What are the three main reasons for coolant overflow from the reservoir?
2 Answers
The three main reasons for coolant overflow from the reservoir are: 1. The reservoir cap is damaged, causing high temperature inside the reservoir; 2. The coolant level exceeds the upper mark on the reservoir; 3. A faulty thermostat leads to excessively high water temperature, preventing the coolant from entering the engine water passages for major circulation. The full name of coolant should be antifreeze coolant, meaning it has antifreeze properties. Coolant prevents freezing and expansion damage to the radiator and engine cylinder block during cold winter parking. Coolant is a specially formulated additive-containing liquid primarily used in liquid-cooled engine cooling systems, featuring excellent properties such as winter antifreeze protection, summer boil-over prevention, and year-round anti-scaling and anti-corrosion performance.
Last time, the antifreeze in my car kept bubbling out of the reservoir, especially during traffic jams or on highways. If this stuff overflows, it could damage the wiring. There are three main reasons for this. First, thermal expansion is too intense—when the engine gets hot, the coolant expands significantly, and if the reservoir is too small or has cracks, it spills everywhere immediately. Second, there's an issue with the pressure system—the radiator cap might be old and no longer sealing properly, or there could be air trapped in the cooling system. More bubbles mean increased pressure, forcing the liquid out. Third, the antifreeze itself might be the problem—either overfilled above the max line during topping up or an incorrect mixing ratio causing abnormal expansion due to density issues. It's recommended to check the fluid level before every trip, avoid filling past the max line, and replace the coolant regularly to avoid trouble.
