A Close Look At Engine Sludge

Engine sludge occurs when oxidized oil and contaminants build up on engine surfaces. Sludge can restrict the flow of oil to the point of engine failure and costly repairs.

As engine oil ages, oxygen reacts with the lubricants, resulting in a permanent chemical change. The oil picks up oxygen and becomes thicker, just as oxygen attacks metal surfaces and causes corrosion, it negatively affects lubricants and reduces their ability to lubricate, cool and protect components. Excessive heat speeds the oxidation process, every 18°F increase in heat, doubles the rate of oxidation.

Adding to the challenge, contaminants begin to form during normal engine operation.  Combustion gases can blow by the piston rings and contaminate engine oil. Glycol from engine coolant, water that forms with temperature fluctuations and fuel are other common contaminants that affect lubricants. Left unchecked, contaminants accelerate chemical reactions, which overload the lubricant and cause the formation of sludgegelatinous substance that wreaks havoc in engine.

Sludge can block the oil passages in the oil-pump pick-up screen, resulting in oil starvation. Often, the negative effects are cumulative rather than sudden. Many engines with variable valve timing (VVT) use oil-pressure-operated mechanical devices to change valve timing, duration and lift. Sludge can plug the solenoid screen or oil gallies and impact the operation of VVT mechanisms, eventually leading to a costly repair bill. Sludge reduces efficiency and increases time and expense on maintenance.

Signature Series versus Sludge

Signature series synthetic motor oil was subjected the sequence VG test to measure its ability to prevent sludge. As expected, signature series produce an oil pick-up tube screen virtually free from sludge. Amsoil unique combination of detergents and high quality base oils control oxidation and sludge to keep engines clean and efficient.


Amsoil synthetic lubricants not only resist oxidation sludge formation, they can help clean existing deposits in neglected engines due to superior detergency. With modern engines and equipment demanding higher-quality lubricants, it’s good to know Amsoil synthetic lubricants are formulate to protect against large in the toughest operating conditions.