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How do I make my fuel cap fully venting? I bought what was suppost to be the correct one from GM, but it still holds vacuum in the tank.
 

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Simplest way? remove the O-Ring in the cap at top of threads.
 

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I learned this the hard way after taking a dremel and removing the plasctic center, spring and plunger in the cap of my original.
 

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I used a Harley Sportster cap I had laying collecting dust. I had drilled 4 small holes in the center plastic when I was racing the Sportster. I can blow both ways through it with no restriction.
Ted
 

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vaccum in the fuel tank

How often does this happen to these trucks. Is this a rare thing or should everyone try to vent the tank cap? I never heard of this before. Gasoline cars usually develop pressure in the tank instead of a vaccum, I think. Why does Diesel have a vaccum?
 

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gas forms pressure due to the volatility of it. try pouring gas on the ground, pour a likewise amount of diesel on the ground and wait 2 c which one evaporates into the atmosphere 1st. evaporating causes expansion by turning into gaseous versus liquid form. and it happens faster with a sloshing tank. it's also why the oil industry put those little rubber cups on the fuel nozzle when filling up. they slow the transition from liquid to a gaseous state.
 

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How often does this happen to these trucks. Is this a rare thing or should everyone try to vent the tank cap? I never heard of this before. Gasoline cars usually develop pressure in the tank instead of a vaccum, I think. Why does Diesel have a vaccum?
FAQ's
 

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How often does this happen to these trucks. Is this a rare thing or should everyone try to vent the tank cap? I never heard of this before. Gasoline cars usually develop pressure in the tank instead of a vaccum, I think. Why does Diesel have a vaccum?
FAQ's has
 

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How often does this happen to these trucks. Is this a rare thing or should everyone try to vent the tank cap? I never heard of this before. Gasoline cars usually develop pressure in the tank instead of a vaccum, I think. Why does Diesel have a vaccum?
FAQ's has a l
 

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How often does this happen to these trucks. Is this a rare thing or should everyone try to vent the tank cap? I never heard of this before. Gasoline cars usually develop pressure in the tank instead of a vaccum, I think. Why does Diesel have a vaccum?
FAQ's has a link
 

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How often does this happen to these trucks. Is this a rare thing or should everyone try to vent the tank cap? I never heard of this before. Gasoline cars usually develop pressure in the tank instead of a vaccum, I think. Why does Diesel have a vaccum?
FAQ's has a link on
 

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How often does this happen to these trucks. Is this a rare thing or should everyone try to vent the tank cap? I never heard of this before. Gasoline cars usually develop pressure in the tank instead of a vaccum, I think. Why does Diesel have a vaccum?
FAQ's has a link on that
 

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How often does this happen to these trucks. Is this a rare thing or should everyone try to vent the tank cap? I never heard of this before. Gasoline cars usually develop pressure in the tank instead of a vaccum, I think. Why does Diesel have a vaccum?
FAQ's has a link on that very thing.:)
 

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Or for the simplest, no cost solution, dont tighten the cap down fully.

I simply screw my cap down about 1 turn and the close the fuel door. Cap cant fall out, and the tank is vented.

I am all about cheap and easy.

Tim
 

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The cap should have a vacuum disc inside. It will keep a slight vacuum and a good bit of psi. Clean the threaded surface and try to suck and blow through it. You might be surprised how easily it flows in. The thing is, MANY have started to realize that it is pressure not vacuum forming in the tank most times.
 
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