JUst as a point of information on some data that I do know, I observed my bus engine thermostat operate on a return trip from New Orleans this spring.

My thermostatic fan clutch had acted up so I had locked the fan. Prior to that my fan clutch controlled engine coolant temps and the temps would cycle between 200 and 205 as indicated on the gauge.. With only the engine thermostat to control engine temps the engine cycled between 190 and 195 as indicated by the gauge.

For the entire trip, including those portions where the bus was pulling hills and was operating at max power the thermostat cycled open and closed. This was consistent with the operation when the fan clutch was working normal, although the cycle temps when using the fan clutch were between 200 degrees indicated which I assume was when the fan clutch disengaged, and 210 under hill climb conditions which was when both clutch speeds were engaged. My point is that as long as a fan is fully engaged an engine is likely to cycle its engine coolant flow via the thermostat. With the thermostat removed as in Tuga's coach I would have expected to see temperatures in the 140 to 160 range at the radiator inlet side and lower at the suction side.

The reason I suggest they should be this low is because the cooling system is working with a generator that is lightly loaded and the system design should be capable of handling excessive ambient temps under full or heavy loads. I am having a problem agreeing with John on the 10 degree temperature drop, but until I can determine that is typical I have to accept his word because I doubt if any one else in the Prevost universe has a better understanding of the transfer of heat.