What Causes Pitting in Cylinder Liners?

Pitting in cylinder liners is a direct result of cavitation erosion. This type of erosion develops from normal mechanical and chemical processes that take place during engine operation.

Cavitation of the cylinder wall begins when air bubbles remove the wall’s oxide film, which protects the metal from coming into contact with oxygen and corroding. Flexing of the cylinder wall (after fuel combustion) causes the cylinder liner to vibrate, and creates vapor bubbles in the coolant. These vapor bubbles form on the outside of the cylinder wall and explode inward, or implode, resulting in tiny pits on the cylinder wall’s protective oxide layer. When vapor bubbles continue to implode, enough energy is released to physically attack the cylinder wall and remove the oxide film. Corrosion and pitting then take place at a high rate.

If a pit breaks through the cylinder wall, coolant can leak into the cylinder and contaminate the lube oil. A sludge forms that can interfere in ring and bearing functions. Wear rates increase significantly and engine seizure may result.

The best way to prevent cavitation from occurring is to follow your engine manufacturer’s recommendations on additive replacement. When using a standard heavy-duty coolant, SCA (Supplemental Coolant Additive) should be added every 250 hours to help replenish the eroding oxide film. Caterpillar has recently introduced an Extended Life Coolant (ELC), which provides a substantial amount of protection and lasts longer than standard heavy duty coolants. ELC eliminates the need for multiple additive replacements – requiring only one addition of extender at 3,000 hours.

If you modify your cooling system, remember to keep the pressure cap furnished with the expansion tank. Removing this cap allows a lower operating pressure inside the engine. That will cause more vapor bubbles to form, resulting in cavitation.


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