Reference the question above on optimum diesel engine operating temperature, at one time I worked for a public transit system and had the job of researching technical information and writing the specifications for new equipment purchases. At that time, 195 degrees was the optimum operating temperature for a diesel engine, since the laws of physics do not change that temperature should still be optimum - thus the recommendation by the Cat technician. We purchased thermostats, cooling system components including radiator shutters in order to maintain 195 degrees as consistently as possible.