The car overheats and loses coolant. Radiator passages are clear, there is good flow. Thermostat and waterpump have both been replaced. System has been pressure tested, no apparent leaks found. No coolant entering combustion chambers as verified by inspection of the spark plugs. Does anybody know how to test the hydraulic-actuated radiator fan? It appears to turn too slowly for sufficient airflow, the transmission fluid level is normal. Any information provided will be greatly appreciated.

How's the engine timing?
The fan should turn about 1100 rpm. It shouldn't affect your cooling during normal driving since it's not engine driven or connected to the water pump. It gets its fluids from the power steering unit. How's that look or sound? Your fan should either turn on or not and it sounds like it's turning. Any other symptoms?

I mention the engine timing because if it's advanced or retarded too far then the engine will overheat and can lose coolant. I've even seen the top of a radiator blow off because of it.
As for the fan, get the engine and the powersteering fluid warmed up and then let someone hold the accellerator around 2000 rpm while you check the powersteering reservoir. If it's foaming then bring the fluid level up to the HOT mark.