So after 11 years and ~840 hrs of flying my oil temperature is going crazy. It measures ~ambient temperature at start and then as the engine warms so does the oil - ok that's normal but the temperature just keeps going up and the last couple of flights it's gone off-scale high (160+degC). All other sensors, i.e. oil pressure, EGTs, CHTs, etc, remain normal. Reviewing the data from the AF3500EM I see the temps did start trending up late last year, but nothing like what they are now

My last task before shutting the engine down is a mag. check, and before that I shut everything else down with the alternator being the last item turned off. At the end of my last two flights I've noticed that when I turning the alternator off the oil temperature returns to normal, which makes me think I have an alternator problem however an avionics engineer has suggested it's more likely to be an oil temp. sensor problem than the alternator.

We've tested the oil system and everything's fine there, ditto the temp. sensor and vernatherm have been tested and we believe are operating normally.

Other posts on this forum imply I should replace the sensor with a 2-wire model, and also that what I have may be a standard automotive sensor (it came with the sensor pack I purchased in 2007 if that helps).

I'm happy to replace the sensor, but then I'd need calibration numbers etc

Your thoughts and guidance would be appreciated