Fresh rebuild, two hrs. of test run time, coolant in combustion chamber from-?, confirmed with exhaust removal and borescope. During rebuild irons were inspected, resurfaced and surface rehardened. Thoughts at this point: I messed up and pinched a seal ( 35 years professional automotive repair, automatic trans, computer controlled sys. specialist, was very meticulous about housing mating ) or cracked rotor housing, was seeing coolant coming from bottom of exhaust at housing after run. Any other thoughts welcome. Removing eng., again, now.                                  David R. Cook  RV6A Rotary.