high speed overheating

[eba1225]

I have seen the other posts on low speed overheating but am experiencing the opposite. I have replaced the water pump once already.
The new pump as with the old have never run without water. What I am experiencing is that running at more than ~2200 rpm (on plane) the engine temp rises, when I come back to 1000 - 1500rpm (off plane) the temp comes back to the expected range of 150-160.

When running water to the runnig engine with the mufflers the temperature seems to remain within the desired range.
When running water to the stopped engine the flow of water seems to be full as expected.

Any insights/thoughts?

[bones484]

high speed overheating

I Have Had Some Experience With This Problem On Both V6 And V8 Mercruisers And The Problem Is Often In The Thermostat Housing. The Thermostat Itself Can Be Quite Ok But If There Is Corrosion In The Thermo Housing Then Cooling Water Can Bypass The Correct Route And Not Pass Thru The Block As Its Supposed To. Replace The Housing And This Usually Fixes The Problem Provided Everything Else Is In Good Shape I.e. Circulating Waterpump , Exhaust Manifolds And Risers Also Must Be Clear And Not Restricted In Any Way. All Of The Above Is Assuming That Yours Is Raw Water Cooled, Not Heat Exchanged.
Hope This Helps
Tony

[eba1225]

Hey bones thanks for the info.
Unfortunately the engine as well as the thermostat and housing are new.
But along those lines I was going to try to experiment with running without the thermostat and see what happens. If there is no benefit with that configuration I have to believe that it is the pump in the drive, the second one in less than three hours.