Johnson 20hp Overheating

[BlackSwam]

Hello all, new to the forum here. Im having some trouble that I hope someone here can add some info.


I have a 1998 Johnson 20hp and I am having issue with it overheating and cant seem to find the problem. I can take my boat out and can run it for around 5-10 minutes fine. After that the motor starts to stutter whenever I get past 30%-40% throttle, as if its getting and cutting the power very quickly. I narrowed down the problem by cutting the wire to the overheating sensor which resulted it in running normal (I only ran it 20-30 seconds just to verify the problem). The tell tale is flowing normal and since then I have removed the head and exhaust covers and cant find anythings that would be blocking the flow of water. It has a new impeller, water pump, power pack, all new gaskets, stator, temp sensor, thermostat (tested since and works). So I'm at a road block as to what could be the problem.

Also oil mix is always 50:1

Thanks in advance!

 

[johnnygjr]

check compression on cylinders to see if head gaskets were installed and torqued properly. pull plugs look for moisture.if they are very white there is water getting in!

 

[BlackSwam]

Compression was 130# and the plugs seemed normal

 

[johnnygjr]

any droplets on plugs?plugs normal you say. are they light brown fuel and oil on them? When i said droplets i mean water.You said you saw no possible blockages on head and block. try desalting engine in a barrel with proper solution.

 

[kimcrwbr1]

Was the old impeller broken up into pieces? Pull the thermostat out and start the motor water should gush out the hole.