WOW, such wonderful responses and insights from so many experienced sailors! I love it. I am learning so much about my motor! Simply Awesome.
This 3GMD YANMAR (raw water) 20 HP at 3400; 1981-83 built motor was installed on the boat (newly rebuilt) in 2004. I doubt if it has more than 300 hours on it. 150 hours have been put on it over the last 14 months. One 14 day trip from sarasota to Key West and Back. And recently, the trip up to Tampa, and back 20 hours over 5 days. So, As I mentioned earlier, I discovered that there was no water thermostat. I just bought one today, and I am hoping that the motor runs right when I put it on. The impeller is new, and the old one was good. It is my back up now. I am wondering if while sitting at the Venice dock, if some plastic bag didn;t get sucked toward the intake and prevent water coming in through the thruhaul. Because, after running the motor for 22 hours on new oil and filter, she has not gotten hot, or shut down, since that time. I am sending in a oil sample for analysis, just to see if there are any major issues that are derived.
Thanks to all for your wonderful help. I will keep you posted on how it goes.
(Oh, I checked the raw water strainer, and it flushed water out when I opened the thru haul seacock, so I am getting plenty of flow. It was clean).