I was out looking at one of our pusher buses and checking it out for running cold. The ambient temperature at the time was around -16 Celsius. In the video the first thing to check on these pusher buses is the hydraulic drive engine fan. The have stuck on in the past because of the either the boost temperature sensor (most common failure) or the coolant temperature sensor.
The bus is a 2000 Thomas ER Saf T Liner with a Cummins ISC diesel engine. They all come with the Parker hydraulic fan drive systems which works off the hydraulic pump. The hydraulic pump supplies both the steering and the fan drive. The fan drive system is controlled by a module attached to the frame below the fan drive.
It takes information from the sensors to run the fan depending on engine temperature and boost temperature. Since a fully engaged fan reduces horsepower.. the less rpms it runs during engine warm up the better. This reduces warm up time and increases engine power.
The module can not be serviced so if the sensors check out OK it has to be replaced. This is the reality in the modular filled world of new technology. If you’ve had any experience with these systems and want to comment please feel free to do so.