Shelby:
I think 165 degrees F is too cool for operating oil temperature – don’t you need 180+ to evaporate the condensation?
Editor:
165 degrees F oil temp is the minimum recommended by Lycoming, though you will see the numbers 165, 180, and 185 at different places in various Lycoming texts. The quote from Reprints is “The desired oil temperature range for Lycoming engines is from 165 degrees to 220 degrees F”. Many or most engine people consider a minimum of 180 degrees to be much better, both for engine operation and to dry the oil. Water cooled automotive engines went from 165 to 180 on thermostats roughly 45 years ago; it was found that 180 reduced corrosion and obtained better cylinder sealing. Current auto engines typically run in the 200 range, as it has been found to improve engine life and performance.
Most Lyc oil temp thermostatic valves are marked with 180 or 185 degrees as the opening temperature. Normal “high cruise” oil temps should run between 180 and 200 degrees (my opinion). The dot in the green of most of our factory gauges represents 190 degrees, when the gauge is working right. Beech marked the 190 degree point because it is both normal and desirable. And now that I have said all this, the indicated oil temp will vary depending on where the probe is placed on the engine. Each gauge manufacturer provides a probe placement recommendation, from what I have seen so far.