Fuel Tank Venting and the Charcoal canister
By Charles Goin (Additional thanks to Rodney Davis)
Ever notice that when you fill up the tank of your GT that it starts to smell of gas? Also notice its
not just temporary, it can last for a good long time up to say a ¼ tank of gas or more. Have you
looked everywhere and have not been able to find the source? Have you ever wondered where
those hoses to the canister are supposed to go and why? Well let me fill you in on how to do this
and where the hoses all go. Seems that Opel wanted to keep it a secret and never really gave any
of us a good guide line on any of it.
I personally ran into this problem just recently and Opel GT Source sent me a fax
immediately, of an old tech tip from Rodney Davis of the North American Opel GT Club (now a
chapter of OMC) . Rodney is unfortunately no longer with us, but his tech tips and advice are.
The Opel GT has an intricate fuel venting system built into the rear of the car and is
mounted above the gas tank in the back under and behind the spare tire platform. What happens
is this, the plastic tubing that makes up this system becomes brittle with age and starts to break
apart and fall into clumps of hoses on top of the tank.
The venting system for the fuel tank consists of inlet tubes at diagonal corners at the top
of the tank. These tubes are in turn connected to the fill pipe of the gas tank via a 2 – 3way tees
and the plastic tubing aforementioned earlier in this article. The venting system is there to allow
air into the tank to avoid a vacuum as the car uses its gas supply and also to vent the tank when
heat expands the gas vapors in the tank as well. The clear plastic used by Opel for this system is
obviously not designed to deal with the high temperatures of the car or the long-term exposure to
gasoline fumes.
The fix for this is quite simple though. Use standard reinforced 3/8 or 5/16 gas fuel line, 5/16 works
better, but 3/8 is easier to get sometimes. In addition replace the two fittings with 2 – 5/16" tees
available at any parts store. Also make sure to get the small hose clamps to clamp off each
connection. This way you will never have to fool with this again. One note though, you will need to
drill the hole that the vapor return lines goes trough the body at, just a hair bigger, since the fuel
line is larger than the original material.
DO NOT try to cap that line off. You will develop a vacuum in the tank and it will cause the car to
stall. You will have to use a coat hanger to feed the fuel line through the body and up from under
the tank. I found it easiest to do this with the rear tail light lenses out, it helped me when I was
trying to fish the line up.
As for where the lines go, the line that vents the tank runs down the body and to the middle port
of the carbon canister. If you still have a Solex. This is how things hook up. (See picture). The
small bottom hose of the carbon canister goes to the Solex fitting at the base of the carb pointing
at the valve cover, the large one goes to the fitting on the Solex at the top of the carb facing the
valve cover as well. If you do not have a Solex, get a large cap and cap off the large fitting on the
carbon canister and leave the other one open to the air and hook up the line coming from the tank
to the canister. While you don’t need the canister at all really, leaving it there and having the one
tube hooked up looks a little neater and at least it will look like the canister is doing something.