Vented gas caps are supposed to allow air to enter the tank as fuel is
consumed, but are not supposed to exhaust fuel fumes to the atmosphere. The
cap design, along with the location of the vent holes works like a one way
valve to accomplish this. It is normal for there to be a slight pressure
build up inside the tank on a hot day that will vent when the cap is opened
to refuel. Just like your sealed gas can in the garage. The problem is
that if air can't enter the tank during use, there comes a point where the
fuel pump cannot overcome the vacuum inside the tank, causing the car to act
like it is out of gas.
David Riker
davriker@digitalpath.net
http://community.webshots.com/user/fool4mg
http://www.myspace.com/fool4mg
----- Original Message -----
From: <JMFarley50@aol.com>
To: <spridgets@autox.team.net>
Sent: Sunday, May 20, 2007 11:25 AM
Subject: Gas Tank Venting
> As I can see, the only place the gas tank in my bugeye can vent pressure
> is
> through the gas cap. In checking out the bottom of the cap, there are
> two
> small holes near the center and two more holes near the outer radius,
> past the
> rubber gasket. I assume these holes accomplish the venting. The problem
> I
> have is pressure building up. I found that when on the cap also seals
> tightly
> against the rubber collar fitted between the body and the filler tube, so
> the cap can't vent even if it wanted to. I have verified that the tank
> is
> tightly secured and the rubber collar seems to be in place correctly.
> Looks
> like my next step it to trim the top of the rubber collar to create a gap
> to the
> cap. Before doing so, I wanted to check my logic with the group.
>
> Thanks, John
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