My 1996 Bluebird rear engine with the 8.3 Cummins has the
radiator and fan setting on the drivers side of the engine bay.
The fan is driven by hydraulic pressure from the power steering
pump. The fan is attached to the hydraulic fan motor and is
supplied with oil by two hoses. The temperature is controlled by
a temperature switch on the engine. If I remember correctly the
switch is electrical and controls a solenoid in the pressure line to
activate the fan at the proper time. Prior to my getting the bus
the state repair facility logged a similar complaint to what you
are describing with my bus (ie Using coolant and running hot).
After removing the head to check for head gasket failure they
found a cracked head which they subsequently repaired.