Engine Performance as Influenced by Lubricant Deterioration

Tests employed for the evaluation of used lubricating oils generally involve the determination of changes in viscosity, insolubles buildup, contamination with metals, fuel, water, glycol and other physical and chemical changes.

The author attempts to point out the relative significance of these various tests in terms of engine operation. Engine test data is also presented which shows the relationship between the oil condition measured by some of these tests and the engine performance characteristics.

The data indicates that increase in alkalinity improves rust protection and reduces engine varnish and PCV valve restriction in certain additive combinations. Engine wear appears to be associated with the accumulation of contaminants in the lubricant measured as pentane insolubles and total acid number.