After 8 weeks of no flying due to modifications, weather and scheduling we flew again on Saturday even though it was about -2F at take-off … oil temp got as high as 210F on climb out and water was about 170F when we leveled off at 2000’ ASL … as we circled for about 7-8 minutes (5500 rpm) on the upwind side, the water temp and oil temp kept dropping; we were alarmed by the also steady reduction in coolant pressure from 11 PSI down to 6 PSI and the water temp down to about 120F … having never seen this before we decided to land and check for leaks … there were no leaks in either coolant or oil.  I called Tracy Crook, he didn’t think anything unusual was happening, except that the oil cooling needs to be improved (I agree) and that a 5-10 minute period of stabilization is normal.

 

Further … for our previous flights, the expansion tank was holding from 10-15psi before engine start … on Saturday, the tank was only 2-3psi before engine start.  I think what happened was the engine heat increased the pressure from 3psi to 11psi during climb-out but after we leveled off and reduced throttle the combined reduction in power and increased cooling air flow simply cooled the engine significantly. The reduction in coolant temperature resulted in decreased pressure and the oil temperature followed for the same reasons. I don’t know how low the oil temp went as I was fixated on the coolant pressure.

 

It appears that adding the second air purge line from the rear iron to the top of the expansion tank has changed the cooling system pressures

dramatically. Previously there was one purge line from the high point in the water pump outlet to the bottom of the expansion tank … with this setup, the system would pressurize to the cap pressure and stay there no matter what.

 

Am I getting fooled here because the system was not pre-pressurized?

Or are the temps just so low that I’m in unknown territory?

Jeff