C220 Cdi 2003 (W203) Winter's approaching and I'm not prepared to put up with the cold running of the C220 anymore, and before everyone chimes in with, "it must be the stat"; it aint. I thought it must be the stat too, so at the last service I got the garage to replace it, but it made no difference. Took it back, they scratched their heads and changed it again, but it still made no difference. I began to think that maybe the garage fouled up something when refitting it, so I got it out and tested it in a saucepan on the cooker. It opened and closed repeatedly at around the 92C mark, and sealed perfectly in the housing. I can run 50 miles up the motorway at 70mph and the temp only just manages to reach 80C after about 15 miles and that's without the cabin heater on. Also when the engine temp is at an indicated 60-70C I can feel heat in the radiator, so I've also changed the temp sender unit in case that was playing up. The stat has been tested so I know it's working correctly but the radiator is still warm long before it should be, so there's only way this can happen as I can see it, and that's by getting back flow through the fuel heater. Trouble is I can't find any information on this device, no schematics of the flow paths or any temperature controls. Does anyone have any details?? I think I might try clamping the rubber hose between the stat and the fuel heater to see if this will encourage a faster warm-up.