One other thing to check is behind the water bypass cover plate on the side. The place where the water comes in at low speed. I doubt this is related to your current temperature concerns but check it to be safe. I overheated my ’54 SuperFastwin due to the area behind that plate being clogged. It would pump lots of water standing still but starve for water when the boat was moving. I ALWAYS check behind there on new to me motors now.
-Ben
OldJohnnyRude on YouTube