CLK gas tank
 

This is the second time in a month that this has happened....My fuel gauge reads low fuel...I've driven 280 miles and when I go to fill up I only can put in 8 gallons and the fuel pump lever clicks off...like if the tank was actually full. I then try to put more in but the tank seems full. The fuel gauge says there is only 1/2 of a tank and 8 gallons is 1/2 of what I usually put in it....So, is there an air pocket in the tank or a plugged vent line that would cause this???

Try putting the nozzle only part way in when you fill up?

Well it fills 7-8 gallons then acts like its full....I fill it up the same way at the same gas station every time....

CLK430 fule consumption
 

The tank certainly is not full. 280 miles on 8 gallons would be 35mpg which is how-you-say-in-your-language impossible.

Fuel tank senders have been a problem for some time now and in fact a friend's '99 CLK430's sender failed in the car's first year. My W203's senders were replaced early in the game also.

The senders are on the tops of the tanks. Fold up the rear cushion, lift off the carpet and there it is. Takes a special tool to unscrew it from the tank, unfortunately.

CLK fuel senders
 

I forgot to mention that when the sender is sending bad information, the trip computer's mileage numbers are wrong also so you must fill up by miles driven until you solve this problem. Or when you run out.

There's a flap at the bottom of the filler neck (inside the tank) that opens during re-fueling. I've seen them fail, causing the problem you describe. If this is the case, the tank needs to be replaced. Some 202's (similar set-up as 208) also had problems with the expansion tank located next to the filler neck which caused the same problem.