Why does the car's water temperature rise when idling with the AC on but remains normal while driving?
3 Answers
Because the ambient temperature is relatively high, coupled with the heat generated by the engine and other machinery, the water temperature rises when idling with the AC on but returns to normal while driving. Below are solutions for high water temperature when idling with the AC on: 1. Cleaning: Visit a professional repair shop or 4S store to clean the condenser, radiator, and inspect the fan and cooling system. 2. Rinsing: When washing the car, you can appropriately rinse with a hose, targeting the gaps around the car emblem where the condenser is located. Over time, it can accumulate dust, leaves, and other debris. 3. AC: Turn on the internal circulation when using the AC to save costs, maintain a lower temperature inside the car, and avoid waste. 4. Cooling: Use intermittent cooling by turning off the AC once the car's interior temperature drops and turning it back on after some time.
I've been driving for many years and encountered this situation multiple times. At idle, such as when parked with the AC on, the engine runs at low RPM, and the fan and water pump rotate slowly, resulting in inherently low cooling efficiency. When the AC compressor kicks in, it adds extra load to the engine, making it even hotter. However, since the car isn't moving, there's no airflow to help cool the radiator, so the water temperature tends to spike. Once you start driving, the engine RPM increases, the fan and water pump work more vigorously, and the airflow from the car's speed helps cool the radiator, naturally stabilizing the temperature. Checking isn't complicated: pop the hood, idle the engine with the AC on, and see if the fan is spinning. If the temperature gauge stays high, the radiator might be clogged or blocked by leaves and needs cleaning. Prolonged overheating can damage engine gaskets, so fixing it early gives peace of mind.
From a technical perspective, this phenomenon is quite common. At idle, the engine speed is usually only a few hundred RPM, which limits the capacity to drive the water pump and cooling fan. When the air conditioning compressor engages, the engine needs additional power to compress the refrigerant, increasing heat output while heat dissipation struggles to keep up. During driving, the engine speed rises to one or two thousand RPM, improving the efficiency of the coolant circulation by the water pump, and with the assistance of airflow, the temperature difference decreases. The core issue may lie in the cooling system, such as a stuck thermostat or insufficient fan speed. During routine maintenance, regularly replacing the coolant and checking for debris on the radiator fins can effectively prevent problems. If the water temperature frequently rises abnormally, it's essential to inspect the coolant temperature sensor or control module to avoid escalating into a major issue.
