I've told by another well respected rotary expert that the REW is designed
to run at 203 - 212F, that oil temp should be kept below 240F, and should
never regularly go over 248F. Everywhere I go I hear different numbers for
these limits. I'm using 5-30 Castrol Synthetic.


The 160 degree oil temp idea comes from how much power you start losing as the rotor face gets hotter. There is no doubt that it is possible to be showing higher oil temperature and still have rotor bearings survive. Keep in mind that some of the oil in the "wedge" on the bearing face will be leaving the bearing at a much higher temperatures than what you see on the gage. Not all of the oil that goes across the bearing gets all that hot. Another point is that with a hard pull at full throttle the rotor cooling oil may get very hot very quick. So, there are several things to think about here.

With a sensor bulb in the pan, you get a collection of temperature reports over a short time period based on where the throttle is set. Over a longer period, more closely related to how much heat rejection your oil cooling system can perform.

The primary object of cooling the oil is to prevent the movement of the bearing overlay. The soft shiny stuff that turns up in the filter when things go wrong. An amount of added capacity beyond that to account for Murphy adjusting something the wrong way while you look at the chart.   A stable oil temp at cruise on a hot day might be a more realistic objective. So a climb at lower angle or short of full throttle (like big airplanes) is no sin, (trading climb angle for air speed across the coolers) Or running a way richer climb power. So long as hot day WOT at 8,000 feet cruise can be performed with oil temps stable at (fill in your oil temp here). In the end, it is the WOT cruise setting that is the gold standard of performance. Getting there is all the fun. I have temp bulbs in the tank (pan) and the line to the rear main bearing.

Lynn E. Hanover