Why is the coolant temperature too high?
3 Answers
Coolant temperature too high reasons are: 1. The outer surface of the radiator is too dirty or internally clogged; 2. Insufficient coolant or leakage; 3. Thermostat damage; 4. Water pump damage; 5. Cooling fan and control system damage. The solution for high coolant temperature is: Loosen the radiator cap slightly, wait for the steam to slowly escape, and after the radiator pressure drops, add cold water or coolant. The main functions of coolant are: 1. In winter when the vehicle is parked, it prevents the coolant from freezing and expanding, which could crack the radiator and freeze the engine cylinder block or head; 2. In summer when temperatures are high, it effectively prevents boiling, avoiding the phenomenon of overheating.
I've repaired many cases of high engine temperature, and the most common issue is insufficient coolant. It could be due to leaks or evaporation, with aging pipe connections being the most easily overlooked source of seepage. Secondly, the radiator might be clogged with bugs and willow catkins on the outside, and when the fan speed can't keep up, the cooling efficiency plummets. The most troublesome situation is when the thermostat gets stuck in the closed position of the large circulation loop, causing the coolant to only circulate within the engine's small loop, leading to a direct temperature spike. Corrosion or breakage of the water pump impeller can also halt coolant flow. During summer when the air conditioning is on or during prolonged uphill driving, the engine is under greater load, making it more prone to triggering high-temperature warnings. When the dashboard's temperature gauge needle crosses the midpoint, it's time to pay attention and immediately stop to check the coolant level in the auxiliary tank. The repair cost for a blown head gasket could buy half a car, so never push your luck.
From my experience, cooling system issues are like a chain reaction. Insufficient coolant leads to poor circulation, but why is there a shortage? It could be due to cracks in the radiator or bulging hoses. Scale buildup inside the radiator is like clogged blood vessels, especially noticeable in cars that have used tap water. A burnt-out electronic fan relay or a faulty thermostat switch can prevent the fan from turning on at the intended 80 degrees. Water pump shaft seal leaks are the hardest to detect—they drip slowly over time, and by the time you notice, the engine is already overheating. Modified cars with improperly connected high-power electrical devices are also at risk, as an overloaded alternator can cause the entire system to overheat. Remember to regularly check the temperature difference between the upper and lower hoses by hand—if both are scalding hot, it means the thermostat isn’t opening, and immediate action is required.
