What Causes High Coolant Temperature in Old Jetta?
2 Answers
Introduction to the causes of high coolant temperature in old Jetta is as follows: 1. Malfunctioning electric fan: Normally, the electric fan has two gears: a low-speed gear and a high-speed gear. The high-speed gear usually operates when the air conditioning pressure is too high or when the engine coolant temperature reaches 103 degrees Celsius. If your car's electric fan lacks high-speed operation or the high-speed rotation is insufficient, the above phenomenon will definitely occur. 2. Thermostat opening too small: If the thermostat's opening is too small at normal temperature, it will slow down the circulation speed of the engine's coolant, leading to high coolant temperature at low speeds. 3. Water pump slipping: The water pump impeller of the Jetta is made of plastic. If the shaft part cracks, it can cause slipping when the coolant temperature is high, resulting in high coolant temperature.
My old Jetta also had overheating issues last year, and it took several attempts to figure out the root cause. The main problem was the aging cooling system—the radiator fins were clogged with dust and willow catkins, blocking airflow no matter how hard the fan worked. Additionally, the Jetta's thermostat is prone to sticking; when I opened it, I found it full of rust debris, which prevented the coolant from circulating properly and dissipating heat. Worn water pump impellers are another hidden danger—during inspection, I noticed the blades were completely flattened, reducing coolant flow. Older cars also tend to develop leaks at hose connections, causing slow coolant loss that often goes unnoticed, so regular checks are crucial. Finally, a word of advice: if the temperature gauge hits red, never push your luck—shut off the engine and call for help immediately, or you risk blowing the head gasket and facing costly repairs.
