good shape, it should be fine.