Newly certified kit built aircraft with a 914.  Engine time is only at a few hours.  Beginning ground tests and avionics calibration.

Today while trying to warm up the engine to 120 degrees it never got there after about 10 minutes.  Didn't seem right as it was about a 70 degree day.  Increased RPM to about 3000 and it still did not get warmer than 115.  Shut down and removed cowling and checked the oil -- it was certainly hot.  Checked sensor, unpluged and reseated it.  Powered up the EFIS and it read 181.  Did a few other things, adjusted prop pitch and went to test again.

Upon start temp was about 111 and rising fast.  As soon as I switched on the alternator, the temp dropped instantly to 60.  Shut off the alternator switch and back up it went.  So somehow the power generation is creating interference to the sensor or avionics.  In my installation, I do also have the external alternator.  Both the integrated generator and external alternator fields are connected to the same switch.  I believe that once the integrated generator comes alive it can't be switched off by breaking the field wire like you can with the external.  So this would lead me to the external causing interference somehow.  However, no other sensor changes readings -- only the oil temp.

Not sure of a ground issue as it does read ok with the alternator turned off.  Could the external alternator cause some type of interference to the sensor or a G3X component?  Should the wiring need to be separated away from the power lead?  Any ideas?

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