Ever since I first bought my 84 500sel, there has been an annoying and very pungent raw fuel odor coming from the trunk. It is worst when I have just filled up the tank, and it wafts in most noticeably through the rear speaker holes in the trunk. It seems to slowly dissipate as my tank level drops, until I refill again at which point it returns with a vengeance. This smell does not make my car very pleasant to ride in, and nothing I have tried so far has worked. I have replaced the fuel cap seal as well as the filler neck seal to no avail. I am unsure of the exact origin of the odor, but I know it is worst when I have just filled up. If I park it right after I fill up for at least a half hour and return, the odor fills the entire passenger cabin and I am bombarded with the smell of gasoline as soon as I open the driver door. My gas tank holds pressure, as the cap is pushed out whenever I unscrew it and is never held in place by a vacuum. So what else is there that could be causing this annoying smell? Please help!

Has anyone else had to deal with this problem in the w126?

It seems to slowly dissipate as my tank level drops, until I refill again at which point it returns with a vengeance

It could be the tank itself that has a leak at the top and is only allowing fuel out when full. Have you visually inspected the tank for leaks?

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1989 300CE

As far as I have been able to see from the trunk, the tank has no leaks. It also holds a fair amount of pressure because the cap always pops off with a burst of air when I unscrew it, so that is why I thought that it wasn't the tank itself that had a leak. But is it possible that the leak is small enough to still hold pressure while allowing gasoline itself to escape? If so, how would I go about detecting the leak other than a mere visual inspection? If not, what are the other possibilities?

You might want to check fuel sender area for leak.

Check the state of the rubber on the gas cap. It doesn't take long before it stops sealing well. Add to that the rubber boot that goes around the filler neck being old and no longer sealing tight to the neck, and you wind up with those exact symptoms. Both my W126 cars have had it and the fix is a new filler cap and a new filler neck seal. Both are cheap.

If that's not the problem, then there may be some sort of clogged evap or return issue, but I'd check the two seals I mentioned first.

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-tp


1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition

I think I've fixed the problem! Turns out that the evap/vent tube that runs from the top of the tank to a drain line under the car was disconnected at the hose connection directly beneath the tank. The 26 year old hose was dryrotted to the point that all the gas coming down the evap tube when my tank was full just dripped onto the trunk floor beneath the tank. However, I've gotten a new fuel hose and reconnected it to the tube and so far, no more gas smell! Hopefully, this has resolved the gas smell stigma that has been associated with my car since I first got it!

Thank you. I'm experiencing similar issues.

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Steven
1989 260E (276K miles)
1995 E320 (50K miles)