Expansion Tank filling with Fuel

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passta
Posts: 33
Joined: Wed Apr 07, 2021 12:53 am
Location: Missouri

Expansion Tank filling with Fuel

Post by passta »

I've randomly had a fuel smell in the trunk from time to time, and also, have had fuel dripping from the expansion tank mounted in the trunk under the rear shelf, the plastic tank with 3 hoses from the tank, and 1 going to the hard breather pipe out under the car. Last year was the first time I had this originally happen, I checked all the hoses and blew compressed air thru them, they all were clear but I had no idea how old they were. So I replaced all of the hoses from the 3 metal breather pipes on the fuel tank filler neck to the expansion tank, as well as the 4th hose out of the expansion tank to the hard line. The issue of actually having fuel fill up the expansion tank, was gone, since I replaced the hoses until today although occasionally I did notice a fuel smell when the tank was full but I that could have been my imagination. Today I noticed a fuel odor while driving, tank was over 3/4 full, and in the past when I had smelled this, there was almost always a vacuum on the tank, so I pulled in to a gas station, opened the filler cap on the tank, and it had a vacuum, air rushed in when I opened it. I didn't see any fuel on the expansion tank, so I drove home, less than a mile, and when I got home and opened the trunk, I could then see file dripping from the expansion tank. Took that out, drained the fuel, and blew air thru all the lines, they were all clear. I did notice some weeping on one of the hoses on the breather pipe end, but the hose itself is not cracked or split and the clamps were tight. Breather pipes are not rusted and no holes in them. I'm not sure what else could be causing this other than something in the tank itself? The gasket on the in tank pump is new and there is no leak there. Fuel lines also are new throughout the entire system.

Car is an 85 M635 Euro so not sure if there was some federalization done to it with this setup anyway?
Saint Louis, MO
90 E32 750il
85 M635CSi
15 F10 M5 (gone)
07 E60 550 (gone)
02 E39 540 Touring (gone)
87 E28 535IS (gone)
85 E23 735 5spd(gone)
85 E24 635CSI (gone)
86 E28 535IS (gone)
bpoliakoff
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Re: Expansion Tank filling with Fuel

Post by bpoliakoff »

My 81 is a Euro. If you are a non modified Euro, your tank is vented as is mine via the hard line that exits in the rear of the car, I forget exactly where. I do not believe there is a one way valve on the hard line that is the vent line. So there can not be a vacuum in your tank, unless I am missing something
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.
streifen
Posts: 10
Joined: Mon Nov 28, 2022 4:58 pm
Location: Los Angeles

Re: Expansion Tank filling with Fuel

Post by streifen »

I just stumbled on your post and hope you found a fix for your vapor system issue.
If not, check your carbon canister; remove it and check for liquid fuel. It's a pain in the rectum, but blow out the lines again. The only way you can re-use a saturated carbon canister is to purge hot nitrogen through it, but that's beyond our means.
Check to see if your intake fuel vapor scavenge valve (vacuum or 12 volt operated) is functioning as per design. (My driver is an 85 with a vacuum operated vapor scavenge valve)

Do not use braided fuel or vapor lines. They are not designed for the radical fuel mixtures we see now. Junk, junk, junk. Safety first.
I use Gates barrier hose which is a bit expensive (The best buy at Pegasus Racing).
Use clamps on all your vapor system hose connections.
On the vapor system check valve,,, I have yet to find a BMW spec check valve (pictured on OEM) that that works for more than a weeks duration. I expect that the plastic used in these check valves is also effected by the fuel additives and thus incompatible. (I find the inner check ball stuck to the housing on surgical disassembly).
A check valve designed for vertical positioning located at the vapor canister is the best. Good luck finding a compatible and durable valve that is sensitive enough to respond to vapor pressure and chemical compatibility.
Recognizing that the plastic vapor tank is, by design, akin to making a bomb, it should be on a routine inspection. I have found that during the hot summer months, I'll open the trunk and hear a high pitch whistling which is vapor pressure escaping... and tighten the clamps again.... So my cure is:
In California the extensive smog inspection includes a cursory check of the vapor system. Once the inspection is done, I install a tee with a plastic check valve in the upper, (top most) vapor vent on the fuel tank filler line. The check valve vents excessive pressure to the atmosphere and re-seats via gravity. I buy BMW valve PN is 1 707 770. Buy 4-5 at a time. 4mm barbed connections. If necessary, I use heat shrink to hold the tee pieces together. To hell with the smog requirements! Safety first.
TimU
Posts: 280
Joined: Tue Dec 14, 2021 2:16 am
Location: Sydney

Re: Expansion Tank filling with Fuel

Post by TimU »

streifen wrote: Tue Jun 13, 2023 4:34 pm I just stumbled on your post and hope you found a fix for your vapor system issue.

If not:

1) Check your carbon canister; remove it and check for liquid fuel.
It's a pain in the rectum, but blow out the lines again.
The only way you can re-use a saturated carbon canister is to purge hot nitrogen through it, but that's beyond our means.

2) Check to see if your intake fuel vapor scavenge valve (vacuum or 12 volt operated) is functioning as per design. (My driver is an 85 with a vacuum operated vapor scavenge valve)

3) Do not use braided fuel or vapor lines. They are not designed for the radical fuel mixtures we see now. Junk, junk, junk. Safety first.
I use Gates barrier hose which is a bit expensive (The best buy at Pegasus Racing).

4) Use clamps on all your vapor system hose connections.

5) On the vapor system check valve, I have yet to find a BMW spec check valve (pictured on OEM) that that works for more than a weeks duration. I expect that the plastic used in these check valves is also effected by the fuel additives and thus incompatible. (I find the inner check ball stuck to the housing on surgical disassembly).
A check valve designed for vertical positioning located at the vapor canister is the best. Good luck finding a compatible and durable valve that is sensitive enough to respond to vapor pressure and chemical compatibility.

6) Recognizing that the plastic vapor tank is, by design, akin to making a bomb, it should be on a routine inspection.
I have found that during the hot summer months, I'll open the trunk and hear a high pitch whistling which is vapor pressure escaping... and tighten the clamps again....

7) So my cure is:
In California the extensive smog inspection includes a cursory check of the vapor system.
Once the inspection is done, I install a tee with a plastic check valve in the upper, (top most) vapor vent on the fuel tank filler line.
The check valve vents excessive pressure to the atmosphere and re-seats via gravity.
I buy BMW valve PN is 1 707 770.
Buy 4-5 at a time. 4mm barbed connections.
If necessary, I use heat shrink to hold the tee pieces together.
To hell with the smog requirements! Safety first.
Thanks for your detailed list - I've just reformatted it as numbered points to aid in my own reading and responses.

Here's the RealOEM diagram to visually assist as well.
Source: https://www.realoem.com/bmw/enUS/showpa ... 1631707770
E24 635CSi Expansion Tank & Activated Carbon Container.png
E24 635CSi Expansion Tank & Activated Carbon Container.png (141.63 KiB) Viewed 543 times
.
.

Regarding your points:

Re: 3 - "Do not use braided fuel or vapor lines [...] I use Gates barrier hose"
Why would a modern fuel line not be suitable for modern fuel mixtures?

Is this the Gates hose you were suggesting?
https://www.gatesaustralia.com.au/produ ... n-hose-mpi

Re: 5 - "Good luck finding a compatible and durable valve that is sensitive enough to respond to vapor pressure and chemical compatibility."

Would something like this work?

1-Piece Stainless Steel Spring Check Valve
https://www.zetco.com.au/check-valves/1 ... p-threaded
b6d7090a321aeca0f529ab265a288b1b_S[1].jpg
b6d7090a321aeca0f529ab265a288b1b_S[1].jpg (14.62 KiB) Viewed 543 times
Re: 7 - " I install a tee with a plastic check valve in the upper, (top most) vapor vent on the fuel tank filler line."

Would you be able to show/draw/highlight exactly how and where you've installed the T-Piece & Check-Valve to please?

----
Thanks in advance.
Tim
04/1986 635csi Euro spec
Australian Delivered, RHD
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