Fire Hazard
HHHHMMMMMMMMMMM Been using this method for years, and have never noticed any swelling from heat expansion. Never had a problem. Maybe it's dependent on the brand. I use Castrol, in everything, and it comes in white bottles. Some brands come in black, which would get much hotter than the white. Whatever, it works good for me. I only do this when I plan on being out and about long enough to use the fuel in the built in tank and have to add. So the quart of gas most of the time isn't on board, and when it is, is only there for a few hours. I do not use the quart oil bottles for normal storage, and only fill them about 3/4 when using one.