I met the design engineer working on this Elbit Systems UAV
engine at the Paris air show. It is a two cycle four cylinder
engine with a reed valve intake system. His goal is a BSFC
of .45. That would be excellent for a 2 cycle engine as they
are generally over .6 BSFC. He told me he is experimenting with
motorcycle fork oil as a cooling fluid. The idea here is to
raise the engine operating temperature to reduce the
heat loss to the cooling system and allow smaller, consequently lower
aerodynamic drag heat exchangers. Oil generally boils at a higher
temperature  but the heat transfer rate from oil to metal
is generally not as good as water or water/ethylene glycol mix.
Low viscosity helps and that is one reason Mazda recommends
5W30 oil for the RX8 engine. Cools the rotor and bearings better.
Idemitsu is importing 5W30 rotary engine oil. Available from
your local Mazda rotary hop up shop.

If you care to experiment with oil cooling I would instrument
the rotor housing with at least one thermal couple close to the
lower spark plug within about 1 mm of the combustion chamber. That
is the hottest point in the engine. The heat exchanger must
be of the oil to air type, such as the stock Mazda oil cooler,
as they generally have internal tube fins that enhance the rate of
heat transfer from oil to metal.

Paul Lamar