oil temp gauge

[DrQuinn]

Since purchase my oil temp gauge doesn't work.  We pulled out the sensor, shorted it and it registered.  We dipped it in boiling water and it read approx 232.  

I do have an engine analyzer that has a working oil temp gauge but I'd like to have the quick visual (besides the analyzer is only really supposed to be a secondary).

Does anyone have any thoughts?  I've attached a picture of where the probe is.

 

Dave

[N201MKTurbo]

If it doesn't work how did you get the 232 reading?

[N201MKTurbo]

http://www.aircraftspruce.com/catalog/inpages/rochoiltemp.php

[DrQuinn]

1 hour ago, N201MKTurbo said:

If it doesn't work how did you get the 232 reading?

It worked in boiling water, it worked when shorted out, it doesn't work plugged into the engine.  Consider it works in theory, just not in practice.

[DrQuinn]

1 hour ago, N201MKTurbo said:

http://www.aircraftspruce.com/catalog/inpages/rochoiltemp.php

i suppose I could do that, just doesn't make sense that it works fine when not needed; that's why mechanic was questioning its placement.

[N201MKTurbo]

2 hours ago, DrQuinn said:

i suppose I could do that, just doesn't make sense that it works fine when not needed; that's why mechanic was questioning its placement.

I've never seen one plugged in there.

[Guest]

7 hours ago, DrQuinn said:

It worked in boiling water, it worked when shorted out, it doesn't work plugged into the engine.  Consider it works in theory, just not in practice.

Is it the correct probe?

Clarence

[DrQuinn]

3 hours ago, M20Doc said:

Is it the correct probe?

Clarence

I only assumed it was, but I suppose I really don't know.  I will check for any markings if I get a chance later today.

[Yetti]

Check ground strap to engine and clean.   Does it read when screwed in and you run a jumper to the airframe to the base of probe.

[Yetti]

+1 for not having the firesleeve held on with a nylon ty wrap

[cnoe]

13 hours ago, DrQuinn said:

... just doesn't make sense that it works fine when not needed; that's why mechanic was questioning its placement.

When you pull out the probe is there oil in the hole? And are you sure that $0.01 import vinyl but connector is making good contact?

It's gotta be one of 3 things:

Bad probe: you seem to have dis-proven this but it COULD be intermittent.

Bad wiring: use an ohm-meter to check continuity between the probe contact and the gauge contact (simple). As noted earlier, a good engine ground is also required.

Bad gauge: you seem to have dis-proven that too, but that too could be an intermittent problem.

Mine quit registering a couple of months ago and it turned out to be a poor crimp on the ring terminal. That repair cost me about $0.25 (using a quality nylon-insulated ring terminal).

 

[DrQuinn]

7 minutes ago, cnoe said:

When you pull out the probe is there oil in the hole? And are you sure that $0.01 import vinyl but connector is making good contact?

It's gotta be one of 3 things:

Bad probe: you seem to have dis-proven this but it COULD be intermittent.

Bad wiring: use an ohm-meter to check continuity between the probe contact and the gauge contact (simple). As noted earlier, a good engine ground is also required.

Bad gauge: you seem to have dis-proven that too, but that too could be an intermittent problem.

Mine quit registering a couple of months ago and it turned out to be a poor crimp on the ring terminal. That repair cost me about $0.25 (using a quality nylon-insulated ring terminal).

 

Thanks for the great advice and giving us something to chase.  $0.25 ... that's probably $0.32 Canadian.

[N6758N]

5 hours ago, DrQuinn said:

I only assumed it was, but I suppose I really don't know.  I will check for any markings if I get a chance later today.

I think I have an old oil temp probe I removed from my EDM 900 install, pay the shipping and its yours. 

[DrQuinn]

38 minutes ago, N6758N said:

I think I have an old oil temp probe I removed from my EDM 900 install, pay the shipping and its yours. 

Awesome, thanks.  I'll let you know if I need to take you up on that offer in the next day or two.

[carusoam]

Dr. Q, don't go away so fast....

Summary of the observations...

1) that probe is a thermistor.  It's resistance changes with temperature.  Incredibly stable, and resistant to age, compared to everything else...

2) it's reading is dependent on voltage supplied and grounding quality of its connection to the instrument panel.

3) The OEM location is usually in the engine block to also give a warning of a low oil level.

4) It is possible that the thermistor has been relocated when the engine monitor got installed.

5) Check where the engine monitor is getting its OilT data from.  Expect a thermocouple has been placed in the original OilT thermistor location.

6) When testing to see if the thermistor is working.... measure it resistance, according to the Rochester data provided by Rich above...

Electrical sender (Probe) 3080-37 for cluster-type instrument.  

5/8"-18, 10/32 Thread
Resistance (Ohms)
Note: Used 177-18 Thermistor curve “E”

• 100°F =497Ω 
• 150°F =179Ω 
• 200°F =72Ω 
• 250°F =34Ω

7)  note: Small amounts of resistance added to the wire and mounting is going to affect the reading.

8) how this system works... ship's power/voltage is supplied at one end to supply current. There will be a voltage drop across this resistor.  The oil Temp indicator is somehow measuring current through the circuit, via a voltage drop across a known resistor (upstream?)

 

Anyone know what is actually getting measured for the OilT circuit? Something is amiss and it is probably there...

 

PP thoughts only, not an instrument guy...

Best regards,

-a-

Edited May 18, 2017 by carusoam

[DrQuinn]

2 minutes ago, carusoam said:

Thanks for confirming the placement doesn't seem right Carusam.  I was told that the oil temp probe for the engine monitor is in the oil pan, not a likely spot for the OEM probe I wouldn't suspect.  Maybe another analyzer probe is using the spot; I will try and map all the probes on the engine.  As you describe it, it makes sense that the gauge just measures the current that gets through the circuit after it passes through the temperature sensitive resistance of the probe.

Thanks again.

 

[carusoam]

Often POHs show where the important sensors are placed and why they got to where they are...

The C's POH doesn't seem to have it.  A look into the O360’s manual from Lycoming may be the place to go...

Typically, the pilot would be interested in the oil T & P as it leaves the oil pump.  These are the quality measurements for the oil that is being delivered to the engines parts...

Any red lines or yellow zones and of course the green zone, on the gauge, are related to the temp and the location of it's sensor.

In order to make go/nogo decisions based on what the gauge is reading, it is helpful to have the right sensor, sitting in the right location...

Since a filter may have been added to the plane, an STC document might be covering the sensor relocation too.  If the ranges on the indicator are changed to match the STC the indicator on the panel may have been updated (repainted) to match.

Back to the original challenge.  If the voltage is being delivered to the sensor, and the thermistor's resistance is in the range of the Rochester chart given, the challenge is probably back at the indicator in the panel... lots of connections to be cleaned..?

PP things to think about...

Best regards,

-a-

[Andy95W]

Your probe location is the same as both M20Cs that I've owned.

Your probe itself is different from mine.

[Guest]

I think your plane falls into this age range? If so then a Rochester 3080-13 probe

Clarence

 

[Rjfanjet]

Any chance you have this chart for a 68C? Just did a lot of work on the engine and my temp gauge pegs to full hot. We looked at the original probe and it looks like it was fixed with silicone. Just want to do things right.

Thanks

[Rjfanjet]

Found the answer. MS part replacement.