MSR fuel bottle failure in extreme cold

Sounds like a basic physics problem : PV=NRT.  Temperature drops, internal pressure decreases.  One solution is to fill the bottle all of the way up, that minimized V.  The problem will get worse as the bottle empties.  Note: this only really applies when closing the bottle a room temp and taking it to cold conditions.  Another ( and even easier solution) is to leave the bottle and fuel outside BEFORE your trip and then fill and seal in cold weather.  Just a thought.

Maybe the child resistant cap is the problem?

With water bottles when it gets cold, the cap freezes. Maybe that’s the problem.  If there’s any water. If I don’t tighten the cap completely it helps.  Although you don’t want fuel leaking

A decent in altitude can also do that. Happed to me long ago. Had to climb back up. Some pry it up but damage can occur.

What stove do you use?

If it’s a system with a bottle mounted pump then leave the pump on all the time.

If I need more than one bottle I store the spare pump(s) on at least one more bottle. Then I can always heat water to fix any stuck regular caps.

Maybe it is pressure change from pv=nrt vacuum issue. However, I suspect the tight lockup is due to very different coefficient of linear thermal expansion for the threads in aluminum neck vs polymer cap.  Once tightened, a big reduction in T will produce different dimensional changes for the 2 disparate materials, causing an “interference fit” with very large forces in the threads.

I’ve had to use a tent stake for leverage through the cap finger hole.

If this root cause analysis is correct, retightening a very cold cap against very cold aluminium would require only normal untightening force, but the seal might be more prone to seepage after warming up.

Be really unpleasant, but what if you stuck the cap/neck in your armpit for ten minutes?

MRS sells a non-childproof cap (which used to be the standard style cap before they were deemed dangerous around children) called the Expedition Fuel Cap. I don’t know when the child safety cap became standard, but it was at least a decade ago. This optional cap has always been easier to open when temp and pressure variables make opening a wrestling match. I’ve easily removed these caps at -40. BTY, the old style cap is much easier to inspect for gasket wear and cracking.

Thanks everyone for the great responses – all very helpful.  I did see the “expedition cap” alternative online when researching this issue.  The name suggests MSR know they have a problem with the safety cap in more extreme conditions, and I noticed MSR recommends customers try it after they complain about the safety cap.  (I wish MSR had the integrity to warn clients in instructions, so we don’t learn it, after we’ve bought their product, in the field).  I only had one bottle with me, but I took it out twice, and with my bottle it was impossible to open the safety cap until the fuel bottle was warmed substantially.  I’d guess it was threading issues discussed above rather than pressure change, but I didn’t have time to experiment.  In either case I’m pretty sure I could resolve the issue by putting it in my sleeping bag in an emergency.

I suspect MSR was forced to use childproof cap – either legally or from regulations

I suppose you could have the bottle lying around and a child could get into it.  You wouldn’t want them exposed to the chemical and the house to burn down.

They could sell the bottle with the childproof cap and include the original cap.  Or have a warning on it that it’s hard to open when very cold.

sterno ; i commonly bring along a small can of sterno. that way, if real cold, once i get into the tent, if i can make any flame at all, things/hands will get warm. that way, if your bottle was temp locked, you could just warm the aluminium up a bit, and it should probably release.

on the water bottles freezing up, the yellow top ones from 40Below pretty much solve the worst of that issue.

cheers,

v.

peter v knows whereof he speaks, like few of us can imagine.

I replace all my MSR bottle caps with these—and when stuck I use a tent peg inserted to twist it off.

How about putting some silicone “grease” on the O ring? Even some Vaseline would likely work.

That ring top cap looks like your answer. I have one from The Dark Ages before we cared much about protecting stupid kids from themselves. In those days we believed in the Darwin Awards.

I agree with Eric. Some silicone grease would be excellent. Not only will it help the O-ring to seal, but it will significantly reduce the friction. My limited experience suggests that really cold O-rings don’t slide very well.

Not so sure about the change in dimensions due to temperature. The TCoef for any plastic I have looked at is larger than for Aluminium, so in cold weather the plastic stopper should shrink more than the Al neck. It should get looser. But the change would be very small.

Cheers