Fuel smell/small leak/pressure in tank after filling

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cofred
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Fuel smell/small leak/pressure in tank after filling

Post by cofred »

I nearly filled my M635 full with fuel this past weekend (I typically don't fill it all the way up, but I wasn't paying close enough attention), drove for about 15 miles and parked. When I came back to the car, I noticed a fuel smell especially when I opened the trunk, then small amount of fuel under just forward of the filler. I wondered about pressure build up, so I opened the cap and heard pressure escape. I drove another 5 miles, stopped for a Cars and Coffee event, no leakage and smell not as strong. 4 hours later, drove home about 20 miles, stronger smell, opened cap and heard pressure escape--no leak. I assume the leak I saw was secondary to the high pressure.

I'm going to check all the lines to the expansion tank etc, and probably replace them just because they should be, but my question is: is the vent hose just a vent hose or is there something that could become plugged or malfunction? Bad expansion tank?

Really appreciate your thoughts!
Heath
'85 M635
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Re: Fuel smell/small leak/pressure in tank after filling

Post by bpoliakoff »

Just a guess, but check the the 3 pipes coming from the tank. They have a habit of rusting out at their joints on the tank. On mine, I found that as well as a split in the seam so when over 1/2 full it would leak a little.
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Ronnie Wilson
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Re: Fuel smell/small leak/pressure in tank after filling

Post by Ronnie Wilson »

Hi,

Same situation happened to me. Found a couple of pin holes in vacuum pipes at the base of the fuel filler where it joins the tank. This is where dirt builds up coming from the rear tyre. Had my tank refurbished by a company who refurbish radiators.
Ronnie
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zinnocoupe
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Re: Fuel smell/small leak/pressure in tank after filling

Post by zinnocoupe »

Rusted vent pipes, and cracked, split vapour hoses would explain fuel smells and leaks but it wouldn't explain pressure in the tank. I'm not sure how all three vent pipes could become plugged enough that pressure would build up. The fuel filler neck, vent pipes, and vapour lines are the place to look for leaks. The vapour hoses should all be replaced with new.
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raykoke
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Re: Fuel smell/small leak/pressure in tank after filling

Post by raykoke »

I bet the vent lines near the filler neck are leaking due to the pressure.

These tanks were vented from the factory thru a line which exited... thru the trunk floor I think (check the diagrams on realoem).

That doesn't wash with EPA/DOT federalization so it's likely a carbon canister and associated plumbing including some valving was.. plumbed in. Start looking for blockages there.

Cheers,

Ray
'85 ///M635
cofred
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Re: Fuel smell/small leak/pressure in tank after filling

Post by cofred »

Thanks all for the great advice! Will start investigating!
Heath
'85 M635
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Re: Fuel smell/small leak/pressure in tank after filling

Post by songzunhuang »

cofred wrote: Wed Dec 27, 2017 10:40 pm Thanks all for the great advice! Will start investigating!
Watching this thread as I also have the same issue with fuel smells.
How do you take off the rubber guard around the fuel filler? The hoses attach below that but are very hard to get to unless you can remove the rubber guard. Do you access it from below?
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Song Huang
1984 633CSi
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raykoke
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Re: Fuel smell/small leak/pressure in tank after filling

Post by raykoke »

I'm pretty certain it's a press-fit.

Good luck,

Ray
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zinnocoupe
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Re: Fuel smell/small leak/pressure in tank after filling

Post by zinnocoupe »

Song, I have removed a few rubber cover things from fuel tank necks. The rubber was fairly hard on one and I finally just cut if off with an exacto knife. New ones are $29 I think. The other one I removed was in better shape and quite pliable. It took some twisting and pulling etc but it came off to access the 3 vent lines. It went back on but was a little worse for ware. Swearing is mandatory in this operation.
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Re: Fuel smell/small leak/pressure in tank after filling

Post by songzunhuang »

zinnocoupe wrote: Fri Feb 16, 2018 10:35 am Song, I have removed a few rubber cover things from fuel tank necks. The rubber was fairly hard on one and I finally just cut if off with an exacto knife. New ones are $29 I think. The other one I removed was in better shape and quite pliable. It took some twisting and pulling etc but it came off to access the 3 vent lines. It went back on but was a little worse for ware. Swearing is mandatory in this operation.
Alright then, another item to add to my shopping list. I definitely need to see what's up with all the fuel smells. I am hoping that it's just old hoses. It's funny how BMW OEM hoses appear to be encased in a fabric or cloth. When the fuel does leak, it soaks the cloth which probably makes the fuel smell last a lot longer than it would if it were a rubber hose alone.

On my todo list is to also replace all the hoses and the olitker(?) clamps around them.
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Song Huang
1984 633CSi
Last 7 of VIN: 6997383
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