Hi, Have noticed I have been losing a small amount of coolant from the header tank over a period of a couple of weeks, on my 2006 2.9 crdi Sedona TS. Not a great amount but you dont have to lose a lot before your heater stops working on this engine. Checked all usual connections, hoses, etc but could not find any signs of a leak. Checked oil to make sure water was not getting into the oil(head gasket problem) but nothing found. While checking the small radiator cap fitted at the back of the engine I found that the sharp edge left on the casting that the cap fastens on to had cleanly sliced through the rubber sealing washer, preventing a seal and was obviously losing fluid (although no signs of leak) probably in the form of steam. Replaced the sealing washer, and removed the sharp edges from the neck of the casting and been ok since.Simple repair but worth having a luck at if you have a similar problem.