I noticed my 1996 E300D had some leak from the Fuel thermostat (also called Heat exchanger) area about two months. I wasn't sure if it was engine coolant or fuel. My wife told me it smell more like diesel fuel.

Then, winter came. In this part of the Northeast, there are day we got 17 degree F. Starting the engine was a pain for this car while I didn't have any problem with my 2003 Jetta at all. I had to re-charged the battery numerous time after exhausting from cranking. I noticed the fuel in the clear plastic tube from the fuel thermostat to the pre-filter is almost empty when I started to crank the engine. I suspected fuel pump from the fuel tank to the thermostat must be bad or some air leak at the fuel thermostat area.

I finally decided to take action. Got the price for the fuel thermostat and gasket. Local dealer had both. I decided to start with the gasket ($6). Took the intake manifold out. Upon inspection, I realized the rubber fuel line to the fuel thermostat was cracked. It was cracked badly where it was clambed to the fuel thermostat.

To make the story short, I cut about 3/4" of the rubber hose out and replaced the fuel themostat gasket. Put everything back.

Bingo! No more leak. Fuel in clear plastic to pre-filter almost full. Engine start at 23F. I solved the problem of FUEL LEAK AT FUEL THERMOSTAT AND COLD HARD START.

Hope the community can benefit from my experience.

Glad you resolved the problem.

For reference, the thermo to prefilter line does normally drain back approx 1" at shutdown.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)