Sludge in lubricating oils

Sludge

Sludge is a thick, semi-solid deposit that forms in lubricating oils, typically as a result of contamination, oxidation, or the mixing of incompatible oils. It often appears as a dark, sticky residue that can adhere to engine components, pipelines, or oil reservoirs.

In industrial and automotive systems, sludge formation is a common consequence of using shared funnels or containers for different oils, allowing small residues to mix. These mixed residues can react chemically or thermally with the base oil or additives, accelerating oxidation and leading to sludge accumulation.

Sludge is particularly problematic because it can:

• Block oil passages – reducing flow and impairing lubrication.
• Reduce the effectiveness of protective oil films – increasing wear on moving parts.
• Cause chemical incompatibility – leading to further oil degradation.

Preventing sludge involves proper handling of oils, avoiding cross-contamination, regular oil changes, and using additives designed to minimise deposit formation.