Although I have moved on to the world of Subaru conversions, I remember
the oil temperature of my 2.1 L waterboxer was sensitive to oil level.  By
running the oil level at 25% above the bottom mark of the operating range
the temperature was much lower at interstate speeds than if the level was
at the top of the operating range.  I don't have temperature specifics
close at hand but I reported this to the List back in the 1990s.

Also keeping an internally clean radiator was necessary for stable overall
cooling.

Very impressive, Dennis.

Ed

344,000 miles on my 1986 Subaru powered Westy