Ok, I know most of you guys are power boaters and all, but I have a story for a sailboat, with a new Yanmar engine. The sailboat is a brand new 52’ that was launched this summer in May. It has a gori prop, in addition to aqua-drive coupling, top of the line custom boat. On the first real shake down cruise it went from Bar Harbor, Maine to CT; over 24 hours at our speed. Due to the conditions, and timing to get to the mouth of the Cape Cod cannel we motored through the night. Running at about 3000RPM due to the weather (head wind with 8-10 foot seas, with 15 degrees off the wind), tec said cruising was 3800RPM, but 3150 to 3350 is where the boat is comfortable at. Made it past the cannel, and had some good weather in the bay, so we sailed for about two and a half hours. Then it came time to anchor for the night, so we put the sails down, and had the engine going towards the mooring field. In a matter of five minutes the engine overheat warning siren came on. After removing the cushions and cover for the engine, and checking all of the fluid levels. The only thing that we noticed is that the expansion tank was overflowing, but the main engine level was only about a pint low. Fine, we thought that most of the fluid loss was due to the overheating. We were able to make it to safety at only 2.8 kts, or else the engine would overheat. Once at the anchorage we further checked out the engine. Next morning we topped up the coolant, and finished the trip, about 5 hours, no problem. Since we where on warrantee we contacted the builder and what we get is nothing. There are no visible leaks of coolant in the engine, compartment or the bilge. So I top up coolant before the boat goes out each time. **Summer goes by Taking the boat back to Maine, same trip, with a crew of two, no problems. We stopped for lunch with no engine to let it cool then check the fluid level; no loss. Anyways this is taking a long time to explain. Finished the summer in Maine, with light to moderate use. Had the scheduled maintenance when we got back, mechanics found nothing wrong. One guy said something about the fact of the gori prop, and its overdrive feature. If it is not fully disengaged it will burn coolant during long trips, in the wrong sea conditions. That is were we left the problem, until decommissioning. Upon decommissioning the boat for the winter, it was found that our brand new engine had a very small crack in the water pump. That was the source or partial source of our problem. The gori overdrive for long distances may have been another, to bad the manual on the gori prop never got on the boat. But it’s there now! Yanmar turbo diesel less then 200 hours approx 183 hours I want to say 165hp?? My question is: Is there anything that could have been done to find the real problem sooner. I personally spent hours with a flashlight between my teeth, and a mirror trying to find evidence of a leak or something else. I saw nothing. Yes a pressure test was done, no loss. Just thought it would be a great tec, question to start a tread.