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1996 Mercury 2 stroke/ 4 cyl C40ELPTO - Suspect False Overheat Warnings

M

mbp

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1996 Mercury 2 stroke/ 4 cyl C40ELPTO - Suspect False Overheat WarningsGetting various warning beeps. Usually the long beep that is an overheat. (See other posts…continuing saga).Replaced the impeller - no signs of overheat, despite several past overheat warnings. Strong flow out the pisser….always has been. Motor does not have a thermostat. Was not built with a thermostat. Ran the motor for an hour after the impeller install and shot the top plug with IR thermometer - 108F. Ran the motor several hours, got a chirp-beep - top plug 113F. Subsequently, my wife ran it for over an hour and got a long beep. She felt the engine cover - it was not warm.When we first turn the key on we either get no beep, a short beep, or one long lasting beep.I am guessing the warning system is bad. Cannot find anything about the warning system in the OEM repair manual. Anyone have a fix for this?
 
Since you get two different beep signals you have an OT module, if I recall get on the Starboard side of the engine and look for a 1" or so, black module just below where the top cowling rests on the midsection cowling. The identifying item is the presence of a tan wire in the wiring to the input connector. It could be your problem. Trouble shooting is just remove the connector.

Get aft of the engine and look at the cooling water jacket cover through which the spark plugs are mounted. On the left, lower side of that plate, look for a tan wire imbedded in the plate to the switch which is held in place with one small screw. Follow that tan wire back to the input wiring harness on the Starboard side and it should be a bayonet plug into a Y connection. Open the cicuit there.

One of those actions should locate your smoking gun.
 
Last edited:
Texasmark said:
Since you get two different beep signals you have an OT module, if I recall get on the Starboard side of the engine and look for a 1" or so, black module just below where the top cowling rests on the midsection cowling. The identifying item is the presence of a tan wire in the wiring to the input connector. It could be your problem. Trouble shooting is just remove the connector.

Get aft of the engine and look at the cooling water jacket cover through which the spark plugs are mounted. On the left, lower side of that plate, look for a tan wire imbedded in the plate to the switch which is held in place with one small screw. Follow that tan wire back to the input wiring harness on the Starboard side and it should be a bayonet plug into a Y connection. Open the cicuit there.

One of those actions should locate your smoking gun.
Click to expand...


Ok. Thank you. Got the long beep yesterday. Turned motor off and ignition back on. Long beep continued. Opened the bullet connectors on the two blue oil reservoir and tan/blue connector and long beep continued. Logic tells me a bad warning module. New one comes tomorrow.
 
Long or continuous alarm is the OT sensor. Oil is modulated for engines with the modulation module allowing the operator to distinguish between the two. On engines without the module you get a solid alarm for both and you have to figure out which is causing it.
 
Texasmark said:
Long or continuous alarm is the OT sensor. Oil is modulated for engines with the modulation module allowing the operator to distinguish between the two. On engines without the module you get a solid alarm for both and you have to figure out which is causing it.
Click to expand...

ok. Thank you.
 
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