stihl gas caps with very slight leak

This is the first time I had a problem with them and its 2 saws at once,never did it before or least I never noticed it if it did happen.I talked to a guy who works for stihl and he said he thinks it has something to do with using my saws out in the cold and then when I bring them into my basement where its much warmer it builds up a lot of pressure in the tank and that's why its seaping some gas out.I don't know if that's what's going on but it does only seem to be happening when I bring them in from out working in the cold,they don't leak at all when I'm out working but I bring them in and a couple hours later they got gas coming out.

 

Something similar happens on my motorcycle in the summer. If I fill it to the brim with fuel, and leave the bike parked, it will start leaking after an hour or two. It has to do with the expansion of the fuel. It's cool in the ground, maybe 60 something degrees, but warms up rapidly on a 90 degree day once it's poured into the tank.

It seems if you have a half tank of fuel and bring the saw into the house, it can't expand enough to leak. Unless of course the tank vent in the saw fails.

 

No. I have a 390 thats about 10 years old. Cap doesnt leak. Saw use to out of a cracked fuel line. But I fixed that when found. If it leaks now I dont notice it. Its the only stihl I have with flippies

 

There is a tank vent though?

 

Yeah there's a vent but I guess on the new saws it's only to let air in from what the guy was telling me and going from big temp changes is building pressure in there and that's what I'm seeing,i don't really know but I just started noticing it and its on multiple saws.he also mentioned about different gas because I guess some can be more prone to build a lot of pressure in there?

 

Here we go on fuel. Bit I only use non e fuel.