HISTORY:

Got the boat with a bad impellor and a non functioning temp guage.
When I replaced the impeller it was missing fins. I took apart the thermostat housing and there was nothing in there. I found one fin in the water pump housing. Mechanic indicated that if I didn't find anything in either of these locations it had probably blown out the exhaust.

Installed thermostat upside down when I put it back together and overheated (cut off the motor to check it and heard water boiling) but no bad smells or performance issues.

Fixed the temp guage (loose connection)

Took the boat out and it runs right around 175-180 until I stop it. When its not running for a while and I go to start it up it will be over 200 until I run it for a minute and it will cool down. When I hit the throttle it goes down around 150 and slowly starts climbing. Ran the boat through a tank of gas like this (trying not to let it sit and goosing it a little when started to get the water flowing). My "mechanic" was supposed to go through it a month ago and has given me some bum advice in the past. I called him about the temp issue and he suggested a bad water pump housing. Is this kind of behavior normal or will it harm the boat? What should I start doing to make sure that my cooling system is unrestricted and working properly? Where should I check for blockages? If it involves going into the motor thats over my head, but if I can do it by pulling lines and checking around I feel comfortable with that. Boat runs excellent. Steams a very small amount after sitting and then taking off. No funny smells, No performance issues.

Thanks in advance