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Sorry, it's the 2.5. I'm assuming it's 1.75, 1.4 seems too small.Assume it's a 98. What engine?
Looking up all engines they seem to be 1.43 to 1.75 inside diameter.
Right, it's a thermoswitch, not a sensor. It will trigger the fan to come on when the coolant in the lower hose gets hot, indicating that the radiator can no longer cool without more airflow.Well, I would not install a temp sensor on the lower hose, but you may have a different intention than I. The upper hose is generally the place where coolant temperature is monitored. The lower hose(return) would be a place to measure the efficiency of the radiator at heat rejection. Compare hot incoming to cooled out-going and get the delta-T to know, given fluid flow(pump rpm), and ambient temperature to know radiator function.
Most electric fans use coolant temperature measured in the head or block, or an external add-on sensor(thermistor) taped to the upper hose to regulate cooling fan operation. Smart systems also use vehicle velocity, cutting off the fans above ~35mph.
If you are adding MORE cooling with this electric fan, then monitoring return flow may make sense, if the current, existing fan system is operable and left intact. The lower temp could be used to monitor when the existing is not getting the job done to your satisfaction.
tom