How to Analyze Oil Analysis

By G.C. Skipper, Contributing Editor | September 28, 2010

It has been said that oil analysis is 85 percent science and 15 percent art. The science part applies to such things as viscosity, the property in fluid that causes it to resist flow. Laboratory tests identify the viscosity index number, and that number is a common measure of changes in viscosity with temperature.

The art lies in the analysis of lab data and the interpretation of what it means.

Oil analysis is like a blood test. A blood test can tell what's wrong with you before the symptoms occur. Oil analysis can show you what's wrong with your equipment before the problem shuts it down. Yet there is one major difference. When the medical lab returns its results, the report goes to an intermediary — the doctor — who interprets the data and passes the information along to you.

Not so with oil analysis. Those reports come straight to the fleet manager, and he has to read them for himself.

It is at this point that many managers are overwhelmed by what they see — an array of codes and numbers, some of which are underlined by strange markings that look like rows of inverted "Vs."

Even laboratory professionals admit that the uninitiated often find such reports impossible to read. But understanding the fundamentals for interpreting laboratory results and recommendations will convert the task from a confusing chore to a cost-saving management tool that has a direct impact on the bottom line.

To unravel the knots of reading oil analysis reports, Construction Equipment examined the format used by Polaris Laboratories, which has four basic sections.

First is the general information that identifies the machine and, in the Polaris example, assigns a severity code based on the analysis. Polaris' codes range from 0 (normal) to 4 (most severe). If multiple elements, such as iron and chrome, are detected in an oil sample, for example, it indicates trouble. That would be classified as severity 3. However, if only iron is found, that would be a severity 2.

Second is a "comment" box that explains what's wrong with the oil and what can be done about it.

Third is an elemental analysis section that identifies, in parts per million (ppm), the amounts and type of wear particles, contamination and additives found in the oil, such as iron, lead, copper, tin, silicon and others.

Finally, the test data section lists test results according to age of the sample, oldest to most recent, top to bottom.

One of the most important things that equipment managers should remember is that when sending in oil samples, there is no such thing as too much information. Review the maintenance history of the unit from which the sample is drawn and provide the laboratory with as many specific details as possible, including whether or not the oil was recently changed or if it has been "sweetened" by adding oil.

The report will then include that information, such as engine type, unit the sample came from, and the equipment manufacturer's name, model number, and OEM standard maintenance guidelines. The report will also include the lubricant manufacturer, type and grade of the lube, filter types and their micron ratings, sump capacity, type of environment in which the equipment operates, date sampled, date received and date returned. The report should also identify the lab location where the test was completed and the lab number assigned to the sample. These can be used as a reference number if the equipment manager has questions or concerns about the report.

The comment box contains explanations and, if necessary, recommendations from a data analyst at the lab. Recommendations could be as simple as an oil change. Or, the lab might suggest specific actions be taken, such as running a check on the source of significantly high levels of silicon and aluminum (dirt) found in the sample.

The elemental analysis section of the report identifies the type and amount of wear particles, contamination and oil additives found by the lab. Determining the metal content sounds an alarm as to the type and severity of wear occurring in the unit.

Test results are listed according to age of the sample, oldest to most recent, top to bottom. Significant changes are typically flagged (Polaris uses "^" symbols, or carrots) to identify trends with a particular piece of equipment. For example, a severe change in the levels of bearing metal suggests an inspection of the gear and/or bearing assembly for excessive wear.

If a fleet manager receives multiple reports, they should analyze the documents in order of importance, starting, of course, with the highest severity reports. If the report suggests that maintenance action be taken, consider all other available diagnostic information, such as vibration, in-line sensors and so forth. Then act on the recommendation or order more testing. If a lube change is suggested due to contamination, act on the recommendations to ensure field integrity.

If resampling is recommended, immediately send a second sample to the lab to verify results. If there are no recommendations or resampling suggested, monitor the unit and take oil samples at normal intervals.

After reviewing the highest severity reports, review the cautionary reports. Pay particular attention to this data, because it becomes more useful as more data is required. Trends will become easier to identify and appropriate actions will become clearer.

Some sample results might be borderline. In that case, some wear and contamination results are flagged but they don't necessarily indicate failure mode or results are not significant enough to warrant action.

The best results, of course, are the reports that contain numerous zeros and few carrots, meaning that everything is normal. Equipment managers tend to ignore these reports and file them. But, as with severity and cautionary reports, normal reports should be reviewed as well. This enables managers to determine benchmarks for that particular equipment. When those numbers change suddenly, they will jump out.

As valuable as oil analysis is in heading off maintenance trouble, keep in mind that no test is perfect. Each one has its limitations. Never tear down an engine, for instance, based on one oil analysis. Run repeat tests, run more sophisticated tests, and track the trends before taking the unit apart.

Whether viewed as science or art, knowing how to read oil-analysis reports is essential for stopping machine failures before they occur.

[Editor's note: Information and graphics for this article were provided by Polaris Laboratories and by Ray Thibault, president, LTC (Lubricants Training and Consultants).]

Severity Status
The top section of an oil-analysis report should identify the equipment that's being tested by type, model and manufacturer. Lubricant type and grade appear beneath the equipment identification. Polaris includes a severity code, which appears on the top of its reports. Other pertinent information includes filter types and their micron rating; sump capacity; lube time, which indicates how long the oil has been used; dates sample was received, completed and returned; customer account number; the lab number assigned to the sample; and the lab and location where the test was done.
EQUIP ID 7602 FRONT DIFF
ALT ID  
CUSTOMER  
LOCATION  
UNIT TYPE DIFFERENTIAL
APPLICATION CONSTRUCTION
MFR MACK
MODEL RD688S
LUBE/FLUID MFR SHELL
LUBE TYPE SPIRAX
GRADE SAE 85W140
FILTER TYPE  
SUMP CAPACITY 5
HYD SYS PRESS  
MICRON RATING  
LUBE TIME 20000
UNIT TIME 402653
LUBE ADD 5
DATE SAMPLED 6/6/2005
DATE RECEIVED 6/13/2005
DATE COMPLETED 6/14/2005
ACCT #  
LAB # H 162303 JJP

The bottom section of the Lab report depicts the actual test results. The dates in the left-hand column are the dates samples were received, oldest to most recent, top to bottom. Numbers that are underlined with carrot symbols are flagged because they exceed pre-set warning parameters. In addition to listing the samples by date received, they are also assigned a lab number (the column next to the dates at the left side of the page.) The third column from the left indicates whether the oil was recently changed or not. Viscosity, which measures lubricant resistance and oxidation and indicates the breakdown of lubricant, is also recorded here. Oxidation prevents additives from working and therefore promotes increased acid content. Although columns 9 and 10 (from the left) are blank in the report shown here, they represent the total acid number (TAN) that tells you the amount of acid present in the lubricant and the total base number (TBN) that measures the lube's ability to neutralize acid.

The elemental analysis section, labeled Test Report, pinpoints contaminants such as iron, copper, nickel, aluminum, chrome, lead and tin. Wear metals can identify components within the equipment that are wearing. Excessive levels are flagged by carrot symbols. This section also identifies additives such as calcium, magnesium, barium and boron.

Quick Tips
  1. Review highest severity reports first.
    • If maintenance action is recommended, consider all other diagnostic information. Then decide whether to act on the recommendation or order more testing. If a lubricant change is recommended, do it immediately to ensure fluid integrity.
    • If resampling is recommended, send a second sample in immediately or at half normal sample intervals to verify results.
  2. Review cautionary reports.
    • As more data are acquired, trends will become easier to identify. Once identified, act on them.
    • Borderline results should be flagged.
  3. Review normal reports. Understand normal, or benchmark, levels for each unit. Trends are much easier to recognize.



 

 

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