Signs of cylinder head gasket damage and causes of air leakage

Black stains are obvious signs
Excessive purging of combustion gas at the metal ring of the combustion chamber of the cylinder head gasket is one of the most common reasons, and the cylinder head must be removed.
A noticeable black stain on the metal ring or in the soft material area of the adjacent gasket is a clear sign. Due to the high gas temperature, the soft materials at these locations overheat and even burn. Gas can usually enter the cooling circuit. Rising air bubbles in the radiator or overheating of the cooling circuit (the pressure in the cooling circuit rises and the coolant overflows from the pressure relief valve, causing coolant loss) can illustrate this point. In the worst case, the metal ring is completely destroyed. However, the uniform stain of the metal ring of the combustion chamber can be regarded as normal, depending on the steel material and the surface coating used.

The most common cause

Example

Direct full-load operation after a cold start causes extreme sliding between the crankcase (grey cast iron) and the cylinder head (aluminum), and the gasket bears excessive stress. In addition, the preloading force of the cylinder head bolts under these conditions is small, which increases the clearance gap between the crankcase and the cylinder head.
The most frequent occurrence, especially in truck engines, is that the liner is not protruded to the specified level due to lack of professional knowledge, or due to installation errors, improper repair of the liner support surface in the cylinder block or the liner is not properly pressed into place. Resulting in incorrect adjustment. This causes the gasket to drop and the required sealing pressure is lost. At this time, the combustion gas can enter the rear area of the gasket, and then damage the rubber sealing element or soft material of the water injection port or the oil injection port.

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