So here are the facts:

1) My engine is back together and the plane is flying again

2) The only parts replaced were CHT probes, seals, gaskets and overflow bottle.

3) Compression is 86,86,86,85
4) Full root cause is still not fully known.

Between myself and my Rotax guru A&P we have a probable cause:

1) A near gross load reduced climb & cooling performance allowing for increases in coolant and oil temps.

2) The radiator and oil cooler had been taped for several months for the cold temps.

3) It was a warmer day (50s), This combined with the higher fluid temps to increase the effective EGTs.

4) Higher EGTs created a small hole in the overflow bottle allowing the coolant to evacuate from the overflow bottle. The failure point was closest to the exhaust pipe.

5) As the engine warmed and then cooled between climb out and initial cruise, the engine attempted to draw coolant from the overflow bottle.

6) Air introduced into the system created an airlock.

7) The airlock pushed the remaining coolant out of the system through the now failed bottle.

8) Detection of the event by smell resulted in an immediate turn back, descent and reduction in power.

9) The cowling provided adequate airflow to prevent a full over-heat event during the descent.

As a result I have changed to a thicker, heat resistant bottle for the overflow reservoir. The bottle has also been heat shield protected and raised to distance it from the exhaust.

My plane had 175 hours on it at the time of failure, so no warranty was in effect.

Falcon Insurance did cover some of the costs for the tear down inspection under the clause that pays out when the pilot takes reasonable actions to prevent further loss.