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SAE Technical Papers Contamination
Lube oil contamination accounts for 70 to 80% of all failures and wear problems. The wear process promoted by oil contamination leads to diminished fuel efficiency, shorter useful oil service life, increased engine down time, reduced component life, loss of engine performance, and an overall increase in operating costs.
Contaminant particles responsible for this damage are in the size range of the dynamic lubricant films separating moving engine component surfaces: 10 microns and smaller. Typically these particles pass through the oil filter and continue to build up in the oil system. By making simultaneous contact with opposing surfaces these harmful particles focus the load onto a small area, degrading the surface and perpetuating a chain-reaction-of-wear.
There are 3 categories of oil contaminates active in the engine wear process:
1. Solid particles, including wear debris and soot, which damage mechanical components and catalyze lubricant breakdown;
2. Liquid contaminates, including fuel and water, which corrode metals and hinder the functioning of lubricants; and
3. Gaseous contaminants, including acidic combustion products, which corrode component surfaces and degrade the oil.
The predominant harmful impurities in engine oil are metallic particles and metal oxides. Typically there are well over 10,000 contaminant particles per milliliter of lube oil. Furthermore, approximately 90% of these particles are less than 10-microns in size. It’s important to note that these particles generate about 3.5-times more wear than particles greater than 10-microns in size. This wear occurs because these particles are the size of, or slightly larger than the dynamic oil films separating opposing surfaces.
Numerous studies have established a number of important points regarding the relationship between lube oil contamination and engine wear. In the following SAE Paper 881827 substituting a standard 20-30 micron filter with a 10-micron filter resulted in:
 A reduced concentration of contaminant particles by a factor of 10-15 times;
 A reduction in the four major wear metals monitored;
 The filter was capable of operating more than twice the recommended
service life; and
 Permitted the lube oil service life to be more than doubled without
adverse engine wear or lubricant degradation.
In summary, controlling particle contamination in the 0-10 micron size range retards the chain-reaction-of-wear, resulting in significant reductions in component wear and lubricant breakdown. The beneficial consequences include greater component life and reliability, increased oil change intervals, increased fuel efficiency, and a reduction in overall maintenance costs.
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Impurities
SAE 881827
Summary
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