Todd,

 

    It might not be too surprising about the oil temp varying as it does.  The key as you mentioned is the power load.  Here's my thinking.  Since the oil is the primary cooling medium for the rotors where the power is produced, it would seem to me that a rise in temperature (due to a power increase) would first be localized to and  noticed in the oil -  before some of the increased heat perhaps diffused over to the coolant system.  Thus a surge in oil temperature as the power increases may well result in a larger temperature drop until it reaches thermal equilibrium again. 

 

 If the cooling part of my spreadsheet is anywhere close to reality, it shows that the Mazda oil cooler is actually not rejecting sufficient heat at certain power settings and airspeeds.  Indeed, of the evaporator cores and oil cooler, it appears the cores support getting rid of some of the heat the oil cooler apparently does not reject under certain operating conditions.  This again implies (at least to me)  that you might see a surge in oil temps before the increased heat from the oil diffuses over into the coolant system and stabilizes temps..

 

Someplace I read that when a cooling system is operating at its greatest Delta T, it is not only operating at its most efficient it is also operating on the verge of cooling failure {:>).  In that by definition, the greatest Delta T means the temperature difference has stabilized and only the mass flow now has any affect on heat removed.  If Temperature of incoming medium continues to increase pass this point and  results in no further delta T difference, that means the additional heat is not being completely rejected.  Only alternative in that case to get rid of the additional heat is to increase mass flow.

 

Ok, that has exposed my ignorance about heat transfer - Bill? anybody else have a theory?

 

Ed Anderson

 

 

    I don't have a OAT sensor on my plane but the ground temp was 9C. I took it up to 13000, where it should have been ~ -17C. Oddly enough I seem to have a constant 20C delta T on the coolant but the oil delta T will vary between 5 and 20 degrees depending on power load. 

 

SNIP

 

. This indicates (to me) possible localized boiling in the block for a few seconds until the flow increases again, reducing the pressure. For this reason I've taken to switching the pump to bypass the controller while practicing touch & goes.