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chuck21401 · Joined: 20 Feb 2005 Posts: 526 Location: Annapolis, MD

I went to get gas the other night. After adding about 6 gallons I noticed fuel leaking under the car. Looking underneath it appeared to be come from the top of the tank/fuel filler area. I let the fuel evaporate and drove home.

Ran some searches on 924board. Suspects include the hose between the fuel filler and the tank, the vent line and possibly a cracked tank (but hopefully not!).

I opened up the filler neck area. The cloth covered vent line was soaked with fuel; the other lines seemed fine. The larger rubber hose from the filler to the tank was tight and not soaked with fuel.

Returning to the vent line....duct tape. That's not a good sign. I'm guessing there is a crack under there?

From what I've read, the only way to replace the tank vent line is to drop the transaxle and fuel tank. Is that right?

But I don't understand why the vent line would leak upon fill up. Is there enough pressure to push the fuel up the vent line?

Here are some pics. Anything look unusual?

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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler

MikeJinCO · Posted: Tue May 11, 2021 2:23 am Post subject:

Having had a cracked tank. I'd leave the cover off and put more gas in while watching. I don't understand that wet hose as that should be unrelated to a crack in tank. That vent line goes back down and vents in the rear corner. You can loosen the holding straps and drop the tank an inch or two to see what is going on better.

Removing and repairing a tank is such a pain to do, lots of investigation is worth doing first. If has the Audi 5 speed gearbox, it in itself is nasty to get out.
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Mike

'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11723 Location: PacNW

The stampings in the top of the tank may have cracked from years of flexing.

Well documented at Pelican, here:

http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/251194-gas-fumes-tank-leaks-read.html
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

chuck21401 · Joined: 20 Feb 2005 Posts: 526 Location: Annapolis, MD

Thanks for the link on Pelican. Hopefully that is not the problem here.

I pulled off the duct tape. Sure enough the line is weakened exactly where the metal line inside it ends. Below you can see how the line is frayed and most likely cracked underneath. Still not sure how such a volume of fuel would leak out there...the fuel would have to find it's way all the way up the vent line, right?

Will continue to investigate. Will add some fuel from a gas can to see what happens.

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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler

Fifty50Plus · Posted: Tue May 11, 2021 4:34 am Post subject:

Probably leaked when you filled the tank and the overflow tube and hose got some fuel in it.
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1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car

chuck21401 · Joined: 20 Feb 2005 Posts: 526 Location: Annapolis, MD

Added more gas to the car from a gas can. I pushed a paper towel down between the tank and the larger filler hose. As I was watching, I could see a small amount gas at the base, circled below. When I pulled up the paper towel it was wet with gas.

I checked the hose clamps on the big hose, they were tight. I thought maybe I could reseat everything and try again. As I loosened the hose clamps to do that I realized that two gaskets shown on the parts diagram on either side of the large filler hose are missing, Part #10 below.

944 201 217 00 is NLA but looks like 944 201 217 01 is available from the usual sources. The large hose is probably due to be replaced after 40 years but appears to be NLA. (Bellows - 477 201 357).

This is part 944 201 217 01

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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler

chuck21401 · Joined: 20 Feb 2005 Posts: 526 Location: Annapolis, MD

chuck21401 · Joined: 20 Feb 2005 Posts: 526 Location: Annapolis, MD

!tom · Posted: Thu May 13, 2021 3:12 pm Post subject:

I had problems with leaks from my gas tank too. You can read about my saga
here.

Sorry the pictures are gone, but the gist of the story is that the tank would hold a vacuum, but would not hold pressure, due to a failed gasket on the fuel sender. I replaced the gasket and all the issues were resolved.[/url]
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78 924 NA
5-lug

chuck21401 · Joined: 20 Feb 2005 Posts: 526 Location: Annapolis, MD

Eliza · Posted: Fri Sep 03, 2021 2:58 pm Post subject:

Hello Chuck,

bit late, but for what it's worth...

since I bought my 931 RoW 1981 and couldn't stop wondering why I seem to constantly overfill the fuel tank ( on my 1985 RoW 924 I never had this problem ) I ripped my filler neck and hoses apart to see what goes on there.

I noticed the filler neck itself on the 1981 car to be fully unrestricted, just an almost 5 cm diameter aluminium pipe. The 1985 filler neck has a restriction in the lower end, probably owing to the introduction of unleaded fuel somewhere in 1982 and the consecutive intruduction of smaller fuel nozzles at fuel stations...

Anyway, the larger filler neck on the older car will only get the pump nozzle to click off when the filler neck itself is already full, meaning fuel will sit in the filler neck and the rubber boot to the tank. So your 15mm vent hose would then also be fuel filled up to that point, and if it does have a crack, it would explain that it sweats fuel.

I was already wondering, am I imagining this? Why has nobody else with a pre-1982 car mentioned this overfilling thing ( for as far as I can find anyway )? I think I'll swap to the later filler neck SOON.

Just to confirm, the new gasket 944 201 217 01 fits the bellows in my car. And the bellows from A VW T3 will fit, otherwise Rosepassion has a replacement for 477 201 357 that fits, just needs shortening to 135mm.

Eliza
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1985 924 NA RoW
1981 931 S2 RoW

chuck21401 · Joined: 20 Feb 2005 Posts: 526 Location: Annapolis, MD

Eliza · Posted: Sun Sep 05, 2021 5:06 pm Post subject:

I'd love to drop the tank also, and replace the hoses just because... especially as I am told the gearbox/transaxle on my car need not be dropped to get the fuel tank out.

I'll speak to my trusted mechanic next Wednesday. If possible, even dropping the tank a little bit, rather than taking it out completely, might let me get at the hoses... who knows. If you want, I'll let you know if I learn anything useful.

Good for you to find at least a temporary fix! This fuel smell is disquieting. I keep seeing before my inner eye all sorts of doom scenarios

Eliza
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1985 924 NA RoW
1981 931 S2 RoW

chuck21401 · Joined: 20 Feb 2005 Posts: 526 Location: Annapolis, MD

Eliza · Posted: Thu Sep 09, 2021 3:03 pm Post subject:

Hi Chuck,

the promised feedback. NOT promising. I had hoped that the tank might be lowered a few centimetres on the front.. no way do I think that'll be possible. First of all it looks a really tight squeeze up there, and secondly, taking a look at the top of the tank with it just lowered would still be impossible owing to the sheet metal forming the rear seat hollows ( slanting downwards right in front of the front end of the tank if that makes sense). I'm afraid dropping it completely is really the only way to go.

Bummer. I put it on the to do list as well. For now, I swapped the filler according to TSB 20-82.01 against the newer version with a float and replaced all hoses I could get at - unfortunately, now the white plastic cover no longer fits over all the new bulk

. I'll have to figure something out. Hmpf, never as easy as I imagined

Still, it was a good idea. I asked my mechanic who drives - shall we say - a bit more aggressively than I to take the car for a spin and try to corner as fast and as hard as possible. He did. And I felt a bit dizzy afterwards, but NOT from fuel smell

.So at least I seem to have sorted things for now.

Let me know if you want pictures or anything.

Eliza
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1985 924 NA RoW
1981 931 S2 RoW