High Oil Temp - Vernatherm or Sensor or Other?

[JamesClarkIV]

I have had 3 unusual oil temperature events over the last 6 flights. RV7A IO-360-M1B with ~1000hrs of normal 180F-200F oil temp readings. I will post engine data pictures below in hopes folks can help me identify possible causes.

First occasion was on a few laps around the pattern to warm the oil prior to an oil change. Engine oil temp was normal until 2nd landing approach, oil temp rapidly rose from 203 to 230(yellow) after pulling power for landing during final.

I then changed the oil. And did 3 more laps around the pattern after oil change with no issues observed.

Next flight was 3 hour trip VA to GA. No issues observed.

Next flight was 3 hour return GA to VA. The oil temp issue showed twice. Once early in the flight just after top of climb at 9500. Sudden oil rise occurred just after climb level off power adjustments. Rise was 208 to 236(yellow) in 60 seconds. I enriched mixture and pulled throttle some and oil temp cam back down. I decided to stay high and continue home rather than land.

At the end of the same 3 hour flight after descending from 11,500 to 1300 pattern altitude, and after turning final and pulling power, the oil temp rapidly rose from 210 to 245 in the span of 30 seconds.

Could this be caused by faulty sensor? Could this be caused by vernathern that is opening and suddenly shunting hot oil away from oil cooler and dumping it onto the oil temp sensor (is this sensor at the output of the oil cooler return line?).

I will attempt to post engine log pictures below. Thanks in advance for any ideas.

[lr172]

Originally Posted by JamesClarkIV

\
Could this be caused by faulty sensor? Could this be caused by vernathern that is opening and suddenly shunting hot oil away from oil cooler and dumping it onto the oil temp sensor (is this sensor at the output of the oil cooler return line?).

.

Yes. oil temp can't rise 35* in 30 seconds and vernatherms don't really fail like this. Likely a bad crimp at terminal on OT sensor. vibration patterns are changing as you pull the power back and is likely adding resistance at that bad crimp or loose connection.

Even if the VT was opening and closing erratically, I don't think the cooler can shed 35* in most cases. I thought is was closer to 20* or less, but not sure.

I would definitely start with OT sensor wiring.

Sensor is on the return side of the cooler, so when the VT is closed, it reads the temp of the oil returning from the cooler. However, VT's usually either stop working or fail to fully close the port. It would seem implausible to me to have a VT suddenly open and then magically close 10 minutes later. It is just a piston with with piece of wax that changes size with heat. Not very sophisticated. They typically fail by not closing or only partially closing. Having one suddenly open just isn't how they fail.

Larry

[JamesClarkIV]

Event 1:
https://jamessclarkivdotcom.files.wo...nt1.png?w=1280

Event 2:
https://jamessclarkivdotcom.files.wo...nt2.png?w=1280

Event 3:
https://jamessclarkivdotcom.files.wo...nt3.png?w=1280

[lr172]

Originally Posted by JamesClarkIV

Event 1:
https://jamessclarkivdotcom.files.wo...nt1.png?w=1280

Event 2:
https://jamessclarkivdotcom.files.wo...nt2.png?w=1280

Event 3:
https://jamessclarkivdotcom.files.wo...nt3.png?w=1280

Your first chart shows erratic OT readings long before you pulled the power back. Up and down oil temps is likely a sensor issue NOT a VT issue. It is a simple thermistor that changes resistance based upon temp. Any resistance added by the wiring will show as additional temp beyond the sensor reading. Resistance going up and down is more a sign of a minor wiring flaw that will be hard to find.

[Bavafa]

I have had this issue with my Garmin setup. As others mentioned, oil temp doesn't go up and down so quickly and mine has gone all the way to 360F in just a few seconds.
I have recrimped my wire multiple times, including solder joint. It is good till a few flights later. I changed sensor now and we will see if this will fix it.

[JamesClarkIV]

Thank you both for your replies. I have ordered a replacement sensor that hasn't arrived yet. I was able to wiggle the wiring near the sensor and got a few degrees of temperature deviation from room temp, but wasn't able to repeat it with more wiggling. I did try reheating the blue solder splice connectors on both wires and subsequently flew the aircraft 6 laps around the pattern without any issue. Will post back once I replace the sensor and get more flights.

[lr172]

Originally Posted by JamesClarkIV

Thank you both for your replies. I have ordered a replacement sensor that hasn't arrived yet. I was able to wiggle the wiring near the sensor and got a few degrees of temperature deviation from room temp, but wasn't able to repeat it with more wiggling. I did try reheating the blue solder splice connectors on both wires and subsequently flew the aircraft 6 laps around the pattern without any issue. Will post back once I replace the sensor and get more flights.

If you can get a temp change by wiggling the wires, crimping on a new terminal comes before replacing the sender.