fuel tank vapor pressure

[Cowboy_Customs]

I was working on the truck last week, and outside air temp went from 29* in the AM, to around 60* that afternoon. Left part of the throttlebody torn down and the in tank pressure on the driver side was sooo much from the temp change that it forced fuel through my fuel system, and leaked maybe 2 GALLONS of fuel into my engine via the torn apart TBI. Hydrolocking my motor, and requiring me to change the oil. 

My question is this, shouldnt there be a vent or something to prevent the intank pressure to become this much? The tank still had pressure in it when I pulled the cap off it! What gives??

[VileZambonie]

Nothing gives. Anytime you open the fuel system not only must you relieve line pressure but remove the tank cap. If you have atmospheric pressure on both sides the fuel won't flow and cause the flood you had.

[DnStClr]

There is a vent on my fuel delivery hose. I thought it was a protection against overpressure too,like Cowboy Customs. We learn a lot around here..