Mazda 3 Service Manual: Thermostat Removal/Installation [Mzr 2.0, Mzr 2.5]
Never remove the cooling system cap or loosen the radiator drain plug while the engine is running, or when the engine and radiator are hot. Scalding engine coolant and steam may shoot out and cause serious injury. It may also damage the engine and cooling system.
Turn off the engine and wait until it is cool. Even then, be very careful when removing the cap. Wrap a thick cloth around it and slowly turn it counterclockwise 2.5 turns. Step back while the pressure escapes.
When you are sure all the pressure is gone, turn the cap using the cloth, and remove it.
1. Remove the battery cover..
2. Disconnect the negative battery cable..
3. Remove the plug hole plate..
4. Remove the aerodynamic under cover No.2 and splash shield as a single unit..
5. Drain the engine coolant..
6. Remove the generator drive belt with the A/C drive belt still installed and set it out of the way. (MZR 2.0).
7. Remove the drive belt. (MZR 2.5).
8. Remove the drive belt auto tensioner. (MZR 2.0).
9. Remove the idler pulley. (MZR 2.5).
10. Remove in the order indicated in the table.
11. Install in the reverse order of removal.
12. Refill the engine coolant..