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. :rofl:
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.

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.
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.
Last edited:
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.
Old Thread: Hello . There have been no replies in this thread for 100 days.
Content in this thread may no longer be relevant.
Perhaps it would be better to start a new thread instead.

Similar threads

Users who are viewing this thread