1. Measure the temperature around the water temperature sensor.
2. Measure the resistance between terminals of the water temperature sensor.

Water temperature sensor removal/installation
Refrigerant pressure switch removal/installationMazda 6 Service Manual: Key Battery Replacement
If the buttons on the transmitter are inoperable and the operation indicator
light does not flash, the battery may be dead.
Replace with a new battery before the transmitter becomes unusable.
CAUTION
Make sure the battery is installed correctly. Battery leakage could occur
if it is not in ...
Mazda 6 Service Manual: Thermostat
THERMOSTAT REMOVAL/INSTALLATION
1. Remove the plug hole plate.
2. Disconnect the negative battery cable.
3. Drain the engine coolant. (See COOLING SYSTEM SERVICE WARNINGS.)
4. Remove the drive belt. (See DRIVE BELT REPLACEMENT.)
5. Remove the washer tank.
6. Remove the P/S oil pump.
Note
...