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intermittent oil temp on G3X

D

Desert Rat

Well Known Member
I've had the oil temp gauge on my G3X red X a couple of times now.

The first time it happened was during a static run. The data file shows it X'ed out at 129 degrees. After I rolled it back into the hangar I powered back up and it was displaying normally. Due to the intermittent nature, I thought I probably had a bad crimp where I hooked the probe up to ships wiring FWF, so I replaced those spade connectors with D-sub pins in heat shrink and that seemed to cure the issue.

A couple of subsequent short engine runs to adjust stuff, including a full power static run to look at the prop pitch, no problems.

On my first flight, it red X'ed again, this time at 131 degrees and stayed off for the duration. 20 minutes or so after shutdown I turned the master on and it was up and displaying about 190 degrees, as one would expect.

Yesterday I verified the configuration was set for the right probe (UMA 1B3-2.5R) and that my gauge temp parameters were reasonably wide (40 degrees to 250 degrees).

Since that all looked good, I pulled the connector off the GEA24 and looked for a pushed back or badly crimped pin, but all appears good on that end as well.

At this point, it seems like the only thing it could be is either a broken/shorted wire deep in the guts of my EIS wire bundle or a bad probe.

Unless I magically fixed this by un-pinning/re-pinning the GEA24 connector, my next step would seem to be putting the probe in a pot of hot water and seeing if the resistance increases in a linear fashion as it heats up or if it suddenly gets screwy at some point.

So, after all this back story, I've got a couple of simple questions:
-has anybody had one of these probes fail out of the box? maybe with similar symptoms?
-is there any other likely cause for my symptoms that I haven't considered?
 
I've had very similar issues with a MAP sensor in a g3x setup. On my third sensor now with identical indications and red X's. I'm betting it's not your sensor.
 
Desert Rat said:
I've had the oil temp gauge on my G3X red X a couple of times now.

The first time it happened was during a static run. The data file shows it X'ed out at 129 degrees. After I rolled it back into the hangar I powered back up and it was displaying normally. Due to the intermittent nature, I thought I probably had a bad crimp where I hooked the probe up to ships wiring FWF, so I replaced those spade connectors with D-sub pins in heat shrink and that seemed to cure the issue.

A couple of subsequent short engine runs to adjust stuff, including a full power static run to look at the prop pitch, no problems.

On my first flight, it red X'ed again, this time at 131 degrees and stayed off for the duration. 20 minutes or so after shutdown I turned the master on and it was up and displaying about 190 degrees, as one would expect.

Yesterday I verified the configuration was set for the right probe (UMA 1B3-2.5R) and that my gauge temp parameters were reasonably wide (40 degrees to 250 degrees).

Since that all looked good, I pulled the connector off the GEA24 and looked for a pushed back or badly crimped pin, but all appears good on that end as well.

At this point, it seems like the only thing it could be is either a broken/shorted wire deep in the guts of my EIS wire bundle or a bad probe.

Unless I magically fixed this by un-pinning/re-pinning the GEA24 connector, my next step would seem to be putting the probe in a pot of hot water and seeing if the resistance increases in a linear fashion as it heats up or if it suddenly gets screwy at some point.

So, after all this back story, I've got a couple of simple questions:
-has anybody had one of these probes fail out of the box? maybe with similar symptoms?
-is there any other likely cause for my symptoms that I haven't considered?
Click to expand...
I had the same problem returning home from OSH last year. It ended up as a bad connection where the oil temp transducer connects to the GEA 24 harness forward of the firewall. Note - this was 300 hours after G3X installation.
 
Steve said:
I had the same problem returning home from OSH last year. It ended up as a bad connection where the oil temp transducer connects to the GEA 24 harness forward of the firewall. Note - this was 300 hours after G3X installation.
Click to expand...
That was the first thing I checked. It seemed like the low hanging fruit to replace those connectors, but no joy there :(. That does help me though, to know that the symptoms seem to fit a bad connector issue.
 
I have had a similar problem over the past year. I‘ve recrimped the connection at the probe a couple times which seemed to fix it for a bit. But the problem returned.

I recently replaced the sensor and attached it to the harness with butt splices. We’ll see if that addresses it. The airplane is currently down while I replace the crankshaft seal which was rotating easily on a 1 year old Thunderbolt!! Dodged a bullet on that having just returned from round trip from Portland, Or to Myrtle Beach, SC.
 
For grins/giggles - install a temporary, new wire between the OT probe and the GEA 24; if it still Red-X’s then swap out the sensor - if that doesn’t fix it, then swap the GEA 24.
 
My experience has been that the oil temp sensor is the most sensitive to a very good connection. I had this issue and I changed the spade connection multiple times and with real good crimp only to show itself again. I finally changed the type of connection from a spade push in type connector and have never seen the issue again.
 
Bavafa said:
My experience has been that the oil temp sensor is the most sensitive to a very good connection. I had this issue and I changed the spade connection multiple times and with real good crimp only to show itself again. I finally changed the type of connection from a spade push in type connector and have never seen the issue again.
Click to expand...
What sort of connectors did you change to? I originally had spade connectors, but after the first time I changed to D-sub pins in heat shrink, but here we are again. If there's a better connector than D-subs I'm all ears.
 
Desert Rat said:
What sort of connectors did you change to? I originally had spade connectors, but after the first time I changed to D-sub pins in heat shrink, but here we are again. If there's a better connector than D-subs I'm all ears.
Click to expand...
I used this type of butt splice connector.
racespeconline.com

Raychem Mini-Seal Butt Splices

Ensure strong connections with Raychem butt splices, crafted for automotive reliability. These mini-seal splices are perfect for demanding applications.
racespeconline.com racespeconline.com
 
I wanted to circle back to this with the resolution in case somebody has the same issue in the future and comes across this thread.

Some research revealed that the UMA 1B3-2.5R should have 100 ohms resistance at zero degrees celsius with resistance increasing 0.38505 ohms for every one degree celsius temperature increase.

I pulled the original probe out and checked it in a pot of water on the kitchen stove with candy thermometer. I also had an ohm meter hooked up to it.

On the first attempt, as the temp increased, the correlation between ohms and temp was linear and within a degree or two of expected all the way up to about 215 f. I shut the stove off and it tracked appropriately on the way back down as well. On the second attempt, at about 140 degrees indicated, the resistance shot up to a reading that correlated to about 500 degrees f.

I did the test series twice more but was unable to duplicate the fault. My assumption is that something isn't quite right where the wires are potted inside the probe, but thats just a guess on my part.

I replaced the probe with a new one and now have about 6 hours on the plane with no further faults. Fingers crossed that this particular gremlin has departed the pattern.
 
One other thing I did out of an abundance of caution was to put a blob of RTV on top of the probe where the wires exit to hopefully provide a bit more strain relief.
 
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