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Dorsal
12-30-2011, 03:44 PM
So I was out flying today, nice day nice flight and towards the end my oil temps climbed first into the yellow then red and where a bit erratic. I landed, checked the crimp on the sensor lead, oil levels etc. Next flight the temps again went into the red as did the CHT though they where also erratic jumping by as much as 100 deg leading me to believe this is a sensor or grounding issue. I nursed my plane back home at 4000 rpm (relatively short hop), CHTs high normal and oil in the early red (all other indications and engine behavior where normal). Immediately after shut down (a few seconds) I read the temp of the oil filter (infrared) at 160 deg while the EMS still indicated 280, usually these are fairly close. I will head up in the morning to try and diagnose but though I would seek the wisdom of the board for others who may have had such an issue. My current thinking is that it is sensor related perhaps due to grounding. I certainly hope it is not an indication of a "real" problem though with the instability of the readings I think it is electrical (actual temps can't jump around much).
Thoughts?

kmach
12-30-2011, 07:44 PM
Hi,

Which Dynon are you using? I have the D-120 EMS . To me it sounds like you have a loose connection somewhere.
I have had a loose spade connector on a CHt that gave some strange readings , I would check all joins, connectors and as you mentioned the grounds .

Dorsal
12-30-2011, 07:52 PM
I have the EMS D10, will be checking connections tomorrow.

jdmcbean
12-30-2011, 10:39 PM
Dorsal
Check grounds... unlikely the connectors are loose on all 3 sensors...

I am assuming that the Oil Temp and both CHT were all reading erratic...

Was it happening only when transmitting ? I have seen the indications jump during transmition and then settling back down after..

Also, how are the resistors wired in ? are they sharing a common point ?

Dorsal
01-01-2012, 03:34 PM
Checked ground lug to engine, everything looked clean and tight. I cleaned it anyway and added a star washer, test flight all was good. Happy that the readings are good but would have preferred a smoking gun so I know I fixed it.

CDE2FLY
01-04-2012, 08:28 PM
Glad to hear you're back in the green. I've had an erratic read out on occasion with the GRT engine analyzer (oil/CHT temps) but only while holding the transmit button for the radio. I attribute it to some electrical noise between the engine analyzer and the radio. My guess is yours may be a ground issue as others have suggested. I noticed during the wiring process while building that incomplete grounds can spike both CHT and Oil temp readouts.

Dorsal
01-29-2012, 12:46 PM
Not so fast :mad: could really use some help here.
This post should have a graph of my oil temps over the course of 10 minutes (x axis in seconds) during a flight yesterday. The first leg of the flight the temps where 204 +- 1 degree @ ~5200 rpm. On the flight back I was running closer to 5400 rpm when I noticed the temps getting high. I throttled back to 5000 even for the remainder of the flight. The data shown is at least ten minutes after throttling back and all other conditions where held constant. Oil pressure and CHT all remained steady during the flight.

Current observations (please feel free to challenge)
1 This can't possibly be real as oil can't change temperature that fast.
2 Not likely a grounding issue as I just cleaned and added a star washer and no other readings were affected.

Has anyone else had fluctuating readings like this?
Has anyone ever had an oil temp sensor go bad?

Ideas, suggestions? :confused:

Esser
01-29-2012, 04:08 PM
Dorsal this may not be any help to you but oil does change temperatures very fast. Usually heats up quick and cools down a little slower. With my air cooled 600cc Honda motorcycle I have a digital oil temperature gauge in my dip stick. If I am on the throttle I can gain 25-50 degrees in as little as 10 seconds depending on the conditions. With an oil cooler it may oil down quite fast. Not saying this is related to your problem but I thought I would chime in my experience.

Dorsal
01-29-2012, 05:38 PM
Thanks for the input Esser, My concern is I am getting >10 deg in 1 second with no changes in throttle. Has to be electrical don't you think?

Esser
01-29-2012, 06:25 PM
Yeah, I would say faulty sensor or something. Is the oil sensor just one unit?

kmach
01-29-2012, 07:23 PM
Hi,
you could try swapping a CHT temp sensor and the oil temp sensor. This would confirm if it is a sensor fault.

Dorsal
02-26-2012, 04:01 PM
Well for those interested in this thread I believe I found and solved the problem. First it is important to note that the thermistor on the Rotax has a negative temperature coefficient which means the resistance goes down as temp goes up. This had me looking in the wrong place as any increase in resistance due to the sensor connector or the engine ground would result in artificially low temp reading not high. The problem turned out to be insufficient grounding of the EMS as it's normal power draw had the case (the EMS ground reference) 40 mV over Batt ground. This also likely allowed for electrical noise on the EMS ground causing the erratic readings. At any rate a hard 14 gauge grounding of the case and all appears quite happy! :D