Overheat Horn on a 1984 150 V6 Merc

JimDD

Cadet
Joined
Jul 28, 2009
Messages
16
I had previously demoed my oil injection system because of nuisance alarms with it. By doing this I also had demoed the overheat horn circuit which was in the wiring harness for the oil injection alarm module. I recently retired and wanted to reestablish some reliability (confidence) on the motor. Especially with the overheat alarm system.

I recently hooked up the wires from the temperature sensor to a new 12V horn using what I thought were the correct wires as indicated in my shop manual for this engine. Problem I am now encountering with this all hooked up is the horn is blowing indicating an overheat condition that I suspect may be faulty but I am not 100% sure. The horn does not blow at idle RPMs but does come on after running the engine for a short stretch putting my boat on a plane.

I do have good tell tale flow and I am indicating 15 psi of water pressure at 2500-3000 RPMs. I recently replaced the water pressure gauge to see if this may have not been indicating low pressure but that was not the case.

Is there anything that could be wrong in the powerhead water flow itself i.e. pluggage? If so how would I clear this out? My poppet valve is intact and has nothing corroded on it. Recently rebuilt it and my water pump too.

Am I just chasing a bad sensor signal?

Any help would be appreciated.

Thanks,
JimDD
 
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