I've been getting strong gasoline fume odors for a while now when filling the tank, so I replaced the seals today. It took me about 1.5 hours. The hardest part was releasing the seal ring clamps. On the older design, the seal rings unscrewed. On the new design, there is a metal "hose clamp" around the seal ring and it's a pain to access the screw. I used a combination of an offset screwdriver and a universal socket adapter.

After removing the back seat and access covers, I could easily see why I was getting the fume odors - there was a bit of standing fuel on top of the sender housing (left side of the tank). I mopped up most of the liquid before taking the photo. There were signs of some stains on the pump housing (right side), but not much. When I removed the sender, I could see a lot of staining on the seal ring. And the final photo, you can see the difference in the redesigned seals.

The job was fairly easy, but I am glad I have the cabriolet - it would be a pain to fold myself up inside the coupe. I really had no trouble. The pump on the right side is easier since there are no wiring or hoses to deal with. The electrical connectors and fuel line on the sender have to be removed. Neither the sender nor the pump have to be removed - the seal can be stretched over the top. I found it easier to seat the seal on the tank first, then push the sender and pump into the seal.


This is what the top of the sender (left side) looked like:



And this is the pump (right side):



Here's the stains on the underside of the sender's seal ring:



Finally, the new seal (on the left) vs. old (on the right):

 

Wow, that new seal looks a lot bigger. I have the same problem when I fill up. I have been stopping short of full to alleviate the smell. Might have to do that fix myself. You would think that a company like MB would be on top of a safety issue like that.

 

This may not be the problem on your MY2004. I think the pump, sender and retainer rings were redesigned and they use the same seals as the prior models, and that;s what caused the problem. The seals on the C240 have never given us a problem, but it has the older style system with an external fuel filter. My CLK has fuel filter internal to the sender unit. I think another source of fumes was the filler neck seal.

 

My car has the internal fuel filter same as yours. I also read that the top of the sender was prone to cracking. I saw a post where a guy filled the top of the sender with epoxy to fix it. Otherwise you need to buy the whole sender.

 

I didn't notice any cracks on my sender, but after filling the tank yesterday, I am still getting some fumes odors int he garage this morning. The problem is, I used some cleaner on the parts so maybe I am still smelling that. Also, I cleaned my "used oil bucket" and tossed some oily rags in the trash, so it could be that, too. Regardless, I think I might remove the seat and access panel today and re-check it.

 

Well, I checked and the top of the sender is full of gasoline. Since it's time to replace the fuel filter anyhow, I just going to order a new sender ($256!).

 

Had the same problem on my '06 Cabrio. Dealer replaced sender under my extended warranty. Gas smell gone immediately. That warranty saved my bank account on more than one occasion. Bought used a year ago and have used it on rear main seal, upper oil pan gasket, sender unit and just recently the crankshaft speed sensor. Hope things are square for a while.

 

It kinda looks like you were leaking fuel from where the fuel line attached. Did you ever get this resolved?

 

No, not resolved yet. I just never fill over 3/4 full. And its not leaking at the hose. I think there is a crack in the housing under or around one of the the electrical connectors. One of these days, I am going to remove the seat and access port and watch it as I refuel to see where it seeps in from. I remember a guy on the forum (or maybe over on benzworld) foudn his and used epoxy to fix it.