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7 Series - E38 (1995 - 2001)

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  #1  
Old 02-23-2014, 08:41 AM
Bonanzadave Bonanzadave is offline
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Fuel Tank Leak

Hello, 1995 740il

Please set me straight on this.....

Do the fuel tank bolts penetrate into the fuel tank ? Im looking at a bolt just in front of the RT side rear tire that appears to be leaking. I removed the bolt and saw it had a special washer/sleeve under the head that had remnants of a badly deteriorated rubber grommet.

Does this grommet seal fuel ? and where do you get them ?

I found a pic of a brake res grommet. The fuel tank bolt grommet must look like this.



Thanks, Dave

Last edited by Bonanzadave; 02-23-2014 at 09:02 AM.
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  #2  
Old 02-23-2014, 12:10 PM
Bonanzadave Bonanzadave is offline
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It looks like item #3. but I still cant tell if this would cause the leak.....

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  #3  
Old 02-23-2014, 03:20 PM
Flightmedic Flightmedic is offline
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That should be a mounting Grommit. (That's Wallace's Dog too....Cant help myself)
Shouldnt leak there.
Pop the seat up by lifting front edge. (Easy)
Youll see an embossed area in the sound-mat, lift that and remove the four screws and covers, look at hoses for leaks.


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  #4  
Old 02-23-2014, 03:29 PM
chrisn7 chrisn7 is offline
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If its as above,then this at seam level, which is where tanks leak - have you experienced the furl tank 'bong'?
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  #5  
Old 02-23-2014, 03:40 PM
Flightmedic Flightmedic is offline
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I just had fuel pumps out yesterday on my '95. There are rubber hoses up there. Easy to inspect and not unlikely spot. (Yes....Pumps. Mine has an odd Dual Pump kit installed. Puts two pumps parallel. Nice little vasket that holds them both attached to a dual screen. Assuming its aftermarket since doesnt look factory at "T" and has Dinan Supercharger)


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  #6  
Old 02-23-2014, 03:50 PM
Bonanzadave Bonanzadave is offline
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Thanks Mr Flightmedic. I wish you had pictures.

Mr Chisn7 Im new to BMWs and dont know what furl tank 'bong'? is. Please explain if you think it might help me out.

After I pulled the bolt to investigate I reassembled it with a generic grommet and it seems to leak worse. Im calling the dealer tomorrow to see if I can get the correct grommet. Then Ill have a look under the seat as Mr. Flightmedic suggests.
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  #7  
Old 02-23-2014, 05:00 PM
Flightmedic Flightmedic is offline
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Heres an idea...Does it leak when not running? Or only when running?


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  #8  
Old 02-23-2014, 05:11 PM
Podmore Podmore is offline
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What you are most likely seeing is the fuel seeping through the grommet from where it is leaking down on top of the tank seam. I doubt that the tank itself is leaking, more likely a perished fuel hose as others have suggested, from on top of the fuel tank.
The grommet does not seal any part of the fuel tank. The tank is held in place by the two straps (#5 above) but I am unsure of the function of the grommet and bolt.
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  #9  
Old 02-23-2014, 05:29 PM
Bonanzadave Bonanzadave is offline
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Quote:
Originally Posted by Podmore View Post
I doubt that the tank itself is leaking.
Thank you Mr Podmore. Ill look at the hoses tomorrow.


Quote:
Originally Posted by Flightmedic View Post
Heres an idea...Does it leak when not running? Or only when running?

Have not noticed how much while running but definitely a drop every 5 seconds when just parked.

Last edited by Bonanzadave; 02-23-2014 at 05:31 PM.
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  #10  
Old 02-24-2014, 05:20 AM
chrisn7 chrisn7 is offline
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The fuel tank 'bong' is a condition where the tank vent valve(s) in the engine bay allow fuel fumes to be purged from the system via the inlet manifold, controlled by the DME.

The breather line to atmosphere has a filter which was changed by BMW due to spiders taking up residence there and blocking it. Also the Charcoal cannister is considered to be a cause.

The symptom is a periodic loud thump under the rear seat, as vacuum devloped in the tank is suddenly released. It is possible for the bottom of the tank partially to collapse, so any 'bongs' need to investigated fast, as it quickly leads to seam leaks.
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  #11  
Old 02-24-2014, 10:30 AM
Bonanzadave Bonanzadave is offline
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Quote:
Originally Posted by chrisn7 View Post
The symptom is a periodic loud thump under the rear
Kinda what I thought it might be and possibly what may have happened. I may have popped the seam where that "leaky bolt" is.

Thanks for the explanation .
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  #12  
Old 03-01-2014, 04:27 PM
Bonanzadave Bonanzadave is offline
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Quote:
Originally Posted by Flightmedic View Post
Pop the seat up by lifting front edge. (Easy)
Youll see an embossed area in the sound-mat, lift that and remove the four screws and covers, look at hoses for leaks.
Did that....

Quote:
Originally Posted by Podmore View Post
I doubt that the tank itself is leaking, more likely a perished fuel hose as others have suggested, from on top of the fuel tank.
Dry as a bone. Hose and fuel module gasket are both leak free.

Any other suggestions.......
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  #13  
Old 03-01-2014, 05:39 PM
Flightmedic Flightmedic is offline
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Did you check both sides?



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  #14  
Old 03-01-2014, 06:31 PM
Bonanzadave Bonanzadave is offline
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Quote:
Originally Posted by Flightmedic View Post
Did you check both sides?
Ha! I didnt realize there was "another" side. I checked the passenger side. Ill look at the drivers side tomorrow.

Thanks.
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  #15  
Old 03-01-2014, 07:37 PM
Flightmedic Flightmedic is offline
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The fuel actually goes fwd up the rt side of the car; and after clearing the Fuel Rails goes back to Left side and is used to "Jet Transfer" fuel from Left to Right.


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  #16  
Old 03-02-2014, 07:24 AM
Bonanzadave Bonanzadave is offline
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Quote:
Originally Posted by Flightmedic View Post
The fuel actually goes fwd up the rt side of the car; and after clearing the Fuel Rails goes back to Left side and is used to "Jet Transfer" fuel from Left to Right.
Its -15F now so when it warms up to above 0 Ill give the drivers side a look.

Thanks again.
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  #17  
Old 03-02-2014, 07:54 PM
Bonanzadave Bonanzadave is offline
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Mr. Flightmedic, I pulled the drivers side cover. That one had 3 screws and a big rubber grommet. The grommet had a couple wires through it that ran into a small connector. that was attached to a plastic plug in the top of the tank.

Everything on that side looked dry as well.
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  #18  
Old 03-03-2014, 04:34 AM
chrisn7 chrisn7 is offline
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Is it possible you have a leak from the filler tube? Is the grommit area still wet? Did you notice this after filling up?
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  #19  
Old 03-03-2014, 05:52 PM
Bonanzadave Bonanzadave is offline
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Quote:
Originally Posted by chrisn7 View Post
Is it possible you have a leak from the filler tube? Is the grommit area still wet? Did you notice this after filling up?
Thats about the only thing you can really see without getting the car up in the air and it looks dry. and yes, the bolt/sleeve/grommet area still looks wet.

I guess my next step will be to get some ramps so I can get under it and give it look at. If there is nothing evident then I guess Ill drop the tank. This time Ill get some pictures to post.

Stay tuned......

Last edited by Bonanzadave; 03-03-2014 at 05:54 PM.
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  #20  
Old 03-08-2014, 10:45 AM
Bonanzadave Bonanzadave is offline
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Quote:
Originally Posted by Bonanzadave View Post
I guess my next step will be to get some ramps so I can get under it and give it look at. If there is nothing evident then I guess Ill drop the tank. This time Ill get some pictures to post
Well Im Back. Nothing new to report. Here is the pic of the bolt/sleeve/missing grommet from where the fuel is leaking. This is under the passenger (RT) side. There is the exact same bolt/sleeve/grommet on the drivers (LT) side.


I guess Im realizing (Duh !) that there are two sides to this tank. The drivers side is OK and completely dry. All the fuel is coming out from that bolt hole.

Here is the top of the tank. under the back seat (RT side). Dry as a bone.


Now here is a pic looking under that same access panel. Thats a pretty big line. Maybe 3/8"-1/2". It runs down toward where the leak is but then I loose it. Cant see where it goes. Hmmmmm. EDIT: I think that hose might be item #2 in the diagram (post #2)


I mentioned dropping the tank in my last post but now that I realize it runs across the whole back of the car I see thats a huge amount of work. The exhaust and heat shroud would have to be removed to even consider that.

Soooo........still leaking .

Last edited by Bonanzadave; 03-08-2014 at 10:55 AM.
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  #21  
Old 03-08-2014, 12:34 PM
Bonanzadave Bonanzadave is offline
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Quote:
Originally Posted by Flightmedic View Post
Heres an idea...Does it leak when not running? Or only when running?
NEW INFO: After about 2 hrs sitting it stopped dripping. I started the car and one minute later the fuel started coming down that side. At a pretty good rate. A drop every couple seconds.

?????

Is the tank pressurized, when running, and fuel is coming out a blown seam ?

Is there a fuel line, I cant see, thats leaking while the car is running ?

Last edited by Bonanzadave; 03-08-2014 at 12:41 PM.
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  #22  
Old 03-08-2014, 02:55 PM
chrisn7 chrisn7 is offline
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I suspect the answer is that rust, and you've either got a pinhole somewhere or its a seam.
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  #23  
Old 03-08-2014, 04:29 PM
Bonanzadave Bonanzadave is offline
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Quote:
Originally Posted by chrisn7 View Post
I suspect the answer is that rust, and you've either got a pinhole somewhere or its a seam.
Thanks Mr chrisn7, I believe we touched on that in post #10. I just cant see above the bottom of the tank. Tomorrow Im gonna pull the rear tire and wheel well panel to see if I can get a better angle on it.
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  #24  
Old 03-09-2014, 03:21 AM
chrisn7 chrisn7 is offline
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I'm afraid you won't see much of the tank by removing the wheel arch liner, other than the leading top corner. If you have self levelling, you either have to de pressurise and remove a connection or, preferably, make a strategic cut in the liner so it can be removed without doing so.
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  #25  
Old 03-09-2014, 08:00 AM
Bonanzadave Bonanzadave is offline
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Quote:
Originally Posted by chrisn7 View Post
I'm afraid you won't see much of the tank by removing the wheel arch liner, other than the leading top corner. If you have self levelling, you either have to de pressurise and remove a connection or, preferably, make a strategic cut in the liner so it can be removed without doing so.
Good info. Dont want to do "driveway" work if I dont have to. Im gonna go to my local U Pull junk yard and have a look. There is a 740 there. I need a power power steering line too.
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