Expansion tank vent hose routing

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Todds Coupe

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Hey guys, My 1971 coupe has a gas smell that I cannot find. It is NOT coming from the engine compartment. I recently replaced both accelerator pumps on my 32/36's. It is somewhere between the trunk and the engine compartment. The smell is not overwhelming but definitely there. Can anyone share experience regarding tracing, removing and (hopefully not) replacing the braided rubber hose between the expansion tank and the engine compartment. I have not removed the expansion tank yet as I am looking for some insight about it before I tear into it. The smell seems to be strongest in the trunk, but I can smell it when driving as well. All insight is welcome.
 
I think this will be looked at in retrospect has been one of the dumbest ideas that BMW ever had - running a gasoline vent hose through the interior of a car.
Only in the US was it done as far as I know in Europe, they wouldn’t have stood for it.
If you follow that bluish colored plastic hose running through the interior of your car from the trunk, under the carpeting , over by the glove box through the firewall across the firewall down the fender and under the battery tray, you can imagine how many places there are where trouble could step in.
Why not fix all of these potential issues by reverting your system to the European version? Just buy the inexpensive rubber grommet and use the same plastic tubing and convert your car to one that vents the gas tank through the bottom of the car at the rear.
 

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This sounds like a GREAT option. In the diagram, are you referring to part #'s 3,5 and 6? There is no identifier for these part numbers? Would I then just run a simple vent line out the bottom of the car (below the trunk)? Or, would you run it out through the filler area next to the filler pipe? And yes, I agree, running a vent line through the car seems like a pretty dumb idea. My line runs directly from the expansion tank through the car to the air inlet, under the air filters, there is no carbon filter in my coupe (1971 #2270553).
 
I think Don forgot to add that the original idea was to allow the U.S cars to go from getting 14 miles to a gallon to 14.000001 miles to a gallon!

Here is the diagram with the part number for #3. You car probably has a small hole in the trunk, around the midline, near the trunk lock, #3 was placed in from below and the line from the filler neck nipple ran to this on the Euro versions. https://www.realoem.com/bmw/enUS/showparts?id=7031-EUR-04-1974-E9-BMW-30CSi&diagId=16_0394
 
I did this modification, it is on the easy side. I found the hole already in place with a rubber plug in place. re-routed the blue pipe from the fuel tank fill tube and never gave it another thought!

While you are in there it is a good time to refresh the rubber fuel hoses around the gas tank and check to make sure no fuel or vapor leaking from the o-ring on the fuel sender.
 
100% agree with @boonies on this. i bought the drain vent from W+N when i was ordering other things - $5 in round numbers. cut the blue hose to the right length and stuck it into the vent piece sticking through the hole in the floor (under the taillight). i also replaced all fuel lines and the big hose between the gas tank and the fuel filler.
 
I too have my lines running all the way from the back of the car to the front of the car with a carbon catch can and expansion tank. Looks like someone had plugged up my grommet hole and done all of this extra work when the brought the car from Switzerland to the US. I guess I'll put it back to Euro-spec. Of course another thing I need to order from W&N, will add it onto the list for the future - part # 16121101014 is the grommet.
 
Todds Coupe said:
OK! I'll dig into it. Any suggestions for where I can get the right fuel pump? It's 45 years old, should probably replace it while I am digging around.
Click to expand...
Here is the rebuild kit for the Pierburg fuel pump. Screen shot taken by member Dic, from a Simon Fordman video also posted here, showing him getting his Coupe ready to be a driver. Video is excellent, but this photo of the actual kit that can rebuild an original fuel pump, surprised many of us. I have one now. Available from places that supply parts for old VW Beetles. Good luck!
Screenshot 2026-09-12 at 4.38.59 PM.png
 
oh, one other thing, the expansion tank disappeared from my car at the paint shop. i have 2 extras is somebody needs / wants one ... but it will remain missing on my coupe.
 
Well, I pulled it all apart and removed the expansion tank. The bottom nipple was basically reduced to fiber. I re-routed the hard blue line to a hole in the rear of the trunk to the outside. All hoses and clamps look, and smell, good, but If I can find some fuel line I will replace them as well. Additionally, perhaps I should replace the fuel pump and send unit. The pump and send unit are from 1983. Thoughts?
 
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