A new raw water impeller arrived for the Starwind last week. I installed it Sunday morning with the hope it would solve our cooling problem. I was a bit annoyed that the new impeller didn't come with a paper gasket, but thankfully we had a couple sheets of construction paper left in the galley cabinets after the last gasket making incident.
The new impeller worked great. Everything seemed good. I had great waterflow. Running at full throttle in the slip, I couldn't get the boat over 175 degrees. We decided to take a test run, so I put the aft berth back together and secured everything.
As soon as we pulled out of the slip, the water flow in the exhaust completely disappeared. We were blowing white smoke/steam before we got out of the marina. I turned it around and put her back in the slip.
I checked the strainer and found a fish flopping around in the catch basket. It was a tiny fish, though, so that didn't explain the sudden loss of water flow.
I had to take a break to let the heat exchanger cool down and to ponder my next move.
After two weekends of troubleshooting, the only thing I hadn't checked was the heat exchanger tubes, which I'd just cleaned last February. I set about pulling it apart. Fortunately or unfortunately, it was still clean as a whistle. There was no solution found.
My latest theory is that there's some sort of a big flap of algae and barnacle growth over the raw water inlet. When I'm sitting at the dock, water flows fine. When I move, it flips the flap of algae up over the inlet and chokes off all my raw water flow.
I've got the heat exchanger at home for a scrubbing and reassembly and a diver stopping by to scrub the hull. Hopefully this will be resolved by next weekend.