What are the causes of coolant boiling?

[AlinaRose]

The causes of coolant boiling: 1. High-temperature weather leading to coolant boiling; 2. Overloaded operation of the air conditioning system; 3. Failure of cooling components causing coolant boiling. Coolant boiling usually refers to the situation where the working temperature of a car engine exceeds the normal operating temperature range, affecting the machine's normal operation and potentially damaging it. The boiling temperature of coolant is generally above 85 degrees Celsius, with different models having different standards. The higher the temperature exceeds the normal range, the greater the damage to the machine. Regularly check if the cooling fan is working properly, if there are any coolant leaks in the radiator, and if the coolant level is sufficient. If the radiator is leaking, it should be repaired or replaced promptly. If the coolant level is low, it should be replenished in time. If the coolant appears cloudy or deteriorated, it should be replaced.

[MacHenry]

I've experienced the radiator boiling over a few times, which essentially means the engine heat can't dissipate properly. The most common causes are insufficient or degraded coolant - too little fluid or aged coolant both reduce cooling capacity. Radiators clogged with willow catkins or dust are also frequent culprits; that's what caused my last boil-over. Fan failure is another major reason - whether it's an electric fan or viscous fan, if it stops spinning, temperatures will skyrocket. A faulty water pump disrupts coolant circulation, and a thermostat stuck in small circulation mode makes matters worse. Other potential causes include engine overload (like heavy-load hill climbing) or cylinder head gasket failure allowing combustion gases into the cooling system. Regular maintenance is key: check coolant level and concentration periodically, clean radiator surface debris, and verify fan operation before long trips.

[LaStephen]

The boiling of the radiator is mainly due to issues in the cooling system. When the engine is running, the temperature rises sharply. If the coolant is insufficient, deteriorated, or has an incorrect concentration, its heat transfer capability is significantly reduced. Radiator blockage is particularly easy to overlook—spring willow catkins and lint clogging the cooling fins, or internal rust and scale buildup in the radiator, can all hinder heat dissipation. If the fan fails, it's even worse—my neighbor's car once broke down due to overheating because of this. A faulty water pump can stop the coolant from circulating, and a stuck thermostat can block the main cooling circuit. Long-term high-load driving, such as towing a caravan up a steep slope, leads to faster heat accumulation. Another issue could be a blown head gasket, allowing exhaust gases to directly enter the cooling pipes. When dealing with this, never open the radiator cap immediately—wait for it to cool down before adding coolant.

[Silva]

Boiling over in the radiator essentially means the cooling system has failed. From my experience in auto repair, these are the typical scenarios: Coolant shortage or degradation is the most common cause, followed by radiator scale blockage. Fan failure has the highest occurrence rate, whether due to motor issues or sensor problems. A broken water pump belt or corroded impeller halts coolant circulation, and a stuck thermostat is equally dangerous. Prolonged high-RPM engine operation, especially when towing heavy loads, makes overheating highly likely. The most troublesome case is a blown head gasket, where hot combustion gases directly enter the cooling passages. If boiling occurs, immediately pull over, turn the heater to maximum to assist cooling, then check for leaks in the system. For prevention, regular coolant replacement is crucial, and an annual radiator fin cleaning is equally essential.