What Causes Bubbles in the Engine Radiator?

[VanessaLee]

During vehicle operation, water bubbling up from the radiator cap is primarily caused by poor combustion chamber sealing, which allows high-temperature combustion gases from the diesel engine to enter the cooling water cavity. Therefore, to address the issue of water bubbling in the radiator, the combustion chamber sealing problem must first be resolved. The main causes of combustion chamber sealing failure are as follows: 1. Cause one: The cylinder head is warped or deformed, resulting in an uneven bottom surface. 2. Cause two: The top surface of the cylinder block is uneven. 3. Cause three: Insufficient torque on the cylinder head fastening bolts, or the bolts not being tightened evenly in several steps using a symmetrical cross pattern. 4. Cause four: Residual debris in the bolt holes at the top surface of the cylinder block reduces the torque on the cylinder head bolts, leading to a "false tightness" phenomenon. 5. Cause five: The threaded holes for the cylinder head bolts on the cylinder block are not properly tapped or threaded to the required depth.

[DiLeila]

In the previous car repair case where bubbles were observed in the radiator, the direct cause was engine internal pressure entering the cooling system. In most cases, this happens due to aging cylinder head gaskets, where high-temperature and high-pressure combustion gases squeeze into the coolant through gaps, forming bubbles. If not addressed promptly, the coolant may spray and scald people, and the water temperature could soar, leading to cylinder scoring. First, open the engine hood and check the radiator surface for oil stains or coolant that appears cloudy with a gasoline smell when the engine is cold—these are telltale signs. The safest action is to immediately turn off the engine and call for a tow truck to prevent further damage. Long-term neglect of antifreeze replacement can also reduce sealing performance, so it's recommended to change it every two years. As a driver, if you notice bubbling, don’t hesitate—take the car to a reputable repair shop to check the cylinder head flatness and gasket condition. Addressing minor issues early can save significant repair costs later.

[LeAlan]

Last year while driving on the highway, my car suddenly had bubbles coming out of the radiator, which scared me so much that I immediately pulled over. After inspection at the repair shop, they said it was due to a slight deformation of the cylinder head causing poor sealing, allowing exhaust gases to seep into the cooling pipes and mix with the liquid, creating bubbles. The mechanic explained that high temperatures and aggressive driving can easily trigger this issue, especially in older engines where metal fatigue makes them more prone to problems. Besides a faulty cylinder head gasket, it could also be caused by a blocked radiator cap exhaust valve or too much dirt on the cooling fins hindering heat dissipation. Everyone should pay attention to the coolant level and color changes in daily use, and regularly clean dust and debris from the outside of the radiator. After that incident, I developed the habit of checking the temperature gauge before setting off.

[DelAllison]

Bubbling in the radiator is essentially a symptom of abnormal pressure in the cooling system, with the root cause often being combustion chamber blow-by. Cracks in the cylinder head or engine block can allow high-pressure gases to enter the coolant passages, forming bubbles that rise in the antifreeze when heated. Sometimes, prolonged heavy-duty operation of the vehicle can cause the cylinder head gasket to fail, or the radiator cap's pressure relief valve may stick, leading to excessive pressure in the cooling system. It's worth noting that if this is accompanied by emulsified engine oil or engine overheating and shaking, extra caution is advised.