Why does the car's water temperature rise when going uphill and drop when going downhill?

[LeDaniella]

Water temperature gauge displays the temperature after cooling by the cooling system. When going uphill, especially at a slow pace, the cooling system's efficiency is significantly lower compared to when the vehicle is moving on level ground, leading to a natural rise in water temperature. During downhill driving, the engine load is smaller, generating relatively less heat, so the drop in water temperature is normal. Additional information: 1. Principle of the water temperature sensor: The electronic control unit measures the engine's coolant temperature based on this change—the lower the temperature, the greater the resistance; conversely, the smaller the resistance. The electronic control unit uses this change to measure the engine's coolant temperature as a correction signal for fuel injection and ignition timing. 2. Structure of the water temperature sensor: The car's water temperature sensor is installed on the engine block or cylinder head water jacket, in direct contact with the coolant, and is used to measure the engine's coolant temperature.