Using oil analysis results to determine required maintenance action must take careful thought. Before any action is taken, the current operating conditions and performance of the equipment must be evaluated by the maintenance manager. Other considerations are:

  Equipment availability

  Equipment age

  Warranty claim responsibilities

  Cost of repair vs. Equipment replacement

  How critical is the job application

  Do you have other equipment to replace the unit while out of service

  Man hours may be lost while equipment is out of service

  Previous maintenance records

  Equipment need vs. downtime

  Operator logs

 Once the decision is made to inspect or repair equipment, the used oil analysis reports can help pinpoint areas for maintenance action. Review test results for problem areas. Typical problems are:

Viscosity of Lubricants

If the viscosity has increased or decreased by more than one grade, the reason for the change should be investigated. Consult the oil analysis training manual, available from the lab, for cause of problems.

Fuel Soot

Fuel soot levels will vary depending on engine types and equipment applications. Typical fuel soot levels requiring maintenance action will be around 2% by weight. Consult training manual. Fuel soot, alone, without any other problems may not require any action. Consult manual for solutions.


Fuel levels may vary depending on equipment. 4% fuel usually requires inspection or repair. This level of fuel may affect the viscosity and cause abnormal wear. Consult manual for solutions.


Water greater than .05 requires maintenance action and/or oil change. Consult manual for sources.

TBN (Total Base Number)

If oil shows a TBN of less than 1/2 the original TBN of new oil it should be changed.

TAN (Total Acid Number)

Typically, new engine oils have low TAN's of less than 2. If the used oil shows an increase of double the values of the new oil, it indicates a need to change the oil.

Elemental analysis will have different levels of allowable parts per million (ppm) for different types of equipment/engines. Some basic guidelines are as follows:

Silicon (Si) Dirt

20 parts per million is normally considered high, however, 20 ppm without any related wear may indicate a contaminated sample or silicon from a source other than dirt.

Typically wear metal limits to use as guidelines can be classified as moderate or critical. Moderate levels usually require no maintenance action. Basic Guidelines are:

Fe (Iron) 100ppm 150ppm
Cr (Chromium) 10ppm 30ppm
Al (Aluminum) 10ppm 30ppm
Cu (Copper) 30ppm 60ppm
Pb (Lead) 30ppm 60ppm
Sn (Tin) 15ppm 30ppm
Ni (Nickel) 5ppm 10ppm

Increases in wear metals without an apparent reason or cause should be evaluated carefully. If all factors are normal, the wear rates should be fairly consistent unless a problem is developing.

Changes in viscosity, soot levels, fuel dilution, water, TBN's, TAN's, dirt (Si) and glycol contamination may affect the wear metals and may require maintenance action or inspection. If there is an effect - there must be a reason or cause. New engines or engines recently overhauled will have high levels of break in wear.


Wear metals will increase slowly over a period of time and moderate increases may be considered normal, Sudden increases without a reason or cause indicate a potential problem. An increase of over 50% of the baseline trend should be investigated to determine the cause.

The other wear metals - Mo, Ag, Ti, V, Sb - are not typically in the majority of diesel engines, especially construction and over the road equipment.

Na ( Sodium), B (Boron), and K (Potassium) are found in some engine oils as additives, however, they are typically indicators of coolant (Antifreeze) in oil. Levels of these elements found in quantities of 30 to 50 parts per million greater than levels in new oils are cause for concern. Samples with high levels will be tested chemically for coolant/antifreeze. Antifreeze at any level requires inspection and maintenance action.

Mg (Magnesium), Ca (Calcium), Ba (Barium), P (Phosphorus), and Zn (Zinc) are additives used to develop specific properties for different lubricants. These will vary depending on the manufacturer and oil type. The laboratory reviews these to ensure the proper oil is in use. Changes in these levels will vary and will be commented on only if the lab has a question, or a problem has been detected that may relate to additives.


Oil Analysis Report Interpretation Variables

Points to consider when evaluating oil analysis results.

Oil analysis results may vary from sample to sample and for the most part this is expected. Some factors that may affect the results that should be thought about when reviewing reports are:

 Inconsistent Sampling

The time and activities involved in sampling need to be consistent from sample to sample. Questions to ask yourself are:

Remember, many things affect lab results and the effect may of may not be normal depending on variables discussed at the beginning of the paper. Always consult equipment records, manufacturer, lube suppliers, and the laboratory if you have any questions.