Have had a continuing issue on this summer's cruise with coolant loss in Sanderling's FL-135 engine. No pooling in the bilge, no growth in oil or transmission fluid, no green sheen on the water abaft the exhaust, no leaks in the coolant lines to the coolers/heat exchanger, spare heat exchanger didn't eliminate the loss. Did notice a little green in a small sump forward of the engine bilge, and a small amount of glycol water in a side bilge which I attributed to loose connections to the water heater. However, after tightening all hose clamps there was still a loss of coolant; it became progressively worse through the cruise to the point that I had to add 1/2 gallon after a 2 hour run at low rpms and several days at a dock. I was very worried that after leaving the Rideau (where we are taking out time with short daily runs) and having go make longer runs as we head from Ottawa to Montreal to Sorrels that the loss of coolant would damage the engine. So we bit the bullet and went into Aylings Boat Yard at Merrickville which had been recommended by several Canadian boaters for repairs. Their mechanic quickly eliminated any problem with exhaust and head gaskets, and eventually traced the problem to a failed temperature control valve on the Force 10 water heater which had been installed new by the PO just before we bought the boat 4 years ago. A call to the Ottawa Force 10 dealer (the company is based in British Columbia) confirmed that a replacement TCV was no longer being made (my guess is that there were too many problems with it). So the mechanic bypassed the valve and we were back on the water the next morning. Our hot water is now really HOT when underway. Lesson learned: when loosing coolant, don't overlook the water heater and check EVERYTHING with the engine running even if the engine room is 110 degrees and the space is cramped. Had I done this I would have seen the valve "peeing" coolant (that's how the much described it). Second lesson learned: Force 10 water heaters may not be your best choice when shopping for a replacement. -- Sent from my Droid2 phone with K-9 Mail. Follow our cruise at http://sanderling2011.blogspot.com/