2000 2400 w/5.0l overheating

[DaveHume]

I was just able to get my 2400 on the water for the first time. It's been dry for over 12 years as I understand.
I seem to have an issue with water temperature rising at 4000 to 4800 RPM (WOT)
It has an Orca closed system and all is full. I noticed that the overflow bottle did loose about 90% due to higher heat. Temp runs about 175 in driveway testing but jumping to 225+ under higher loads. Back off throttle and things cool down. We ran at 3200 for about 45 minutes and temperature was around 200.

Thought is to replace cooling system cap, new 160 degree thermostat, and flush the closed system. I don't have any information on the Orca system and not sure how to proceed. And I don't currently have the system part number with me.

[mmwjr]

Being that the boat sat for such a long time the raw water pump impeller needs to be replaced!

[DaveHume]

I forgot to mention that I did replace the pump and housing. I did notice that there is a small piece of the lower housing that looks like a small dam that was broken. Probably less than 1/4" thick just below the pump plate.

[mmwjr]

Originally Posted by DaveHume

I forgot to mention that I did replace the pump and housing. I did notice that there is a small piece of the lower housing that looks like a small dam that was broken. Probably less than 1/4" thick just below the pump plate.

That’s a block off plate from the exhaust passage. I would do a flow test of the raw water to the heat exchanger to be sure it’s getting the correct flow per the Mercruiser manual that can be found under Documents. I find an IR temperature gun very helpful in locating where the temperature is at different parts of the system. A broken off flapper valve in the exhaust can restrict flow. When the engine is run with the cap off the heat exchanger can you see coolant flow? Remove the cap before it gets hot! This will tell you if the thermostat is open and the circulation pump is working.