SLUDGE FORMATION

Abstract

The formation of sludgy deposits in gasoline engines first became a major problem during the early 1960s, prompting a considerable amount of investigative work and resulting in changes both to engine design and lubricant formulation. Some 20 years later during 1984 and 1985, the accumulation of semi‐solid materials in the gasoline engine again became an operational problem in Europe, the deposits being described as “hot sludge” or “black sludge”. The most serious occurrences were first noted in Germany. The deposits varied in consistency from a soft oily paste to a hard black brittle layer. These were usually found on the cooler inner surfaces of the crankcase and in particular, tended to accumulate initially in the engine top cover or on the top of the cylinder head (valve deck). Engine malfunctions and in extreme cases, total engine failure sometimes resulted from accumulation of these deposits, the most serious engine damage usually arising from blockage of the oil pump pick‐up screen and the attendant loss of oil supply. A number of European engine manufacturers were experiencing this type of failure within warranty periods, and the elimination of the problem became of major importance. Formation of sludge in gasoline engines has since been seen in countries outside Europe, notably the USA and Japan.