overheating
 

ok I went out today and didn't get more then a mile before I heard the alarm. temp was close to 200
shut it down and checked everything.
drove it again after about 30m temp dropped to normal then back up once I got up on plane. So I shut it down and pull the return back from the oil cooler to the T stat housing fired motor and water comes flying out. At this point I know Im getting good water flow. my stainless marine manifolds were not hot since I could touch them. finally after a few calls to AudioFn I pulled the T stat
and the temp dropped, but if I idle the temp rises, On plane the temps seems good. Do I just have a bad T stat?
this is a Volvo 502 looks like a hp500 though
http://www.performanceboats.net/images/engine.jpg

my plan is to replace the T stat, flush the oil cooler and replace the impeller

I don't know if I should replace the circulatory water pump?