1987 200hp Mercury outboard overheat alarm constant on

[mainedrive]

I have a 1987 200hp Mercury outboard and the overheat alarm (solid constant alarm) is constant all the time, even on start up. Temp gauge reads 150F when idling for 1/2 hr or so. The warning buzzer started all of the sudden and when I took a look at the motor the overheat sensor wire was completely corroded and broken. I assumed that was the cause and replaced the overheat sensor. That did not satisfy the problem. The overheat sensor wire runs to a terminal block with 2 other tan wires, one goes to the Lubealert module and the other I think goes to the temperature sender in a roundabout way. If I disconnect the tan wire that goes to the Lubealert, the alarm (and all alarms stop). What do I need to look at next?

Joe

[Jim Speros]

Temp sender wire for gauge is tan. Alarm sender leads in harness are tan/ blue. The tan and tan /blue should not connect. The alarm is pretty basic. The key hot, purple lead, powers alarm. Any ground from the overheat sensor or bare wire sounds alarm. The alarm it self can be bad. If you don't have a side mount with key on it control its easy to access. If the tan/blue reads ground at alarm with engine off there is a short. If no ground is detected and alarm is likely bad.

[tlwjkw]

if ya pull tha tan/blu at tha terminal block going to tha oiler module and alarm stops that pretty much tells ya tha motor is not hot.. probably tha module is bad since it starts and is a solid beep instead of an oscillating beep (main function of tha module) as soon as ya turn tha key on............. jmo.

[mainedrive]

Thanks for the quick replies!! Forgive my ignorance on this topic as I am a relative newcomer. This was my late father-in-law's boat that I pulled out of a 5 yr storage and ran it last summer and this summer. Never got to learn from him all the ins and outs of the boat. He did a ton of work on it and kept it in great shape, hence starting up after a 5 yr storage.

I guess it could be a bad module. Overheat sensor (tan/blue) runs to a terminal block that has 2 other tan wires connected to it, one to the Lubealert module and if I disconnect that one, the alarm stops. I will check for a ground somewhere else as the controls are center mounted, and separate ignition switch, (see profile pic), so should be easier to locate faults.


Thanks again.

[Jim Speros]

With warning module disconnected you can easily check remaining alarm system. With Key on use a jumper lead and ground the tan terminal. Alarm should sound. If it does no further checks are required. Replace warning module. Every time you turn the key on the alarm should beep to let you know its working.

Number one maintenance item on your engine is to replace water pump impeller and gearlube annually.

[mainedrive]

Thanks Jim. I have been doing those 2 maintenance items, annually, as well as fogging the engine, only running treated gas.