Fuel Tank Pressure

[crazpony]

Is it normal for the fuel tank to build up pressure to the point that when the cap is loosened get a large rush and you can heard the tank contract?

[gmctd]

Yes - in summertime it can be about 2ps, set by the valve in the cap - what you're seeing is the excaping air volume of the tank above the fuel.

Wintertime will usually be a vacuum at about 4"hg, equiv of 2psi - again. it's the large volume of the tank that is venting.

[noelb]

The fuel caps have a filter under the black handle. This can get blocked. Gas and diesel caps have different valving pressure. Caps are cheap in the USA - $6-7. Sounds like a bit too much pressure or vacuum. You may want try a new cap. Mine was blocked to the point I believe it was contibuting to a starting problem. I paid $40 USD to get new cap here in Australia.

[Bnave95]

Good or Bad,not sure. Still I went and drilled a 1/16" hole in my cap.