In answer to the last post, the impellor is brand new, never been run dry or attached to a hose and I
checked it before I changed the thermostat and it was fine.

I just installed the 143 degree thermostat today and it has helped reduce the operating temps to between
140-160 depending on what I'm doing with the boat. At this point I'd say problem solved, but for the
fluctuation of 20 degrees, which I never noticed before. Is it normal to have some movement up and
down depending on speed, load etc.?

... And new problem today after I took two massive waves over the bow, the boat ran fine and the bilge pump emptied the water out quickly, but when I went to start it after sitting on the lift draining for a few minutes, it wouldn't start. Specifically, the blower was running but the starter didn't even make a clicking sound. Pure silence when you turn the key (except blower running).

I'll start a new post for this issue, but obviously something got wet that didn't like it. Any ideas?