pressure in gas tank....

[rausken]

As title says just got my corvette 85 c4 and it seems to be building pressure up in the gas tank when I drive anyone have this problem?

 

[CCO]

Same with my '94. I chalk it up to a temp change either up or down causing the fuel to expand or contract.
Colin.

 

[Range]

How do you know it builds pressure?

 

[CCO]

How do you know it builds pressure?

When unscrewing the fuel cap, I can hear either suctions or pressure release.
C.

 

[Riley P]

Funny thing, I was doing a little internerd surfing and it turns out there is a vented and non-vented cap for the 84-92 C4. I never did find an answer to which one was correct.

 

[CCO]

Mine must be non-vented -- Hoping it's functioning properly.
I never thought that this could be a problem since I've experienced tank pressure buildup in other cars.
Worth me asking around to get some info.

C.

 

[vintageracer]

My gas cap gives a "puff" when I remove it to fill up. Mine is an '87.
Don't recall what my "project" '85 does.
David

 

[foxtrot]

My 93 also release's air when cap is removed, always considered it normal.

 

[Range]

Is it pressure, or vacuum? Start with a full tank, drive around until it is empty, you would assume it is vacuum created by the void......but if you say it is pressure, then who am.I o argue.

 

[Keith Tedford]

Tank Venting

I don't know about Corvettes, but the old Chevelles and the gas filler behind the license plate and if it had a vented cap, gas would come out when accelerating. These tanks had a vent tube that came off the frame ad attached to the floor pan up higher and a non-vented cap. The station wagons and el Caminos had the old conventional gas filler door up higher and these had a vented cap. What the new cars have, might be something similar. I would think that, one way or another, that the tank should be vented. Now, that sure in enlightening.

 

[VikingTrad3r]

my 87 whooshes when opened.

 

[rausken]

its vacuum

 

[Dave91TM]

Hi Guys

My 91 has always released "pressure" when I open the gas cap. Never been a problem, never questioned. Is it perhaps that the system is sealed due to an emissions requirement?

 

[rausken]

it is vacuum

 

[XFIRE82]

fuel is pumped from the tank to the engine via the electric pump in the tank. There is a return line from the engine back to the tank. The tank needs to be vented. As fuel is returned back it is natural for some pressure to build up in the tank but is vented either with a breather pipe or a cap that lets it go. There is no vacuum in the tank. So if you hear the release of air when unturning the cap then that is normal.