Buy OEM Lexus Part # 8342016040 (83420-16040, 8342020030). Engine Coolant Temperature Sender. Switch and relay and computer

GAGE ASSY, WATER TEMPERATURE SENDER

Fits GS 300, LX 450, SC 300

Engine Coolant Temperature Sending Unit - Repair or Replace
If your engine coolant temperature sender 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 Lexus has any of these symptoms, it's a good idea to let a trained Lexus technician perform an inspection.