135 hp Mercury 2.0 V6 - Tempurature warning alarm sounds

aayjay

Seaman Apprentice
Joined
Apr 22, 2011
Messages
37
My alarm gives a constant tone after around 15-20 minutes at idle in gear, water temp gague is working, and seems to be alright, water temp reads around 120 at idle and goes up to 145 at speed, but the alarm goes off at idle. I shut off the engine lift the motor and no fouling in the water intake.. drop the motor and restart and no tone. the impeller is pumping water in a constant flow (has been replaced recently). Sounds like an electrical issue in the alarm system, but I dont know where to begin. Advice?
 

j_martin

Admiral
Joined
Sep 22, 2006
Messages
7,474
Re: 135 hp Mercury 2.0 V6 - Tempurature warning alarm sounds

On the starboard side of the engine, over the switchboxes, there's a terminal strip with 2 terminals on it. One is purple wires...that's the 12V feed to the oil alert. The other has one wire from the OT switch, one from the oil alert, and one going up to the alarm buzzer.

If you ground that screw, the alarm will sound. That's how you know you're looking at the right wire. Don't ground the purple one, it'll just blow a fuse.

If, while the alarm is sounding, (long idle) you disconnect the OT sender and oil-alert wires from that screw, it should stop. If it doesn't, there's a short in the harness.

If it does, touch the OT wire to the screw. If it alarms, either it's hot or the switch is bad. If you touch the head and don't stick to it, the switch is bad.

Then do the same with the oil alert wire. Yes, the oil alert could be faulting out in that way. If it gives a solid tone, the oil alert module is bad.

hope it helps
John
 
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