Paul,
           Do I run a thermostat in the renesis  or not?  What is the
current thinking.  I do have an oversize heat exchanger, so in winter it
may well be needed?

Neil.

It is coincidental that you bring that up right now. Mike's RV4 has a thermostat.

In theory you don't want to control engine temperature with a thermostat.
It is better to control engine temperature with cowl flaps as they
better match the cooling requirements of an aircraft. On climb out
where drag is not important open cowl flaps can greatly improve
the cooling performance. At cruise cooling performance is less of
an issue and closing the cowl flaps can drastically reduce the drag.
In my C82 it is worth 3 MPH at 150.

Now Mazda uses a by pass thermostat built into all water pumps  prior
to the RX8. What that means is the thermostat is double acting. When
the engine is cold one valve in the thermostat closes access to
the radiator and opens a by pass passage in the water pump.
That re-circulates the water in the engine promoting rapid warm
up for smog reasons. Not necessary in an aircraft engine.
It will get warm just taxiing to the runway.

In the past I modify the stock pump to close off the bypass passage
and do away with the thermostat. That increased the rate of water
flow through the system and cools the rotor housings better.
The faster the water flow the better the cooling. Here are some pictures
of that modification. DO NOT merely remove the thermostat. The by pass
passage will still be there causing your engine to over heat.

The RX8 fortunately has improved the water flow through the engine and
mounted the bypass thermostat in an external housing. Just do away
with that thermostat housing, plumb the water pump directly to the
rad and you are ready to fly.

Paul Lamar

Paul,

I love all these email updates! Soo much good info! Would u recommend that waterpump mod on street driven rotaries? (w/track day wknds?) I plan to make a bridge-ported 12a...

Dan Corsine

Not worth it on a street rotary, Average power is only 40 HP or so
while an airplane is well over 150HP.
More important ot warm it up fast.


Paul Lamar