This summer I had a totally random series of times that the engine overheated - sometimes just after long hours of satisfactory operation. I had replaced the cam last year and the impeller several times, even though it did not appear to be defective. The mixing elbow is only two years old. I finally caught up with a very good Yanmar parts distributor at Orrs/Bailey Island in Casco Bay. He cautioned me that any scratch big enough to catch a fingernail in the pump housing or pump cover could create these failures. I removed the cover, which did have some scratches inside, polished up the outside and reinstalled it inside out. End of problem. It was clear that the pump started pushing more water out the exhaust, and the problem has never returned.
