failing oil temp sensor

[prkaye]

On a x-country flight the other day I believe I began experiencing a failure of my oil temperature sensor. The oil temp indicated on my EFIS began rapidly fluctuating within a range of about 6 to 8 degrees Fahrenheit. I noticed it when the fluctuations started peaking up over 220 degrees nudging into the yellow arc. I powered back, and the mean indicated oil temp gradually decreased into the low 200's, but the rapid fluctuations continued (bouncing around continuously, sometimes jumping by more than 6 degrees almost instantaneously).
All other readings were normal, all CHTs and EGTs showed normal, and there was no change in power or engine noise.
Question - does this sound like a typical mode of failure for the oil temp sensor? Is it unusual for these to fail after only 200 hours??

[Tom Martin]

phil
It sounds like a sensor issue but I would talk to a mechanic to rule out an actual engine issue.
I have had sensor issues in that amount of time but usually the temperature swings are much higher. Check all the connections, spade terminals are suspect, and make sure that none of the wires for the sensor are touching. The covering on some of these wires is not all that special. Also try clamping a ground wire directly to the sensor, as I have also experienced a bad ground.

[prkaye]

So on my 2hr return flight yesterday I watched oil temps more closely. It was a cooler day, so the temps never got above 200 degrees. I noticed they were much more stable at lower power settings where the oil temp was down between 180 and 190. In that temperture range, the oil temp readings only fluctuated (rapidly bouncing around) by about 1 degree. At higher power settings as the oil temp got into the 190's, the magnitude of the fluctuations increased to about 3 degrees. Towards the end of the previous flight early last week when the oil temp got over 200, that's when i started seeing the oscillations of up to 6 degrees.
All other readings (incl CHT and EGT on all 4 cyls) are solid with no significant oscillations).

[Paul K]

I think I am having a failure as well but my temps bounce around at over a 150 degree swing! I'm apart for annual and plan to check all the wires tonight and check ground against the case and fuse to see if that is an issue. Rather "alarming" during flight, sets off the EFIS alarms constantly!

[Andy Hill]

An issue can be a "single wire" sensor that uses the Engine Earth(s) for the return path. If these are not perfect, the Alternator Load / noise etc. can influence the tiny Oil T signals.

Clearly the best solution would be to sort out the Earth problem, if there is one. We confirmed it by turning off the alternator, and the Oil T erratic readings stabilised. But could not find the issue...

Solved it by changing to a 2 wire Oil T probe - from GRT. Either run the second wire to airframe earth, or even right to the EFIS / Instrument.