Seems I buggered this part when trying to move the prefilter to a vertical position. The plastic nipple bit (A in 2nd pic) now leaks very efficiently and can turn. Did not touch the band clamp on this end of the hose, so thats not it I would think. Anyone run into this one and is it repairable....i.e. nipple fitting replaceable. Does not seem to come up on PP or that az place, probably a dealer only item.

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Bypass the fuel thermostat. You don't need it.

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He lives in the snowy north, he needs it. Pick up a used one, replace it, and be happy.

Thanks tjts1, that will get me by till I can find a used one or parts to rebuild it. Came across a thread on world of benz that indicates that.


Wel, it aint purty, but it will get me by and saved $150 for today... reused an old prefilter to close the loop on the fuel heater hoses after I got the thermostat out.

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If that's a 603 (looks like it to me) bypass the thermostat only and run your fuel through the heater all the time. The heat exchanger only gets hot when your cabin heater is ON so it'll only be heating fuel in the winter anyway. This is how mine is setup, works fine down to 20f that I experienced.

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There is a thread someplace which lists the part numbers for the o rings which need to be replaced. I did mine maybe 4 years ago when it was leaking I believe all the parts were in a kit for $8 which included a new plunger. I may have a unused kit as I tend to over purchase at these prices. Dealer price was around $325 at the time for a new unit. It sure helps up north.

Yes, I did find it for my and others future reference. For now I am just going to bypass it an go straight from prefilter to lift pump.

http://www.peachparts.com/shopforum/mercedes-parts-reference-library/235091-om601-602-603-diesel-fuel-thermostat-rebuild-parts-list.html

Just to followup and close this out, rebuild works fines for me. Since im the NE and run the heat I opted to rebuild rather than bypass it. I got the plastic nipple, o-ring and washer and done. Also a good idea to replace all the fuel hoses in the engine bay too while your at it...8 ft of 5/16 hose from local napa plus some clamps.