Water circulation issue

[dotzel]

I have a 1986 40hp Johnson outboard. I recently had a new water pump and thermostat installed due to my motor horn going off. Unfortunately when I run my motor at half throttle for a minute or 2 it stills go off and the discharge water is warm. If I go full throttle the horn stops and everything is OK. Any suggestions what might be causing this

 

[dotzel]

I have a 1986 40hp Johnson outboard. I recently had a new water pump and thermostat installed due to my motor horn going off. Unfortunately when I run my motor at half throttle for a minute or 2 it stills go off and the discharge water is warm. If I go full throttle the horn stops and everything is OK. Any suggestions what might be causing this

 

[racerone]

Blown head gasket ??-----How much $$$ did you have to pay for the service?----Does the shop ignore you now ?

 

[dotzel]

Blown head gasket ??-----How much $$$ did you have to pay for the service?----Does the shop ignore you now ?

I did the repairs myself. I did replace the head gasket with a new one when I replaced the thermostat. Could it be the pressure relief valve by the thermostat