fuel tank pressurizing!!!!!!

[Ryuronich]

When it gets cold my fuel tank is pressurizing. u can here it hiss out of the rollover valve and when u take the cap off u get a wosh of air. it only does it when its cold whats going on?

[Mopar1973Man]

Ekkk... Bad injector copper shim or maybe a cracked head.The bad copper shim would allow the compression gases to be forced into the return rail to the fuel tank pressurizing the fuel tank. I've heard of a person with a cracked head and only cracked between the combustion chamber ot the return rail.

[Ryuronich]

why would it only do it when its cold not at all this summer im hopeing coper shims

[LiveOak]

Are you sure you are not hearing the hiss of a vaccum that has built up in the tank? This would make nearly the same symptoms. The fuel is heated as it goe through the fuel filter cannister. Eventually the fuel reaches a stabile temp. and expands a proportionate amount depending upon the fuel mix, temperature, elevation, and other factors. The fuel can expand in volume nearly as much as other oils of nearly 10% of its volume. You park the truck when done and it sets over night. The fuel cools and contracts due to the cooling and a vaccum is created. The fuel filler cap should have a pressure relief vent in it. The roll over valve prevents fuel from leaking out, not vaccum. This would not relieve vaccum pressure though. Anyhow, that is my theory. Does the fuel tank do this with a full to the tip top fill?