The fuel filter on this engine has a thumbwheel-port on its top, in the center. It is part of the water sensor assembly that attaches to the top of the fuel filter. Its called: Protective Cap - Mercedes-Benz (000-997-63-20)

In the center of the water sensor protective cap there is a fitting to temporarily attach a drain line hose to an overflow bottle, so you can open the wheel a turn or two, cycle the key to get the fuel tank pump running, and any water in the fuel filter will be removed. DOES ANYONE KNOW THE SIZE OF THE TUBING THAT FITS ON TO IT??

Today it was -10F here in Idaho and the engine would not start due to gelled fuel. I put Diesel Kleen 911 in the fuel tank this evening to reverse the gel. I need to get that treated fuel through the fuel lines and fill the old fuel filter with it, to have any hope of starting the engine in the morning.

Opening that purge valve seems like the way to go. The water sensor has an internal tube that goes to the bottom of the filter, so any water in there can be removed. I need to put a drain line and overflow bottle on it, because I need to purge out about a quart of gelled fuel to get treated fuel into the filter.

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1st MBz: 1982 300SD
2nd MBz: 1987 300SDL
3rd MBz: 1995 S420
4th MBz: 1987 190DT
5th MBz: 1984 300SD w/1983 300DT engine
6th MBz: 1999 C230k I'm 3rd owner, got it w/57,235 miles.
and manages Mom's 2007 R320 CDI