Fuel vent line rethink.

[First opel 1981]

I have been debating on whether or not to leave this issue within the thread on fuel vent lines but think it deserves its own thread.

I was running the fuel vent lines on my 73 GT and noticed something that I, personally, think is a major issue.

I was using the diagram from http://clubs.hemmings.com/clubsites/...h/TankVent.pdf and realized that when the fuel tank is full, or close to full, there would be a tendency for liquid fuel to enter the vent lines, only to be expelled to the charcoal canister. I don't think this is what was intended.

I have made a small modification to the vent line routing and, again personally, feel this is how the fuel vent lines should be run.

Here is the original
Attachment 21476

And here is the proposed revision
Attachment 21477

I believe this small change will prevent any liquid fuel from venting from the fuel tank.

Anyone who has noticed a fuel smell from the front of their GT, that they can't trace, might benefit from this.

Discussions are most welcome.

[markandson]

There is another thread here (and probably more) on this subject. There are a couple of really important points concerning the venting of the tank. First is the "T" that goes at the top of the whole system. This is not just a regular tee it has a very small orifice in the leg that goes up to the canister making difficult for any excessive amount of liquid to go forward. Secondly it also limits the amount of vacuum that the tank can see. The two vent lines from the tank are supposed to be attached at the top of the body just below the rear window.
If you get in where the tank goes and look up you will see bend tabs that are designed to hold the hoses. With the hoses that high above the tank the car would have to be upside down before any liquid could flow forward to the canister. HTH

[First opel 1981]

Originally Posted by markandson If you get in where the tank goes and look up you will see bend tabs that are designed to hold the hoses. HTH

I used to be able to fit in there. These GTs shrink over the years.

I understand what you are saying though. There is a big IF in there. The IF is if the fuel lines are run up to the body first and I see your point. The way I have them would essentially do that even if the lines are closer to the tank.

I never did like seeing the vent lines hanging from the base of the back deck. It looked a little clumsy to me.

Quick question, if you don't mind. Which way should the small hole be oriented. Towards the tank or towards the charcoal canister?

A side note: The way you describe the routing is the way I propose the diagram should be changed. This thread is dedicated to the change in the diagram and not solely about the routing of the vent lines.

[markandson]

Originally Posted by First opel 1981 I used to be able to fit in there. These GTs shrink over the years. I understand what you are saying though. There is a big IF in there. The IF is if the fuel lines are run up to the body first and I see your point. The way I have them would essentially do that even if the lines are closer to the tank. I never did like seeing the vent lines hanging from the base of the back deck. It looked a little clumsy to me. Quick question, if you don't mind. Which way should the small hole be oriented. Towards the tank or towards the charcoal canister? A side note: The way you describe the routing is the way I propose the diagram should be changed. This thread is dedicated to the change in the diagram and not solely about the routing of the vent lines.

The leg of the tee with the orifice in it goes to the canister.

[blancojp]

I have never had this type of problem since the first thing I do on any new Opel is to get rid of the canister.

I route the vent line upwards from the filler tube connection and then loop it down to a "tee" back to the vent lines in the rear of the tank. I believe the Manta and Asconas do the same route with their vent lines, at least the Ascona I have was done that way when I got it. As long as the vent line is rising to a point higher than the filler neck, fluid works its way back so nothing will go forward.

Considering the amount of cars I have built, I don't believe removing the canister is a big loss anyway.

[First opel 1981]

Originally Posted by blancojp I have never had this type of problem since the first thing I do on any new Opel is to get rid of the canister. I route the vent line upwards from the filler tube connection and then loop it down to a "tee" back to the vent lines in the rear of the tank. I believe the Manta and Asconas do the same route with their vent lines, at least the Ascona I have was done that way when I got it. As long as the vent line is rising to a point higher than the filler neck, fluid works its way back so nothing will go forward. Considering the amount of cars I have built, I don't believe removing the canister is a big loss anyway.

The canister is only for environmental reasons. What the charcoal canister does is trap (temporarily) gasoline fumes recovered from the venting of the fuel tank. When the car is running it is supposed to draw air into the charcoal canister and pull the trapped gasoline fumes (OK, technically chemicals) into the combustion chamber where it burns.

Removing the canister shouldn't hurt perfomance but you are then dumping raw gasoline fumes into the atmosphere.

Not on a soapbox by any means, just explaining the function of the charcoal canister as I know it.

[blancojp]

Originally Posted by First opel 1981 The canister is only for environmental reasons. What the charcoal canister does is trap (temporarily) gasoline fumes recovered from the venting of the fuel tank. When the car is running it is supposed to draw air into the charcoal canister and pull the trapped gasoline fumes (OK, technically chemicals) into the combustion chamber where it burns. Removing the canister shouldn't hurt perfomance but you are then dumping raw gasoline fumes into the atmosphere. Not on a soapbox by any means, just explaining the function of the charcoal canister as I know it.

Thanks for the info but like I said, no big loss.

[wrench459]

If your worried about environmental concerns. The last car you'll want is the 68-73 Opels. These where very dirty cars to start with. CO was set at 3.0% HC 400ppm and the evap. system was terrible.
By today's standards there "gross" polluters and need to be removed from the roadway.

[newman27]

Originally Posted by wrench459 ...By today's standards there "gross" polluters and need to be removed from the roadway.

Bite your tongue Dan!

[Nathan Acree]

Originally Posted by First opel 1981 The canister is only for environmental reasons. What the charcoal canister does is trap (temporarily) gasoline fumes recovered from the venting of the fuel tank. When the car is running it is supposed to draw air into the charcoal canister and pull the trapped gasoline fumes (OK, technically chemicals) into the combustion chamber where it burns. Removing the canister shouldn't hurt perfomance but you are then dumping raw gasoline fumes into the atmosphere. Not on a soapbox by any means, just explaining the function of the charcoal canister as I know it.

I am actually putting the charcoal cannister back on my car for a simple reason- Its keeps the garage from smelling like a gas can. Something to think about anyway.

[markandson]

I put a new canister in my car that came from another vehicle. I don't remember the application but I do have the part number of the canister at home if anyone wants it. The diameter of the new part is slightly more than the old one. I shaved the plastic down around the end and it was a nice press fit into the original end closure/bracket. The bracket that attaches it to the body was also too small so I cut an extra one that I had and welded a piece into the one I wanted to use, you can't tell what I did if you look at the bracket now after a little grinding and painting.

[First opel 1981]

After careful consideration and the desire to use my new tubing bender, I decided that I would re-do the gas tank vent lines so they will NEVER leak again.
Using 5/16 steel brake line tubing and a LOT of hose clamps, I ran the new vent lines in steel. The front vent can't be seen in the picture but it snakes under the package shelf support to the back of the tank where it goes up to the tee. I vented both the front and rear tank vents to a tee and then up to the neck tee. The neck tee is the highest point (as I am confident it should be) of the venting system. From there I ran a second tube down and out of the car to finally exit to the charcoal canister.

The steel lines might be overkill but I am certain I will NEVER smell gas in the car again.

tankventing.JPG

[markandson]

I hope you included the tee with the orifice in it, did you?

[First opel 1981]

Originally Posted by markandson I hope you included the tee with the orifice in it, did you?

Both tees have the original orifices.

I like orifices....