Have a 170 closed system with 3 inch exchanger, used in fresh water only. drive is new as of last year, motor pump is good. When running slow the temp climbs up close to 200. Loaned the boat to a friend today & he putted around for 20 minutes, noticed the temp was high and shut it off, then headed back after it cooled down. He also said there was a lot of water in the bilge, pumped it out & by the time they got back there was a lot more water in the bilge. I hooked up the ear muffs at home tonight & let it idle for 20 minutes and it stayed at 150 also there was NO water leaking anywhere. The water issue may be a leaking plug. Anyway there is probably rust flake clogging things up. Should I remove the heat exchanger & the riser above the exhaust manifold? is there anything I can check?<br />p.s. had it out 3 weeks ago and ran it fairly hard & it was fine.