I just bought an '82 Catalina 27 with a 5411 diesel and am working on figuring the engine out. Luckily I don't have to worry about winterizing here in Santa Cruz. There is a valve in the return cooling line from the thermostat to the raw water intake. The valve is closed. I do get some water out the exhaust, so either there's no thermostat installed, or there's leakage around it to the exhaust. It seems like that's a bad idea to have it closed, or is there some good reason for keeping it closed?
The temperature gauge doesn't seem to work (or maybe the engine is always running cold?), which is on my list of troubleshooting projects (in addition to the wiring harness and the throttle control, topics for a new post).
Rob
Santa Cruz