According to what you said, since you removed the thermostat and replaced the fan coupler, since you have never seen the existing car, let me help you analyze the main reasons for the high water temperature. Firstly, check whether the cooling system of the engine is too dirty, resulting in poor antifreeze circulation and poor heat dissipation when the vehicle is driving at low speed; Also, if the engine has too much carbon deposit or the air conditioning system pressure is too high, it may also lead to too high water temperature when the air conditioner is turned on. You can check from these aspects.
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