oil temp probe

[Planegary]

am starting to have an intermittent problem with my oil temp. On occasion it will show a dead gauge then suddenly register normal and occasionally it will bounce from 0 to normal. I am thinking it is the sending unit. My engine is the io -360A1A with the the original sending unit with the canon plug on it. Any suggestions on testing the sending unit before I call the mechanic in? And any idea of the number for the sender? when I looked at aircraft spruce I couldn't find anything so I have come again to the wellspring of knowledge of all things Mooney before I start taking cowlings off and pestering the mechanic

[MikeOH]

I'd check for loose wires before blaming the sensor.  I'd 'wiggle' the connection at the sender first, then connectors, and finally the gauge (which is likely difficult to access).

[N201MKTurbo]

Check your part numbers, but I think this is it:

https://www.aircraftspruce.com/catalog/inpages/oiltempgauges5.php
 

it is most likely a connection rather than the probe. Spruce sellls the connector too.

https://www.aircraftspruce.com/catalog/inpages/canonplugms3106a.php

 

[Planegary]

i have removed the canon plug at both the sensor and the gauge cluster ,sprayed both with contact cleaner and still does it

[Planegary]

I hope I find something other than a $800 sensor. I will keep checking

[Guest]

4 hours ago, Planegary said:

I hope I find something other than a $800 sensor. I will keep checking

Did you open the backshell on the Cannon plug and check inside?  Many times the plugs is simply worn out after 50 years.

Clarence

[Utah20Gflyer]

7 hours ago, Planegary said:

I hope I find something other than a $800 sensor. I will keep checking

I believe you can find them on e Bay for under 100 dollars.  

[Igor_U]

3 hours ago, Utah20Gflyer said:

I believe you can find them on e Bay for under 100 dollars.  

True. I sold mine for less few years ago...  I didn't know I was sitting on gold.

 

[Planegary]

7 hours ago, M20Doc said:

Did you open the backshell on the Cannon plug and check inside?  Many times the plugs is simply worn out after 50 years.

Clarence

didn't do that but i will do that this week and see if i find anything. Thanks for the info.is there any way to test the sensor itself?

[MikeOH]

Yes. By using an ohmmeter.  Unfortunately, I don't know the proper resistance at room temp or at, say, 200 F.

Maybe someone can chime in?

But, if you are seeing a zero reading it sounds more like the sensor going open circuit (hence my previous suggestion to 'wiggle' things!). The fact that it sometimes reads 'normal' suggests the temperature sensitive internal element is functioning properly.  While I am NOT sure about your Mooney oil temp sensor, many of these type of sensors are what is called NTC type: negative temperature coefficient.  That is, they are high resistance at cold, and become less resistive as their temperature increases (which causes the current through them to increase, which is why the meter swings upscale; it is measuring current).

In other words, if the wire/connection goes open, the meter will read zero (current).

[AIREMATT]

Try tapping under the gauge cluster when it is doing it if you have the 6 gauge cluster at the bottom of the panel (like my C does) and see if that corrects it. Might be a connection on the gauge cluster too.
Don’t ask me how I know.

 

[Planegary]

2 hours ago, AIREMATT said:

Try tapping under the gauge cluster when it is doing it if you have the 6 gauge cluster at the bottom of the panel (like my C does) and see if that corrects it. Might be a connection on the gauge cluster too.
Don’t ask me how I know.

 

that was one of the first things I  did and  Iwent so far as to spray the canon plug that connects to the back with contact cleaner and install a new ground from the instrument panel to the cluster

[N231BN]

Yes. By using an ohmmeter.  Unfortunately, I don't know the proper resistance at room temp or at, say, 200 F.
Maybe someone can chime in?
But, if you are seeing a zero reading it sounds more like the sensor going open circuit (hence my previous suggestion to 'wiggle' things!). The fact that it sometimes reads 'normal' suggests the temperature sensitive internal element is functioning properly.  While I am NOT sure about your Mooney oil temp sensor, many of these type of sensors are what is called NTC type: negative temperature coefficient.  That is, they are high resistance at cold, and become less resistive as their temperature increases (which causes the current through them to increase, which is why the meter swings upscale; it is measuring current).
In other words, if the wire/connection goes open, the meter will read zero (current).

If it's a MS-style probe with a cannon plug they actually work opposite of that, an open circuit pegs high and a short goes low. The gauge sends a fixed load to the probe and the higher the resistance, the higher the voltage.

[MikeOH]

6 minutes ago, N231BN said:

On 11/30/2021 at 6:44 PM, MikeOH said:

Yes. By using an ohmmeter.  Unfortunately, I don't know the proper resistance at room temp or at, say, 200 F.
Maybe someone can chime in?
But, if you are seeing a zero reading it sounds more like the sensor going open circuit (hence my previous suggestion to 'wiggle' things!). The fact that it sometimes reads 'normal' suggests the temperature sensitive internal element is functioning properly.  While I am NOT sure about your Mooney oil temp sensor, many of these type of sensors are what is called NTC type: negative temperature coefficient.  That is, they are high resistance at cold, and become less resistive as their temperature increases (which causes the current through them to increase, which is why the meter swings upscale; it is measuring current).
In other words, if the wire/connection goes open, the meter will read zero (current).

If it's a MS-style probe with a cannon plug they actually work opposite of that, an open circuit pegs high and a short goes low. The gauge sends a fixed load to the probe and the higher the resistance, the higher the voltage.

Ah, thanks!  Certainly can test by pulling the wire off the sender; maybe the op is dealing with a intermittent short, somewhere along the wire run.