Under low temperature engine operation, sludge appears as insolubles in the lubricating oil or as deposits on engine parts. Its formation is initiated by liquid oxidation products, inorganic salts, and polymerized organic compounds that pass the piston ring zone. The liquid oxidation products undergo further chemical reaction in the crankcase oil medium, forming solid “sludge binders.” These “binders” are the essential ingredients that the oil must contain before the organic solids (carbonyls, sulfur, and nitrogen derivatives and polymerized hydrocarbons), inorganic salts, wear particles, and soot can be deposited as sludge.
