Euro tank ventilation

[frederik]

After filling up (to the first click), I almost always get gas fumes in the car. These disappear after driving for about 20-30 km. After that, there seem to be no further gas fumes -- I suppose there's always a little bit in an old 911. But after filling up, it gets annoying.

I did some research and found that there is an elaborate system for US cars to ventilate the tank without exposing fumes to the atmosphere. I couldn't find much on the Euro system: it looks like it only uses the expansion chamber behind the dashboard, and then lets that vent to the outside just next to the filler pipe (together with the brake fluid overflow). Is that correct?

Anyway, my car (from the US but in many ways converted to Euro spec) has none of that. My mechanic just fitted a short hose with a one-way valve to the tank ventilation connection. He says this prevents trouble with the factory ventilation system (since it often leaks) and is perfectly fine, since it allows air in, but no air out. My feeling is that Porsche didn't install a more elaborate system for no reason. Could it be that my gas fume after filling up problem is related to this?

According to my mechanic, if the pressure in the tank needs to be vented, there is a separate vent pipe in the filler pipe. Is that true?

[edmayo]

Check your gas tank cap gasket. I have a 72 euro S for comparison but that does you no good since you have a U.S. car anyway. There is quite a bit to a U.S. car,,,,got a parts book? shows everything.

[gled49]

My Euro 73 just has the expansion tank under the cowl, and the tubing from there goes thru the front latch panel by the front spoiler. The gas smells in my car are more from lack of charcoal canister evaporative system. G

[Longballa]

I set up all the hot rods I build with the euro set up. US one is ridiculous. If the car sits in a garage or tight space you'll smell gas after awhile but you say after fill up. How old is the black box and lines? You shouldn't smell it in the car. If it's an original black box I'd replace it.

[Arne]

Scott & Ed - if I wanted to simplify my US '72 T to the euro venting, I assume that I would just cap off the nipples on the airbox and yellow air guide, and run new PVC tube as shown here.

But what connects to the unused barb on part 55?

[HarryD]

This post by Grady Clay at the Pelican Parts BBS may be helpful. forums.pelicanparts.com/porsche-911-technical-forum/584831-fuel-tank-venting-system-question.html#post5778219

Here is the 1969 Evaporative Emissions System


© 1969 Dr. Ing. h.c. F. Porsche K.G.
This shows the fuel system for the 911T (pump at rear), #2, 4, 16, 17.
and
the fuel system for MFI 911E & 911S, #3, 4, 7-10, 16-19, 37-42 and more.
(In 1970, the 911T is plumbed as the 911E&S here.)





The ‘tee’ fitting (#44 above) does not show a 3rd connection here.
My recollection is that is the small vent hose to the filler neck.

The outlet goes through a grommet (#47) in the front panel behind the windshield washer reservoir.
It vents between the front bumper and the inner panel.





System for '70-'71.

© 1970 Dr. Ing. h.c. F. Porsche K.G.


Best,
Grady

[edmayo]

Scott & Ed - if I wanted to simplify my US '72 T to the euro venting, I assume that I would just cap off the nipples on the airbox and yellow air guide, and run new PVC tube as shown here.

But what connects to the unused barb on part 55?

They just used a rubber cap to close off that barb. Also a rubber cap closed off the unused tee at the back of the aircleaner and the fan housing (air guide) There was also no steel pipe between the filler tube and the vent system, no steel pipe coming off the filler neck, and the hole in the filler well was plugged with a plastic cap.

[frederik]

Check your gas tank cap gasket. I have a 72 euro S for comparison but that does you no good since you have a U.S. car anyway. There is quite a bit to a U.S. car,,,,got a parts book? shows everything.

Thanks Ed, do you mean the rubber gasket for the filler cap? The cap with the gasket looks new to me. It does seem to me that the smell must be coming from this area since there is no smell in the trunk. Maybe it could get into the cabin via the left vent window (I have it open all the time). Is there a further venting near the filler tube? There is a hose going down behind the left front wheel, ending just above the pavement that seems to be for dumping excessive petrol. There is nothing US about my ventilation system anymore, everything has been removed.

My main question is, do you have experience with the system I described that just connects a one-way valve to the hose #49 in the diagram below? I don't have #42, the expansion chamber. I would be willing to rebuild the Euro system in this diagram if it fixes the smell and if I can find the parts.



BTW, doesn't #44 connect to the brake fluid overflow? So that is dumped on the street as well in front of the left front wheel.

[Robert5995]

Arne -

The other stub off part 44 I think is for the brake master cylinder overflow.

- Rob

[edmayo]

Only for 69, my m/cyl. Vents thru front bulkhead.