What are the causes of engine sludge formation?

[StBriella]

Engine sludge formation causes: During the continuous reciprocating operation of the engine piston, gas from the combustion chamber enters the crankcase through the gap between the piston rings and cylinder wall, which is the main cause of sludge formation. This blow-by gas contains various unburned products, dust, metal oxides, etc. After mixing with engine oil in the crankcase, it undergoes further oxidative condensation to form acidic insoluble substances in the lubricating oil. These then combine with other solids and water vapor, eventually forming sludge that settles in various locations. The sludge produced in different parts of the engine can be divided into low-temperature sludge and high-temperature sludge. Low-temperature sludge is formed by the combined action of blow-by gas (containing unburned fuel and water) and engine oil. High-temperature sludge occurs when the engine operates at high temperatures, polymerizing into larger molecules that thicken the engine oil, changing its viscosity, and over time forming sludge.