What is the reason for the radiator overflowing when the cylinder gasket is not damaged?

[Ramon]

The reasons for the radiator overflowing when the cylinder gasket is not damaged are as follows: 1. The return pipe from the upper water chamber of the radiator or the upper part of the thermostat to the expansion tank is blocked or not smooth, the cooling system is blocked, the antifreeze circulation is affected, causing the cooling liquid to overflow from the radiator filler port. 2. In addition, not replacing the antifreeze for a long time or using tap water instead of antifreeze can easily cause damage to the radiator cap. This situation can also lead to the radiator spitting water, and only replacing the radiator cap is needed. If antifreeze sprays out of the radiator regardless of the water temperature, this situation may be due to a problem with the cylinder gasket. If the cylinder gasket is damaged, or if the cylinder liner or cylinder head has cracks or sand holes, because the pressure of the compressed air or combustion gas in the cylinder is greater than the pressure of the cooling liquid in the cooling channel, the gas enters the engine water channel through cracks or sand holes, increasing the pressure in the water channel, which will cause the cooling liquid to overflow from the radiator filler port.

[DelFelix]

I've encountered a similar situation before. At that time, the cylinder head gasket was checked and found to be fine, but the radiator kept bubbling and overflowing, which really gave me a hard time. Later, I learned that this is usually caused by issues in the cooling system, such as a water pump failure. If the water pump isn't working, the coolant can't circulate properly in the engine, leading to heat buildup and boiling. The water pump acts like a heart, pushing coolant through the system. If it fails, the coolant flow is obstructed, causing the radiator temperature to spike and overflow. Another possibility is a stuck thermostat. It's supposed to open during a cold start to allow coolant flow, but if it's stuck, it blocks the path, causing the engine to overheat. Additionally, checking if there's enough coolant or if the pipes are clogged is also important, as debris buildup can obstruct the flow. If the cooling fan isn't working, it can also cause the radiator to overheat, especially noticeable at low speeds or when idling. I think if you notice this kind of problem, don't push through—pull over immediately to check if the fan is running or head to a repair shop to inspect the water pump and thermostat to prevent engine overheating and major repairs. Always keep an eye on the coolant level—don't overlook these details.

[JustinRose]

I've been driving for quite a few years, and the issue of coolant overflow sounds quite alarming, especially when the cylinder head gasket was just inspected and found to be fine, yet it still overflows. From what I've gathered from fellow car enthusiasts' shared experiences, this is mostly caused by problems in the cooling circulation system. The water pump plays a crucial role—it drives the coolant flow. If it malfunctions, the coolant can't circulate far before overheating, causing the radiator to overflow. The thermostat is another common culprit; if it gets stuck in a partially open position, it's like closing a valve and letting the coolant boil inside the engine. Also, keep an eye on the fan—if it fails to spin, the hot air can't dissipate, and the temperature rises, leading to boiling coolant. I suggest you start with some simple checks: pop the hood, check if the coolant level in the radiator is sufficient, see if the fan kicks in when the engine gets hot, and feel the hoses to see if they're warm. If all these seem normal, it might be due to aging pipes causing blockages or incorrect antifreeze concentration making the coolant prone to boiling. Addressing this promptly is crucial—don't wait until the radiator bursts, as repairs will cost much more then. It's safer to have a professional mechanic run diagnostic tests with proper tools—let's not take unnecessary risks.

[DelJade]

From my perspective, if the coolant is boiling over but the cylinder head gasket is intact, it's often due to issues with the water pump or thermostat. The water pump is responsible for circulating the coolant; if it fails, the coolant stops flowing, causing the engine to overheat and the coolant to boil. The thermostat regulates coolant temperature—if it gets stuck closed, the coolant becomes trapped, leading to a rapid temperature rise. Fan malfunctions are also common; they're supposed to provide airflow for cooling, but when broken, they become useless. I recommend checking these components, especially the thermostat and water pump, to prevent long-term engine damage. Additionally, inspect the cooling system for air pockets, which can cause localized overheating—a simple bleeding procedure might help.