88 johnson overheat alarm

Hi guys.  Im out now and was havibg trouble getting the boat started.  Killed batt for motor.  So i switched out trollling motor battery and got it going.  Now i left it idle while i switched batteries again now my overheat alarm sounds constantly while key is on.  Water is pumping through like it should i know its not overheating.  Any suggestions on fixing this?  

V4 Cross flow is a good motor. Got the model #? Or do you know the year? 

Prior to 1996 Warning Alarms

No Oil- Beep every 1/2 second

Low Oil- Beep every 30 seconds

Overheat- Constant beep

1996 to Current all Warning Alarms are constant for a 10 seconds and the corresponding light illuminates on the tach or system check gauge.

Same as the OP's issue...

If you have oil in the reservoir, and you are certain your motor is not overheating, the most likely cause is the overheat sensor or the low oil sensor in the reservoir. 

Disconnect both and see if the alarm stops.  If it does, replace that sensor.  

The sensor is essentially a resistor, if it gets too hot, it allows voltage to the horn (audible alarm)

If the overheat sensor has failed I would replace it.  The low oil sensor in my opinion really isn't a big deal.  The low oil sensor simply ensures that there is oil in the reservoir, it has no idea if oil is actually being delivered to the engine. 

I think it is a good idea to check the oil level before each trip to ensure that the engine is actually using oil.  Remember, the best a two stroke ever runs (most performance too) is just before it blows up.  

One other thought, it could be the oil sensor.  

The alarm means overheat, or no oil.  There is a magnet in the oil reservoir sensor, sometimes it falls off, and ends up in the bottom of the oil reservoir, and then you get the dreaded beeeeeppppp!!!!

If the alarm is constant, and sounds at start-up on a cold engine, I agree, no way it could be overheating.  

I would suspect the sensor is shorted to ground.  

I would locate the sensor and disconnect it and see if the alarm goes away.

If it does, replace the sensor.  

They were great motors but I lost one because the port pump failed.   Alarm went off.  I shut it down and let it cool off.  I checked the oil tank and it was good.  I was 7 miles offshore on Michigan so I fired it back up and went in.  Alarm never sounded again. I fried both cylinders on that side of the motor.  Sold it for parts.  It was old enough to not rebuild.

Was a vro.  Now i mix the gas.

Is it a VRO? If so, get oil the pumps checked.