1992 75hp Mercury 2-stroke, overheating warning

[redrock09]

I am having problems with a overheating warning tone. Cant find the problem why it is alarming. Started up the motor and it has a continuous tone, so it cant be overheating right?! The tell-tail is peeing like normal. Checked/replaced thermostat and poppet, both looked in good condition. Disconnected the oil tank to see if that was the problem, nope, tone still on.

Send help.

 

[Texasmark]

On later models of that enigne, like late '90's on, there is an 8 pin connector in the engine where the remote control electrical cable attaches. Pin 3 of that harness has a tan or tan/light blue striped wire which is the "ground" wire for activation of the horn.

Pigtailing on the engine side are 2 sensors: Oil tank level alarm and over temp. If either shorts the wire is grounded and you get the alarm.

On the back of the block on these later engines and surely yours, is a tan wire which is attached to the OT sensor buried in the water jacket plate covering the rear of the block...held in place with one screw. Follow this tan wire to the nearest bayonet connector and disconnect.

Try your horn again. If it is off, the sensor is shorted. If it is still on you have a wire shorted somewhere between the low side of the horn and ground....battery -.

 

[redrock09]

Texasmark-

Thanks for looking it up. I checked and disconnected both the OT and the oil tank level wires. Both connections looks new and no corrosion. Still getting an alarm. Will disconnecting either of the wires trip an alarm?

 

[emoney]

Have you put a infrared thermometer on the heads to see if they are, in fact, overheating? You can pick those up at Harbor Freight for under $30.00 and it's a great tool to own for a bunch of different reasons.

 

[N1265]

Just wondering at what temp the heads need to be to set off a properly working temp alarm ?

 

[Texasmark]

The OEM stat in my 2002 90 was stamped 143F opening temp. The 2002 115 I acquired last year had a 125F stat and I know not of the origin. The service manual for all these series of engines, including your year-model states that the alarm temp sounds at 195 (with tolerances of probably 5-10%) and ceases when the temp has dropped to 175 or thereabouts....forget that number.
I have a farm and my HF Infrared non contact gets used quite often.

 

[Faztbullet]

Disconnect oil warning module...