72 merc inline 6 165 overheat over 2800 rpm

[benlange]

My merc is overheating over 2800 rpm. new stat, new water shutter, new pump. Any ideas?

 

[benlange]

Re: 72 merc inline 6 165 overheat over 2800 rpm

Yes, I have a good flow of water. Just replaced the raw water pump. New thermostat. Checked function of motor water pump and it is good.

 

[benlange]

Re: 72 merc inline 6 165 overheat over 2800 rpm

Should I try running without a thermostat? It overheats within 10 seconds of running 2800 or higher, then drops to 125 - 145 when brought below 2800 within a minute or so.

 

[gadget73]

Re: 72 merc inline 6 165 overheat over 2800 rpm

I wonder if its not clogged up exhaust manifolds, restricting the overall flow of water through the engine. Do your manifolds get hot even when the engine temp is normal?

 

[benlange]

Re: 72 merc inline 6 165 overheat over 2800 rpm

I can touch them, so they are not HOT, but very warm yes.