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danbenua
07-05-2011, 03:37 PM
On flights yesterday I noticed the oil temp reading on my AFS-4500 jumping
around in a 20 degree range. I have not noticed this on previous flights and
typically see much more stable readings.

The following graph shows the oil temp over the complete 80 minute flight with
1 second sampling.


http://i985.photobucket.com/albums/ae335/danbenua/OilTemp_80min.png

This graph zooms in on a randomly selected 1 minute segment of the flight.

http://i985.photobucket.com/albums/ae335/danbenua/OilTemp_1min.png

Any ideas what could be causing this? I've ruled-out a loose connection at the sensor.
Thanks,
- Dan

Trevor Conroy
07-05-2011, 05:03 PM
Dan,
This is very typical of a bad ground somewhere in your system. The engine case (and 90 degree oil filter adapter if you have one), DC power bus, and EFIS case needs to be grounded REALLY well.

danbenua
07-07-2011, 10:33 PM
Good call Trevor. I added a ground wire to my oil filter adapter and the problem is gone.

It is interesting that it worked fine for 280 hours before developing the problem. I suspect
dissimilar metal corrosion added a small resistance somewhere in the ground path. The
problem might also have been fixed by just re-torqing the bolts securing the engine
ground strap and oil filter adapter. I did this as part of the ground wire installation
so I can't say which action actually corrected the issue. Here is a vote in favor of
making the two-wire oil temp sensor standard equipment in your sensor kit.
- Dan

Trevor Conroy
07-11-2011, 09:40 AM
Glad to hear it was resolved Dan. To keep costs down, we haven't made the 2-wire sensor standard as most customers don't require it. It does reduce labor though for builders.