Final answer:
The thermatic viscous fan hub nominally engages at 155°F (68°C), but due to heat transfer efficiency and radiator operations, minimum slip drive likely occurs at coolant temperatures around or above 95.0°C.
Step-by-step explanation:
The temperature rating of a thermatic viscous fan hub is nominally set at 155°F (68°C), indicating the point at which the fan will engage to cool the engine. However, due to various factors such as heat transfer efficiencies and engine operating conditions, the coolant temperature at which minimum slip drive occurs as temperatures rise will be higher than the fan hub's nominal rating.
Given that most car radiators operate at temperatures higher than 95.0°C, we can estimate that the minimum slip drive would be engaged at coolant temperatures somewhat above the fan hub’s nominal rating, potentially around or above 95.0°C, taking into account the efficiency of heat transfer from the coolant to the fan hub sensor.