oil temp fluctuation

[dynonsupport]

Bad grounding usually causes temps to go higher than they are. Temps going lower than they are sound like a loose wire or connection somewhere.

 

[dodsond]

I put in a UMA 1B3 oil temp probe and the fluctuations have stopped.  It is rock steady now.

Now though, oil temp indicates 100 degrees F as a minimum.  Do I have a problem or is there something that can be done to lower the minimum indication? 50F would be far more useful and 30F would be my desire.

On a related note, the CHT fluctuation I reported back in September was fixed.  I better secured the wire bundle as it jumped from the engine to the airframe.  There was about 12" unsupported length that also contained the connectors.  It was a stiff bundle with spiral wrap to help support it, but I tied it to a large SCAT hose nearby.  That may have been the issue but more likely is a misrouted ignition wire.  That wire got against the exhaust and the insulation was compromised.  I have Lightspeed systems that have silicone wires and very high discharge voltages.  The spark was fine but I suspect the CHT wire only a fraction of an inch away from that burn was getting EMI.

 

[dynonsupport]

dodsond:

Did you try adjusting the displayed ranges?

EMS SETUP > SENSOR > OIL TEMP

Adjust the ranges from the bottom up. Likely you'll see that the BOTTOM YEL is set to 100, so adjust that per your preference.

Note that if you have a ROTAX engine, and have set engine type to ROTAX, oil temp ranges aren't adjustable per Rotax specification.

I put in a UMA 1B3 oil temp probe and the fluctuations have stopped.  It is rock steady now.

Now though, oil temp indicates 100 degrees F as a minimum.  Do I have a problem or is there something that can be done to lower the minimum indication? 50F would be far more useful and 30F would be my desire.

On a related note, the CHT fluctuation I reported back in September was fixed.  I better secured the wire bundle as it jumped from the engine to the airframe.  There was about 12" unsupported length that also contained the connectors.  It was a stiff bundle with spiral wrap to help support it, but I tied it to a large SCAT hose nearby.  That may have been the issue but more likely is a misrouted ignition wire.  That wire got against the exhaust and the insulation was compromised.  I have Lightspeed systems that have silicone wires and very high discharge voltages.  The spark was fine but I suspect the CHT wire only a fraction of an inch away from that burn was getting EMI.

 

[dynonsupport]

Doug,

Did you change the setting to use the UMA sensor instead of the Dynon one? I am guessing that you still have it set for the Dynon, which has a different calibration, and what used to be room temperature now looks like 100 degrees. This means all your temperatures are off. Note that sensors are not linear, so it may be of 30 degrees at room temp but only 6 degrees at hot, so you may not be able to notice.

There's nothing in the code or calibration that limits the UMA to 100 degrees, so something else is up.

 

[dodsond]

I set sensor type to 10 in the setup and have v5.5.0 software. The bottom of the yellow arc is 80 and green 90. In the past that only affected the analog display. The digital display showed ambient no matter how cold prior to start. Right now oil temp is 98 but CHT, EGT, OAT are all showing right at 80.

This is a Lycoming engine in a Glasair.

 

[dynonsupport]

Where is the negative lead of the UMA grounded?

 

[dodsond]

It is spliced with a lead I strapped to the body of the 1 wire oil pressure sender.  That wire goes to a metal panel on the firewall which itself is grounded with a large gauge wire to a brass ground buss in the cockpit.  The D-120 case is grounded to that buss and so is pin 3 with a separate wire.

All of the senders have worked well but oil temperature.  I had strapped a ground wire to the body of the Dynon sender but that didn't affect the fluctuation.  This UMA sender seems very accurate and stable once the temps are above 100, but displays between 98 and 101 until then.

 

[dynonsupport]

The wire for the UMA needs to go direct to one of the grounds on the EMS, with no splices to other grounds. What you have there means the UMA is grounded to the engine block just like the old one was, because the ground wire it is sharing with the oil pressure sender causes the ground to be the engine ground.

 

[dodsond]

Well, true and not true.  The oil pressure sender is not directly mounted to the engine, there is a hose.  That is why I strapped a wire to the body of the pressure sender and ran that to the firewall ground. This is also the manner in which I grounded the fuel pressure sender. Of course, the engine itself is also grounded with a braid to the firewall ground.  All three go to a single point on the firewall ground.

The firewall ground is connected to the fuselage ground buss with a big ol' 6ga wire.

There are not enough pins in the D120 to send everything to it on separate wires so splices or a buss is necessary.  Also the probe leads aren't long enough either.

Why would the sensor grounds all be solid but this one?  Why is oil temp (two different probes with two different symptoms) the only bad actor?

I am convinced the UMA probe is accurate above 100 degrees and will test it the next chance I get.

 

[dodsond]

Here is some more information. The colder the ambient temperature is below 98 degrees F, the higher the oil temperature reads at engine start. After engine start, the indicated oil temperature drops predictably, degree by degree as the oil warms up. It drops consistently to 98 or 99 degrees F. It stays at 99 for a minute or so then starts to rise.

During flight, the temperature indicates what I would expect based on previous experience to include extended periods between 170 and 180 since that is the set point for the oil cooler bypass.

The readings are repeatable and very stable. This really doesn't sound like a grounding problem but I haven't had a chance to test the probe or try a different ground. If is isn't the calibration software, then could it be a malfunctioning sensor?

 

[Dynon]

At ambient, with the engine off, what does the temperature read? Can you measure the voltage when it's powered on at ambient (and report the temperature that you're seeing)?

 

[dodsond]

I checked this out for several days.  The scale is repeatable.  I used CHT for the ambient temperatures:

ambient (CHT)    oil temp (indicated)

58 109
64                      105
66                      104
68                      103
70                      102
75                      100
77                        99
78                        99
80                        98

The bus voltage as reported by my EFIS was 12.3.  For some reason the EMS has always reported the voltage about .5 volts lower all the time and this was no exception.

I haven't had a chance to pull the cowling and put the probe in boiling water and ice water which should be a decent two point calibration check.

Doug Dodson
Glasair II-S FT, Lycoming IO-360, UMA 1B3 (Type 10) probe

 

[Dynon]

Hmm, not quite making sense. To help your troubleshooting, here's what you be able to measure at the sensor (resistance when powered off, voltage when powered on)

temp(f) ohms voltage
100 2916 3.72V
140 1232 2.75V
180 592 1.85V
220 303 1.16V
260 170 .72V
300 101 .45V

 

[dodsond]

Do you have those numbers between 32F and 100F?

 

[Dynon]

I knew you were going to ask that. The data I have immediate access to doesn't have those values, unfortunately.

 

[dodsond]

I got these numbers from UMA. I don't understand the source of voltage numbers you gave but the sensor is a simple thermistor. The same info is available from the spec sheet on Digi-Key for the off-the-shelf thermistor UMA uses.

Temp (F) Ohms
30 17364
40 13108
50 9990
60 7679
70 5950
80 4646
90 3654

I attached the file they sent me. The numbers there are very slightly different than what you sent above, but that can be simply due to conversion from C to F or the method of interpolation.

UMA is sure the symptoms I have aren't' a probe failure. Reversing signs on the calibration slope doesn't seem possible with a thermistor I won't get a chance to pull my cowling and check the probe for a few days but I am still baffled how anything about my installation can cause the slope change regardless of whether or not the engine is running.