130 HP overheat problem

[jetlear]

OK, I am an aircraft mechanic. These engines have me stumped. I recently purchased a pair of engines on a Grady. 1989 130 hp CR pair. They have been great. I decided to change the impellors as a preventative maintenance issue since I did not know the vintage of the impellors. Due to time constraints and other considerations, the boat was high and dry for three weeks for maintenance. It has always been operated in salt water. Prior to the change, the engines operated perfectly. After the change one engine began to run much hotter at RPMS above 3500. I dissasembled the pump to find that a piece of brass had scored the lower pump plate and gouged the impellor. Rechanged the ENTIRE assembly and retewsted the engine. Ran warmer but not as cool as prior to the first change. Erratically the temp climbs to unacceptable levels measured on the boat in the water with infrared measuring equipment. Flow seems good, t-stats are new. Compression is perfect and plugs show good burn. Only event is the change of the pump assemblies and the 3.5 week layup. Any ideas?

By the way, the other engine runs cool as ever.

[Ken]

jetlear,
I would check the pressure relief valve on both outboards for mineral/deposit buildup or for broken spring. If the PRV sticks partially open, then the cooling water from the pump bypasses the cooling jakets and dumps out the relief holes.
Also, you say a piece of brass was found in with the impeller - could some foreign object possibly have gone up the water pump tube and may be restricting the water flow to the cooling jackets? You might want to pull the thermostats and look behind them for any blockage.
Good luck,
Ken K