Oil Temperature Maxed out

[crxcte]

Coming back from Memphis today I looked down at the gauges and noticed the oil temp was maxed out.  Oil pressure and cylinder temp look OK.  To be safe I took it down to the next paved airport where nobody lives.  The oil was a little low I added a quart.  Did seem any hotter than usual.  I started the plane after 20 minutes and it looked as though the oil temp may of dropped a little but was still high.  I took off to the next airport and stopped again.  Bought some oil and filled to 8 quarts.  After about 45 minutes I started the plane and it was maxed in oil temp.  I'm pretty sure its not the engine but the monitor. 

See attached image.  Anyone have the same issue with this gauge?

 

[Parker_Woodruff]

I'll tell you for a fact those gauges are not very linear in their range of operation...but at the same time I wouldnt take any chances.

[Piloto]

Did the temperature ever came down with engine off? If the temp never came down you have a shorted probe wire, probably due to shafing. Check wiring. You can also check the probe calibration with a temp controlled soldering iron, both inmersed in a small cup of oil. If the oil pressure never came down, it is very likely a temp probe problem

José

 

[crxcte]

When the master was turned off the oil temp came all the way down.  Then I turned the master back on and oil temp gauge went over to the max high temp. 

I will have to find a manual to check the oil temp probe tip location.  I'm assuming it is at the oil pan area.  Is it simular to the EGT tip?

Chris

[scottfromiowa]

I had the same thing happen in my M20E several months ago during a trip to Hot Springs, Arkansas.  I had an oil temp gauge in six pack "pegged".  I did a pre-cautionary landing although the cylinder temps and oil pressure were fine.  Gauge would zero when off and then jump back up with master on.

Was NOT the probe, although I ordered a new probe just in case.  Was the failure of one of the wires from the probe going back to the gauge.  A simple repair of the wire and all was well.

Hope this is your problem too.  Good luck,

 

Scott

[scottfromiowa]

The probe is NOT down in the oil pan.  It is right below mags if I remember correctly.  Trace back the wires out of the firewall.  I believe it is two wires (relatively light gauge) wrapped in plastic sheath.  Scott

You only need to remove the top cowl to expose the wires/probe location.  Probe/wires are on firewall side of engine.

Scott

[KJATCt]

On my E the probe is just in front of the spin on oil filter on the adaptor plate.

[GeorgePerry]

I'd have a qualified shop do a calibration test to the temp guage.  That's the best way to determine if you've got an indicator issue of a real problem with temps

[scottfromiowa]

With respect...my failure to past peak temp was IDENTICAL to what you discuss...I would start with checking the wire BEFORE I went to probe/gauge/indicator failure.  My fix was easy and INEXPENSIVE.  Based on your oil pressure being in the green and cylinder temps being fine...and NOT being low on oil...

[crxcte]

I will check the wires.  Thanks all. 

[N201MKTurbo]

These gauges will show a max indication when the probe is open not shorted. With my old M20F it was usually the connector on the probe. You can check the wireing by disconnecting the connector and shorting the two pins together. The meter should indicate zero, if it does not then there is a problem elsware in the wireing. If it does then disassemble the connector and squeeze the female pins to increase the spring pressure, or spend $50 for a new connector and an hour of labor to change it.

[Immelman]

Could be the oil system, the engine, the sender, or the gauge. Perhaps an experiment (sender removed and placed in boiling water?) would help?

My sender/gauge consistently indicate 15-20dF higher than actual -- at least at ambient temperature. I recently bought an oil temperature probe for my JPI monitor and will add that in soon, to supplement the ship's gauge.

[crxcte]

I checked the wiring yesterday and all were connected.  Thought may be one of the 2 wires going to the probe might of been too tight so reset some ties.  Flipped on the master and the gauge read zero so I cranked it up and it immediately went to 200 F and 5 minutes later running about 17" of manifold pressure, the temperature maxed out.  I'm think its a gauge issue now.

[scottfromiowa]

My wires were connected, but one of the wires was broken inside the sheath...

[crxcte]

The wire used on my oil temperature gauge to outside the firewall is stainless steel shielded around an aluminum braided wire. 

Then that wire is housed in a cable with many other stainless steel shielded braided wire.  This type of wire just doesn't break easily.  They don't even cut easily, but there is always the first time.  

 

[scottfromiowa]

O.K. Chris.  Totally different than my wires that are light gauge and lightly shielded.  Good luck sorting it out.  Post a note to your solution.

[carusoam]

CRXCTE,

Things to consider......

After all of the super sleuth work that you have completed, I am going with the sensor not working right at the hot end....

The temperature gauge is simply a voltage meter (calibrated in degrees F) reading the voltage difference across the variable resistance of the sensor, using the electricity provided by the ship's battery.

[1] Broken wire would give a constant reading.  Maximum resistance = maximum reading.

[2] Shorted wire (crossed) would give the opposite, but constant reading.   minimum resistance = minimum reading.

[2a] No power to the gauge is certainly going to read minimum.  (no voltage difference)

[3] Sensor is of the variable resistor type, (thermistor).   Resistance increases with temperature.

[4] The sensor seems to be working, but improperly.  Shows cold when cold, but shows well over heated when hot.

[5] If the oil was really that hot, you would surely notice a significant drop in oil pressure.  A thermocouple type thermometer from a cooking store would help you understand what the real temperature is.

[6] The gauge itself could be at fault.  The gauge is in the nice environment of the cockpit.  The thermistor is in the harsh, hot and vibrating environment of the engine.  Lastly, you may also consider that the full battery voltage may not be getting to the system (least likely, but something to consider).   See item [7] battery voltage is delivered internally through the cluster gauge connector.

[7] Super lastly...The indicator is reading a collective resistance of all the wire, connectors and thermistor.  If the connectors have increased in resistance for some reason, the indicator will change as things warm up and then go off scale.  There are two connectors to check, one at the sensor in the engine and one at the back of the instrument cluster.  (this would be your lowest cost fix)  Disconnect the connector, use contact cleaner, reassemble the connectors.

[8] The battery voltage isn't running incredibly low is it?  This would cause a whole new set of issues anyway...

That's why I vote thermistor being most suspect, gauge being the next and wire/connectors being the third most suspect.

Best regards,

- anthony -

PS.  I looked up the part number for a 1965 and 66 mooney M20C and E.  It is listed as bulb, oil temp AN5525-1

Aircraft spruce lists a similar one (possible identical) for $145

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

If nothing else, check this website.  It will give you a good idea of what you are looking for....

Jose: does this look right to you?

PPS:  The EGT is a thermocouple and does not look or work anything like the oil temperature sensor, other than generically it has two wires going into a metal sensor.....

Best regards,

-a-

[Mcstealth]

Quote: carusoam

CRXCTE,

Things to consider......

After all of the super sleuth work that you have completed, I am going with the sensor not working right at the hot end....

The temperature gauge is simply a voltage meter (calibrated in degrees F) reading the voltage difference across the variable resistance of the sensor, using the electricity provided by the ship's battery.

[1] Broken wire would give a constant reading.  Maximum resistance = maximum reading.

[2] Shorted wire (crossed) would give the opposite, but constant reading.   minimum resistance = minimum reading.

[2a] No power to the gauge is certainly going to read minimum.  (no voltage difference)

[3] Sensor is of the variable resistor type, (thermistor).   Resistance increases with temperature.

[4] The sensor seems to be working, but improperly.  Shows cold when cold, but shows well over heated when hot.

[5] If the oil was really that hot, you would surely notice a significant drop in oil pressure.  A thermocouple type thermometer from a cooking store would help you understand what the real temperature is.

[6] The gauge itself could be at fault.  The gauge is in the nice environment of the cockpit.  The thermistor is in the harsh, hot and vibrating environment of the engine.  Lastly, you may also consider that the full battery voltage may not be getting to the system (least likely, but something to consider).   See item [7] battery voltage is delivered internally through the cluster gauge connector.

[7] Super lastly...The indicator is reading a collective resistance of all the wire, connectors and thermistor.  If the connectors have increased in resistance for some reason, the indicator will change as things warm up and then go off scale.  There are two connectors to check, one at the sensor in the engine and one at the back of the instrument cluster.  (this would be your lowest cost fix)  Disconnect the connector, use contact cleaner, reassemble the connectors.

[8] The battery voltage isn't running incredibly low is it?  This would cause a whole new set of issues anyway...

That's why I vote thermistor being most suspect, gauge being the next and wire/connectors being the third most suspect.

Best regards,

- anthony -

PS.  I looked up the part number for a 1965 and 66 mooney M20C and E.  It is listed as bulb, oil temp AN5525-1

Aircraft spruce lists a similar one (possible identical) for $145

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

If nothing else, check this website.  It will give you a good idea of what you are looking for....

Jose: does this look right to you?

PPS:  The EGT is a thermocouple and does not look or work anything like the oil temperature sensor, other than generically it has two wires going into a metal sensor.....

Best regards,

-a-

[crxcte]

Thanks for the information.  The battery power has not been a problem. 

I unplugged the wires at the engine then turned on the master with the engine cold and the temp went to max.

I shorted the wires at the engine then turned on the master with the engine cold and the temp was zero.

Went I plugged the wires back into the engine then turned on the master with the engine cold the temp went to ~180 degrees.

So I'm thinking thermistor bulb.

 

[carusoam]

Have you tried the plug at the instrument end yet?   In the event that you have picked up additional resistance (contact corrosion) at this connection, it would be additive to the reading.....

Unlikely, but not hard to try......

-a-

[crxcte]

As an update, the problem was the gauge.  

[scottfromiowa]

Thanks for the update.  Glad you figured it out and got repaired Chris.

[Jsavage3]

I had similar indications a while back. 

Took the top cowl off and the oil cooler felt cold to the touch while the oil temp guage was at red line...that should not be the case.  The vernatherm was bad.  Replaced it and everything has been just right ever since.

 

[Hank]

This happened to me once after an oil change. Turned out the safety wire on the filter was grounded out. New wire, more careful approach with the pliers, and everything has been fine.

[kortopates]

Quote: Hank

.....Turned out the safety wire on the filter was grounded out. New wire, more careful approach with the pliers, and everything has been fine.