A coolant temperature sender is an on engine protection device that is used to monitor the coolant temperature of the engine. Normally screwed into the engine block, it can output a range of values based on the oil pressure in the engine.
Where is the temperature sending unit located?
Most of the time it is close to the thermostat of the cooling system, or in some cases even inside of it. Note: Some engines may actually have a pair of sensors—one sending information from the engine to the control unit, the other sending information from the control unit to the dash.