Hello Gentlemen,

I was wondering if somebody has an idea about my problem. When I got the car it had no tank as it was just running on LPG.
I got a new tank, Spectra 34e with 3 vent lines (72 CS). The tank came from US, so I have no idea if there might have been a transport damage. At least there was nothing I could see when I installed the tank. I connected the 3 lines to the standpipe as described in the CSM. As I have no more canister in the motor departement I just closed the left vent from the standpipe with a cap. First try was with approx. 20l of gasoline, everything was fine. Today I filled it complete (until auto-stop), then I went home. In the garage I remarked that it was heavily leaking. It was leaking from the left top front of the tank. My first thought was the the tank is leaking where upper and lower part is been put together, maybe due to too high fuel level and/or too much pressure (quiete warm here today) in the tank. Remember I closed the left vent in the standpipe where normally the vaporline is connected. When removing the fuel cap (vented one) even much more fuel came out, but there was no remarkable pressure in the tank. Then it stopped after approx. 5mins, no more fuel leaking. I took the car, went 100km in order to lower the fuel level in the car, went back home, same situation, but less leaking then before. Again, it stopped after a couple of minutes. Is it possible that -with a full tank- fuel goes into the left vent from the tank, so maybe I just didnt fix it sufficiently? I am wondering if the tank would be leaky, it would leak all the time and not just for a couple of minutes. Any idea/suggestion is highly appreciated as the last thing I like to do is to order another tank from US :-(
Thanks guys!

Regards,

Marc

 

My vent was melted from an exhaust pipe that was too close. It's situated ridiculously close to the exhaust. I solved this by installing a 90* brass fitting and making sure the new vent was high enough to not leak with a full tank. You might also check the other hoses for leakage. The area you describe was exactly where mine was leaking and it would not do it all the time. Hope this helps.

 

Are you using a vented cap?

 

I use a Gates 31670. it lets air in but not out. (Is this now vented or notvented...)

http://www.amazon.com/s/ref=nb_sb_no...ds=Gates+31670

Maybe I should add the information that i removed the left cap of the standpipe (to see if there is a difference) before I drove that 100km.

 

I have a cap just like that. I though that was vented to let air out if needed.

 

Hm. I am pretty sure when I bought it I tried and air just went into one direction, into the tank. Has it to vent in both directions?

Edit:

Guys, I am lost now. The CSM tells me that on all models a two step locking vacuum pressure type cap is used. Does it mean sealed? Or vented? As english is not my native language I am confused now.....I was in the garage, put the car on a jack and took a closer look. No more fuel is coming out. Hm??

 

I know if the vent lines are not high enough it will burp gas out of an over filled tank as the outside air temp rises. I fought this issue with mine and finally ended up looping the vent lines together. On a really hot day my tank will build some pressure and I relieve it by periodically loosening the cap.

 

I think because you plugged the vent line and removed the charcoal cannister you may want to replace it with the pre-cannister system they used. This consists of a short standpipe tube with the plastic vent on top. Otherwise you will continue to fight pressure leaks every time the tank warms up.

 

Starting in 1970 for California cars and in 1971 for all US cars, there was a carbon canister installed, usually behind the right headlight.

The fuel cap design was changed at this time to keep vapors from escaping (air can go in the tank but not out, as you described).

The carbon canister received pressure from the warm fuel when the car was stopped. The carbon adsorbed the fuel vapor. The fuel vapor was then desorbed and pulled back into the engine when it was running.

When you plugged the vent and used the sealed cap, there is no outlet to relieve the vapor pressure of the warm gasoline. This causes pressure to build up in the tank, which is not designed for this.

The simplest method to solve this is to use a fill cap that will allow air flow in both directions.

 

A vented cap lets air in not out. A non vented cap seals the tank filler.

 

Use the solution proposed by RROldSX. That was how the factory did it before 1970.

 

Is the vent cap you installed leaking? Is the stand pipe vented to atmosphere or just a loop? I'm not 100% familiar with your year model?

 

Sorry I do not have a picture of the installation but here is a pic of the vent. I suggest adding a 90* bend and a little longer standpipe on it to keep it away from the exhaust and high above the tank. There should be a tab on the tank to hold it in place. Mine is a 69 442. Either this or replace the cannister system.

 

That plastic piece needs to be stuffed tight with cotton ***** to act as a filter and limit the airflow in and out.

 

Thank you all guys. The fuel leaked from the left vent( i think the clamp was not tightened enough) flow down to the sharp edge from the tank what suggested me that the tank is leaking. I opened now the left vent of the standpipe and drilled a small hole in the ventil from the cap to allow air also going out, now everything is fine.
Thanks guys,this is really one of the best forums I found.

 

Hope it was just the clamp. Another source could be the sending unit on top of the tank. My car had a new tank when I got it but the gasket on the sending unit was not seated right. Gas would leak out and run to the edges by the vent lines. Is the problem worse with a full tank of gas? Check everything else first - the sending unit is easy but you have to drop the tank to get to it.