After a few days of high temps and humidity, I finally got back out to the boat today to check things out. With my head held down in shame, I'm reporting back to share that it was indeed the main raw water line valve in the closed position. The valve had been closed by the tech who winterized the boat at the end of last year. This is the first time they've done that in the six seasons we've had it winterized by this shop.

Originally, I confused the raw water thru-hull inlet for the ballast inlet, which was in the open position. When I went out today to check, I remembered what you all had said about the raw water inlet going directly to the v-drive and when I reached in through the hatch, and felt that the handle was perpendicular to the hose, unlike the others, I knew right then it was closed. I emailed the shop on Monday and they too confirmed that their tech remembers closing it - I didn't trust his account because he mentioned the valve was near the front of the boat which made no sense to me.

Anyway, mystery solved. Makes perfect sense now. Definitely odd for the raw water inlet to have clogged within minutes of running after it had been winterized.

I replaced the impeller and seal with a new one - so at least that's done.

On the bright side, thanks to you all, I learned a bit more about the water system. I learned how to swap the impeller which I hadn't done yet.

Engine sounds and runs smoothly. Hoping for no lasting damage due to overheating.

Thanks for the help.