Can lower OPEN value of overheating sensor, sound false alarm?

[Chovus]

I have problem with my outboard. I dont know is it cooling system or sensor.

I dont know is the alarm that I get, false or positive. After 2minutes working on 95% of full throttle, I get buzzer alarm and the engine go to 50% throttle.

I measure overheat sensor, when sensor close and open.
1. it CLOSE at 125'C (257F)
2. and it OPEN 85'C (185F)
The OPEN value should be 110'C.

How sensor works with other electronics? Is he giving a signal that machine didnt cool down for certain period of time and the he activate "problem"?

The sensor for Tohatsu M70C 2002 is around 140eur, and it is expensive just to try it. I can not return it. So guys, can the sensor, sound alarm for a FAKE PROBLEM, with that values that I meassure?

Thanks in advance

Sorry if my English is bad

 

[Chris1956]

Thermostats usually open ay 143*F. Engines will run at 180* F or less.

So unless you measured your overheat sensor wrong, it is really out of whack. Closing of the sensor triggers the alarm. So yours doesn't close until 45*F above the boiling or water?

 

[Chovus]

Thermostats usually open ay 143*F. Engines will run at 180* F or less.

So unless you measured your overheat sensor wrong, it is really out of whack. Closing of the sensor triggers the alarm. So yours doesn't close until 45*F above the boiling or water?

Thanks for your support @Chris1956 .
I tested also thermostat and it start to open at 61-62'C (~143F). At 88'C it is open 6mm (0.23") , I didnt tested higher temp to see where it goes. I only have boiling water. Still, I dont know what is maximum open (or diagram), cant find on internet.
Tohatsu Part Number: 3C7-01030-0 / 353-01032-0

Overheat sensor is bimetal I think this model:
New Genuine OEM TOHATSU OVER-HEAT SENSOR ASS'Y 3F3761720 3F3-76172-0 60 70 HP

I know it is strange, but that is chart (in picture), for my Tohatsu 2-stroke. So, you say, that my outbard is overheating (closing the sensor = trigger alarm).
p.s. I pay a guy to change impeller. But I am not sure he chage it :-(
p.p.s. Can that high differrence in temperutre to open again be a problem (85'C (185F) vs factory default 110'C (230F))?

 

[Chris1956]

That table is very strange, but just for your motor. The rest of the entries looked about what you would expect.

Even if the coolant water was pressurized to 7lbs, like an automobile, the coolant water would still boil, before the sensor closed.

I am hoping the table is wrong.

You said you tested the sensor. How did you get the water to become 257*F? You would have needed to test it in oil, with a candy thermometer. Hopefully wifey didn't find out..

 

[Chovus]

That table is very strange, but just for your motor. The rest of the entries looked about what you would expect.

Even if the coolant water was pressurized to 7lbs, like an automobile, the coolant water would still boil, before the sensor closed.

I am hoping the table is wrong.

You said you tested the sensor. How did you get the water to become 257*F? You would have needed to test it in oil, with a candy thermometer. Hopefully wifey didn't find out..

I tested in closed room with hot air on low with SMD rework station and using Digital thermometar to take a measure. I set SMD station compressor to low airflow, temp on 150'C (300F) (can set from 150-400'c) to heat it slowly from a short distance, and I think that meassrment I get are good. I try 5x. It close at 125'c and open again at 85'c (when I slowly turn airfow to lowest)
The Table is from owners manual, and I checked on other languages, it is same. Also checked in the Service manual for all 2-strokes 3 cylinder (60-70hp) and the temps are unreal.

 

[Chovus]

Hopefully wifey didn't find out..

 

[Chris1956]

Not sure what to say. Those temps don't make any sense to me.....