HOUSING-MOTOR 4875911 - Caterpillar

Magnified view of the bottom surface of a top piston ring that shows evidence of corrosive wear.Corrosive wear can be most easily identified by the presence of hundreds of small black pits on the bottom surface of the top piston ring. These pits can be seen with a 10X or 20X eye piece.
Corrosive Wear Prevention
The best way to prevent corrosive wear is to minimize the occurrences of an over cooled engine and limit used oil TBN to 50 percent of new oil. The number one way to have an over cooled engine is for one or more of the four jacket water thermostats to be stuck open. A thermostat will be come stuck open as a result of a cooling system that has been poorly maintained, or having only raw water (no inhibitor or antifreeze). Raw water or poorly maintained coolant will allow the cast iron cylinder block to oxidize and deposit small iron particles into the coolant. These iron particles will get into the moving parts of the thermostats and cause them to stick open.
The recommended interval for thermostats to be changed is every 6000 hours.Also, to minimize corrosive wear, the engine's oil must be changed so the oil's TBN does not drop below 50 percent of the new oil's TBN as per ASTM D2896. If the oil's TBN gets too low it will not neutralize the acids that form during combustion. If these acids are not neutralized, corrosive wear will occur.