What causes the antifreeze reservoir to boil over?

[KyleMarie]

The reasons for the antifreeze reservoir boiling over are: 1. The radiator stops functioning, causing the water temperature to become too high; 2. The antifreeze is not circulating, the thermostat is not opening, or the water pump is not working properly, leading to blockage in the water circulation pipeline; 3. Insufficient antifreeze or poor-quality antifreeze with a low boiling point, making it prone to boiling over. The full name of antifreeze is antifreeze coolant, meaning it is a coolant with antifreeze properties. It prevents the coolant from freezing and expanding in cold winter conditions, which could crack the radiator or damage the engine cylinder block or head. Antifreeze is a type of coolant containing special additives, mainly used in liquid-cooled engine cooling systems. It offers excellent performance in preventing freezing in winter, boiling in summer, and protecting against scale and corrosion throughout the year.

[OOmar]

I've encountered the issue of the coolant reservoir boiling over several times. It's mainly caused by engine overheating, such as when the cooling system malfunctions, the thermostat gets stuck in the closed position, or the radiator fan fails to rotate and cool down. Another cause could be insufficient coolant level, leading to poor circulation and a rapid temperature rise. There might also be air bubbles or blockages in the system, preventing the coolant from flowing properly to dissipate heat. Once boiling occurs, the dashboard temperature gauge will turn red as a warning. If not addressed promptly, prolonged high temperatures can damage the cylinder head gasket or pistons, resulting in costly and time-consuming repairs. This problem is more likely to occur during hot summer days. My advice is to wait for the car to cool down after parking, then check the coolant level and color. Top it up if it's low, and seek repairs if anything seems abnormal. Regular maintenance of the radiator and fan can prevent such issues—don't wait until you're stranded on the road to regret it.

[VanAlexis]

When I first bought my car, I had a long-distance drive where the coolant reservoir suddenly started bubbling and boiling, which really scared me. Later, I learned this was due to insufficient system pressure or overheating: a loose radiator cap causing air leaks and low pressure, a non-functioning fan leading to poor heat dissipation, or a small leak reducing the coolant level. For a DIY fix, first check the coolant level—if it's low, top it up with the same type of coolant. Then inspect if the fan is working; if not, check the fuse or relay. Ignoring this issue can lead to dangerous steam pouring from the front of the car and even a burst hose. Since learning this, I've made it a habit to check the coolant monthly to ensure it's clean and leak-free. Safe driving relies on attention to detail—don't let small issues turn into major breakdowns.

[SanJames]

Having driven for many years, I've seen this issue often—the coolant reservoir boiling over is mostly due to overheating or pressure loss. Common causes include a faulty fan not spinning, a failed thermostat, or low coolant levels due to leaks. It's crucial to pull over, let the engine cool, then check the fluid level and components; otherwise, the engine risks severe damage or even complete failure. When encountering this, I calmly pull over to the roadside, wait for it to cool, check the dashboard indicators, and promptly send it for repairs to avoid further damage. During maintenance, pay attention to cleaning the radiator to keep the system healthy.