Ok, so for the past 2 years, when i pull the boat out of winter storage it runs hot, like 180-190 underway, rising if you really open it up, be careful or you're going to overheat it hot. Impeller is recent and fine, old impeller wasn't missing any chunks. Thermostat is new too. Last year I backflushed the whole system several times, and just by some miracle the overheating issue went away after like the 3rd backflush. But it was a lot of dicking around and no obvious answer. The other thing I've tried is running without the thermostat in place at all. If I do that, the boat runs right around 140 rock steady.

So, I have a couple of questions: is it bad to run with no thermostat? Aside from taking a little longer to warm up?
Could it be that my water pump is on the way out, and with the thermostat out the impeller has enough juice to make up for the dying water pump? (the pump pulley doesn't rattle or have excessive play).
What else should I be looking at/for? I've flushed the headers, the transmission cooler, the hoses, etc. Found a lot of scale in the headers, but nothing else...

Otherwise, and with the thermostat out, the boat runs like a champ