Pressure build up in fuel tanks anyone? - Alfa Romeo Forum
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Pressure build up in fuel tanks anyone?

I experienced some some starting problems over the last couple of days - especially when cold. Put some diesel in and when I released the cap there was a massive blast of air/fumes that came out. Since then no more starting trouble. I assumed that the spring mechanism in the cap is a pressure release valve of sorts, so I flushed it out with brake cleaner and agitated the spring somewhat.

Are there other possibilities in causing this problem, has anyone experienced/cured it?
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My petrol tank always has pressure in it when I come to fill up ..
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There is no reason for your tank to be pressured. It is more likely for your tank to be sucking air into a vacuum rather than pressure of fumes rushing out. I have drilled a small hole into petrol caps before with no problems.
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Not sure how the Diesel tanks are vented.
The Petrol tanks are sealed (no vent in the cap) and are vented via the charcoal canister at the front of the car. Petrol vapour ending up getting burnt in the engine.
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The tank is not really sealed. The cap is valved so that air can enter but not escape.
I had a problem with the valve in the cap getting stuck. Result is that the tank would literally crumple because of the reduction in pressure. Had to take the cap apart to clean it.
But as said above, this should not cause fumes escaping.
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