50HP Mariner alarm Please help

My 1983 50HP 3cy 2 stroke has that incredibly irritating alarm. From what I have been told the alarm goes off in 3 cases.

1. not enough oil. (oil system is currently bypassed and mixed manually 50:1)

2. Overheating due to no water being pumped. Brand new impeller and peeing like normal.

3. Thermostat bad. This is what I think it probably is.

The motor is a little difficult to start, and the alarm doesn't start until you throttle up to about 25%. It is also a constant alarm, not a beep beep beep.

I have tried to find thermostat housing with no luck. The diagrams I have seen makes it look like it is right above the 1st cylinder spark plug. Maybe I’m dumb, but just not finding it. Lastly the serial number is B13......

Thanks for any help you guys can give.

Post a pic of your motor.I believe your right, it is above the top cylinder.2 or 3 bolts to remove.

Here are some pics.. I'll try to explain what we are looking at and what I have done. I'm not very mechanically inclined so I appolgize for the vague/inaccurate descriptions.

Motor Cover, 83 Mariner 50HP 3Cyl


Right side of motor, notice the top lefthand side, closer photo next


Notice right in the middle of this photo the tan wire. It is connected to a a block which I was told had something to do with temp control. The other side of the wire runs to the top cyl.


Here is a closer look at the top cyl and the wire that runs into it.



Lastly a photo of the rear. The plate you see closest is the cover mounting bracket. After removing that there are 6 bolts that hold on a cover. After removing the plugs and that cover, there appears to be nothing but the holes that the spark plugs go into. There was some oil and residue in this area as well.

Constant beep normally means overheating. If its not getting too hot, its prolly the thermo.

Is there an oil warning module on this unit,I know you disconnected the oil,but is the module still connected?

If there is do you have three wires going to it a black, tan and a purple, if so next time it goes off try unplugging the purple wire.

The thermostat is on the side of your motor, the side you don t have pictures of, at the top of the power head.

See if this picture helps locating it.

rick50 said:

See if this picture helps locating it.

Click to expand...

I'm not seeing what the picture is showing. Here is a photo of the opposite side of the motor:



And here is the only purple wire I see, and it is labeled as VIO

Did this motor have an oil tank on it?

If you know the serial number you can go to marinepartsplus.com and look at a break down of the engine. Maybe that will help you.

rick50 said:

Did this motor have an oil tank on it?

If you know the serial number you can go to marinepartsplus.com and look at a break down of the engine. Maybe that will help you.

Click to expand...

I'm not sure on the oil tank, I purchased this boat knowing the alarm problem thinking it would be a simple fix.
I here is the link to my motor, https://www.marinepartsplus.com/catalog/mariner/serial/50_3_CYL/+16404. I have looked thru every category and see nothing on a thermostat. I am begining to wonder if this was one of those unusual Mercury built motors that didn't have a thermostat?