Cavitation corrosion, Cavitation-accelerated corrosion, Cavitation, pitting and pinholes
Sometimes erroneously called electrolysis, which is in fact an entirely different process with similar results.
Cavitation erosion commonly occurs on the outside of diesel engine wet sleeves. This has been the subject of research by engine and component manufacturers over many years.
Wet cylinder liners have hollow spaces or cavities in the water jacket area however, these are usually only visible at the thrust and/or opposite side in the area around the top or bottom dead center of the piston.
The cavitation damage (pitting) is caused by vibrations of the cylinder liner.These vibrations can occur at the cylinder wall due to the contact alteration of the piston in the top and bottom dead center and be transmitted to the surrounding water jacket. When the cylinder wall moves back during a vibration cycle, a vacuum forms for a brief instance, resulting in vapor bubbles in the water. When the coolant column vibrates back, the vapor bubbles implode and the water flooding back onto the cylinder liner causes material erosion. It also often occurs around the liner ‘o’ ring sealing lines.
Cavitation damage is promoted by the following points:
- Insufficient anti-freeze in the coolant which could reduce the formation of vapor bubbles.
- The cooling system, e.g. the radiator cap, has a leak. This prevents pressure forming in the cooling system, promoting the formation of vapor bubbles.
- The cylinder liner in the crankcase has excessive clearance. Therefore,the vibrations caused by the contact alteration of the piston cannot be sufficiently absorbed.
- An incorrect coolant (acidic water, etc.) has been used
- The engine is operating in an insufficient temperature range. Therefore,the pressure level of the coolant is too low, promoting the formation of vapor bubbles. The piston does not reach its operating temperature, has excessive clearance and displays insufficient smoothness during contact alterations. An insufficient temperature range can be caused by the following:
- The thermostat or the thermo switch is defective.
- The viscous clutch of the fan wheel is defective, i.e. the fan wheel is driven permanently
- Always check the cooling system (radiator cap, hoses, clamps) for leaks.
- Ensure there are no air leaks in the cooling system.
- Ensure there is sufficient anti-freeze with corrosion protection. Replace Regularly
- Correctly bleed the cooling system when filling to ensure there are no trapped air pockets
- Make sure the cooling system is functioning correctly (thermostat, fan,thermo switch).
- Only use distilled water in the cooling system.
- Apply special protective coatings to the water jacket region of the sleeve outside surface E.g. chrome, copper, plasma, ceramic.