Sensor, Oil Temperature. Sensor, Water Temperature (For E.F.I.).
Engine Coolant Temperature Sensor - Repair or ReplaceIf your engine coolant temperature sensor has failed, you may notice one of several symptoms: your temperature gauge doesn’t move, your engine overheats without warning, your radiator fans don’t switch on, or they don’t switch off. If your 1991 Toyota 4Runner has any of these symptoms, it's a good idea to let a trained Toyota technician perform an inspection.