Fuel tank building pressure

[USMC6062]

I just picked up a M923A1, I drove it from NC to FL. It ran an operated flawlessly, the only thing I noticed was the fuel tank was building up pressure every time I stopped for fuel. Is this normal? It seems like the tank should be vented. The truck is one of the ones completely refurbished by red river. I couldn't find an answer on here.

 

[TurboMustang370]

Building pressure or creating vacuum?

 

[goldneagle]

Easy problem to fix. I had the same thing on mine. **** mud bugs plugged the vent tube at the top of the intake stack. Used a drill bit spun by hand to break up the blockage. You can also remove the 2 vent tubes from the top of the fuel tank and see if they are clogged. Two 1/4" tubes going to a splice block and a 3/8" tube from there up the side of the intake stack.

 

[USMC6062]

Just checked the vent tube up top, it did have signs of mud dobbers. It wasn't blocked solid though, I'll have to pull the vents loose from the tank and blow air through the lines and go from there.