Is the smell inside the car , or outside ?
You could have a leak with a seal or hose at the tank ,,or you could have a problem with the Evaporative Emissions Control System , which is supposed to capture vapors and store them in the EVAP Cannister until they can be consumed by the engine when driving.
Do you have a check engine light ? Any codes ?
Otherwise you will have to inspect all the fuel system hoses etc ,,under the car and under the rear seats.

 

I also have the same problem. Fuel smell outside the car, when tank is filled. Smell goes away as soon as some of the gas is used.
Someone here recommended to change the fuel pump seal, and I did. Like the factory seal was so shallow and didnt seal well. Shop confirmed that factory seal was not sealing well.
Aftermarket/new design seal goes in much deeper, as depicted on this pic left new seal, right old seal.
Anyhow, in my case that did not get rid of the gas smell when the tank is full.

 

Check to see if the top of the sender is oily looking. If so, the plastic on it may be cracked and leaking, so the whole sender unit will need to be replaced.

 

What is the top of sender? I did try to figure out where the smell is mostly coming from and it smelled like it was coming most from the back-left of the vehicle right behind the back-left wheel.

 

Yes, that's where the sender is located. Remove the rear seat cushions and you'll see access panels and the sender (left side) and fuel pump (right side) are under there. Below is an example of a sender where the plastic housing is leaking.

 

100% exactly what my 05 clk500 had I replaced the filter/sending unit

 

The leak actually comes from the fuel tank pressure sensor, which is the black connector at 10-11 o'clock. It is not available separately from MBZ, but I have heard that some aftermarket companies now sell that. I am not sure how to replace it, though. It would be much easier than replacing the entire sender because often, the connection of the fuel lines where they attach to the pump (on the driver's side) are brittle and the nipples on the pump crack and break, meaning you really need to be prepared to replace both the pump and sender.

 

my sending/filter plastic housing was leaking and not the actual sensor right where that little ledge in the picture juts out

 

OK, I've seen that, too. I know on the W204 C-Class, that was its problem (the whole plastic housing - not just the pressure sensor).

 

YES! Gasoline fumes are EXPLOSVE!

 

When I fill up my car, once the pump stops on its own, I try to squeeze in a bit more gasoline, with a few short shots, to get the price at an even dollar. Could this be causing damage to my sender or something else that causes the strong gasoline smell to happen? Is it being overfilled?

 

No. It is either a bad seal on the sender and/or pump units, or a bad seal on the pressure sensor.

 

I had the fuel smell also;; it was the sender/filter on drivers side; the plastic shell had a crack in it I replaced it and the fuel pump also if u go with after market sender/filter like I did U have to change the fuel pump as the lines are different and its almost impossible to get the fuel line off the factory pump etc also the fuel sensor requires a MB wiring adapter as the sensors are different on the plug in end from the oem to replacement one Mercedes part# 211 440 05 07 are 18$ on amazon

 

The leaks were coming through the center ,the puddle was on the sender and collected in depression on tank ,the gree show the access to retaing clamp not sure how to loosen that ??

 

yes exactly the same as mine you have to replace sender assembly

 

Welcome to the forum @Scotslad2k - please take a moment to read the information on the link below. It explains how to update your user profile so that your car's details and your location appear on each post below your avatar. This is good information for others to know when trying to help. It also has good information about how the forums are organized and how to use the search feature:

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If yours has the same worm-gear screw clamp as shown in my photo, then you have the "California emissions" version. You just need a suitable angled nut driver to rotate the bolt. If you do not have the California emissions version, then you use a large "clamp wrench" to unscrew the plastic retainer retainer ring - much like changing a camper or under-sing water filter.

 

I can't believe this gas puddle static leak issue is not on NHTSA radar , talk about a fire hazard.

 

If you overfill the tank, it is possible that fuel can get into the vent tube that leads to the charcoal canister. It's very rare, and you'd really have to force it and have fuel spilling out of the filler to do this. With the "saddle" style tanks, I've found that giving the car a bump or two with my hip will burp a bit of air out and let me pump in another 0.5-1.0 gallons.

 

This is a defective plastic housing I can soak up the gas and then just watch as it seems back out through these micro cracks till it puddles up again,gas tank is only 1/2 full at the moment.still leaking