The Mazda 626 was equipped with several different engines, but all engines were equipped with an electronic temperature gauge. The gauge reads the signal produced by a coolant temperature sensor within the engine. When the sensor is defective, it simply stops working rather than slowly losing its accuracy. Fortunately, replacing the sensor in a 626 is a straightforward task.
Remove the radiator cap from the passenger’s side of the top of the radiator after allowing the engine to cool.
Open the radiator draincock at the bottom of the radiator with a wrench and allow it to drain, then close the draincock.
Locate the temperature sensor on the top of the water outlet. The water outlet is located on the top of the engine, on the end of the cylinder head.
Pull the single wire located on the tip of the sensor off the sensor.
Rotate the sensor in a counterclockwise direction with a wrench until the sensor detaches from the water outlet.
Count the first three threads on the replacement sensor’s threaded rod starting from the bottom of the rod to find the gasket sealant’s application area. Gasket sealant must not be applied to the bottom three threads.
Apply gasket sealant to the application area of the replacement sensor.
Rotate the sensor in a clockwise direction with a wrench until the sensor is secured to the water outlet.
Plug the sensor’s single wire into the tip of the sensor.
Refill the radiator with a 50/50 mixture of water and ethylene glycol antifreeze that is labeled as safe to use with aluminum radiators, then tighten the radiator cap onto the radiator.
