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Gas Fumes in Trunk


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I went to extreme measures to make sure my gas tank was not leaking: I sealed it with POR 15 gas tank kit, new "O" ring on tank sender unit (properly lubed with Vaseline), all new rubber hoses, and even pressure and vacuum checked the plastic supply line and metal return line.  After running the engine for a few moments, I noticed a strong gas smell in the trunk. Dang...what did I miss??

The culprit was the small plastic sleeve under the rubber supply hose on the fuel sender.  This is needed because the fuel pickup on the sender is 6mm and the plastic supply  line is 8mm. The mechanical fuel pump sucks from the tank, and has a check valve to keep fuel between the pump and the carb. However, the fuel in the line between the tank and the pump drains back to the tank. The plastic sleeve is old and cracked (just like me) and the backwards flow of fuel (pump is higher than the tank) causes fuel to leak and collect on top of the sender unit. Solution: I slipped a small  rubber hose over the fuel pick up, and then installed  the 8mm rubber hose and secured with a hose clamp.


PS: The green wire is an extra ground wire. This cures the gas gauge from jumping when you use your right turn signal. The right tail lights and gas level sender share a common ground.



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Ya learn something new every day.  Never had that sleeve cause a leak, so never messed with it.  But I did replace that old cloth-covered fuel line many years ago--the cloth hides cracks in the underlying rubber, which will also cause a gas smell--at a minimum--and eventually a full-fledged leak.  I think I must have replaced it with US 1/4" fuel line, which corresponds with 6mm so didn't need the sleeve.




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On 4/20/2017 at 3:29 PM, halboyles said:

That plastic piece is the same ID as the hard nylon fuel line that runs to the front of the car.  You only need about 3/4" so I have often cut off a piece from the end of the nylon hose to replace that little piece on the tank outlet.  Fixes the stink from that source every time.

I followed Hal's suggestion today and just thought I would share photos. 


Thank you Hal. :)

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It simply makes it the right size to accept the hose. 

I had neglected adding the sleeve, when replacing those hoses and it leaked a bit.

My solution was to simply tighten the 5/16" hose onto the smaller nipple.

I felt guilty, so I went back today and added it.

I feel much better now.  No stink.


That fuel line really is a perfect press on fit.

I see no reason to order a special part from BMW.

Nice sharp bypass pruners do a good job of snipping it.

They work really well on hoses too.


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