05-17-2018, 01:18 PM
Alright, I heard from a master guru and want to add to the thread.
1. In most cases we have two speed fan motors. Those speeds are 1) fast and 2) slow & off. Since we are talking about a hydraulic motor, we have to think about the viscosity of the oil. So...when the oil is cold, the motor may not turn at all...as the oil heats up the fan will start turning slowly.
2) The AC compressor idea was probably a red herring and was just coincidence.
So....Lesson Learned: The radiator fan is controlled by a hydraulic motor that has two speeds. It normally runs at the slow / off speed until the engine tells it to turn to the high speed. Once it does its thing and cools off the engine, it returns to the slow / off speed. This model matches up with everything I experienced (except for the fan not running after driving on hot day). The system is incredibly simple.
1. In most cases we have two speed fan motors. Those speeds are 1) fast and 2) slow & off. Since we are talking about a hydraulic motor, we have to think about the viscosity of the oil. So...when the oil is cold, the motor may not turn at all...as the oil heats up the fan will start turning slowly.
2) The AC compressor idea was probably a red herring and was just coincidence.
So....Lesson Learned: The radiator fan is controlled by a hydraulic motor that has two speeds. It normally runs at the slow / off speed until the engine tells it to turn to the high speed. Once it does its thing and cools off the engine, it returns to the slow / off speed. This model matches up with everything I experienced (except for the fan not running after driving on hot day). The system is incredibly simple.
Bill Johnson
Birmingham, Alabama