Simply determining radiator coolant delta T may be useful in troubleshooting the cooling system.  The water cooling system is a closed system with two heat exchangers: one is the engine putting heat into the coolant and the other is the radiator removing heat from the coolant.  When all of the coolant flows through the engine and radiator (coolant bypass passage blocked by either a plug or a fully open thermostat) the engine and radiator must have the same coolant delta T.  At a given power level and coolant flow rate we all should see similar delta T's since we are using very similar engines.  At sea level full throttle, that coolant delta T should be close to 15 degrees F.  Since the heat exchanger characteristics of a clean engine are essentially fixed, a coolant delta T of much more than15 degrees F at full throttle would most likely be a result of insufficient coolant flow rate through the system.  This could result from a defective water pump or too much coolant bypassing the radiator such as due to an incompletely closed thermostat bypass passage, too large air bleeds from engine coolant high points, or an open cabin heater coolant loop.  An EWP would introduce an additional variable.  

With proper coolant flow rate, when the radiator cannot remove enough heat from the system, the overall coolant temperature will rise until one of two conditions are achieved.  First, the radiator may be capable of removing enough heat with a greater delta T between the coolant and the air.   The system will stabilize, but the delta T's of the coolant across the engine and across the radiator will remain essentially equal and unchanged.  This type of behavior is demonstrated in the attached data plot for a full throttle climb from 7,000 to 14,0000 ft msl with a typical OAT decrease.

The second condition would be to boil the coolant and remove heat due to the phase change.  This may not maintain a closed system and the stable condition would then, of course, be temporary.

The goal of designing the radiator side of the cooling system is to size the radiator and air flow through its core to achieve the desired overall coolant temperature.  Trying to change the coolant delta T at a given RPM and power level will prove frustrating.

The same would be true of the oil cooling system if the oil flow rate was consistent between our systems.  However, if part of the oil flow is returned to the sump at the front cover relief valve, comparisons between different setups will be of limited value unless the actual oil flow rates through the oil coolers are known.  

Steve Boese