Used Oil Analysis Cuts Through Myths and Mystery


There is an old adage that says, “You can’t change what you can measure.” Accurate measurements are basically facts, and you can use these facts to make measurable changes.

When it comes to engine wear protection, everyone has opinions about motor oils. But, you CAN make decisions based on facts instead of speculation. Used Oil Analysis provides those facts.

No matter your application — a turbo diesel pulling truck, a naturally aspirated drag race engine, a farm tractor, a boat, a motorcycle, a hot rod or anything in between — every situation is different and presents its own challenges. However, a Used Oil Analysis can give you the data to help navigate these challenges.

Doing Used Oil Analysis may sound complicated, but it’s ridiculously easy, not very expensive and provides a wealth of information. Collecting used oil samples for analysis is quick, and most heavy equipment dealers, like Caterpillar or John Deere, sell used oil analysis kits — usually for less than $30.

All you have to do is take a small, 3-ounce sample of lubricant directly from the engine within a couple of minutes of shutting off the engine. It is important that the engine has been properly warmed up prior to shutting it down; this step ensures the oil has been circulated well and that the sample is representative.

Next, fill out the form to identify the sample for processing and send it off to the lab. Don’t worry; 3 ounces is not considered hazardous, so you can send it via regular mail.

That’s it. You’re done. In a few days, you’ll get the results back, and you won’t need to have a Ph.D. to read the report. The lab will provide a general interpretation of results. With some additional help from the tips coming up in this article, you can interpret the results yourself.

It’s just THAT simple — and it can make a big difference.

To really stay on top of things, it is good practice to have the oil analyzed on a periodic basis, like every six months to a year for road cars and a least every few races for a race car.

With that out of the way, let’s get into the basics of interpreting oil analysis results. While correctly interpreting oil analysis results is critical for making good decisions about preventive maintenance, it is a skill that is easily learned with a little bit of experience and some training. It is important to understand the report does not always pinpoint a specific problem, but it will provide details for troubleshooting.

The results are usually organized in a spreadsheet with numbers indicating the test results. Check the report to make sure it includes your name, sample date, mileage or time on the oil, the type of oil used and the ID of the engine. The laboratory has a rating system that notifies you of normal, marginal and critical levels, so the report will list the condition of your engine and lubricant. Also, the report may include comments from the analyst who reviewed your results. These comments can help you gauge the severity of a problem and provide a suggested course of action.

Viscosity Results

Viscosity is the most important test run on the oil because viscosity is a lubricant’s most important property. The viscosity test measures a lubricant’s resistance to flow at a specific temperature. If the oil’s viscosity change is greater than plus or minus 10 percent of the new oil value, it is considered marginal. Viscosity changes greater than plus or minus 20 percent are considered critical.

If the oil does not have the right viscosity, it cannot perform properly. If the viscosity is not correct for the load, the oil film cannot be established. Without enough oil flow, heat and contamination are not carried away at the appropriate rates, and the oil can not protect the engine properly. An improper viscosity oil can lead to overheating, accelerated wear and, ultimately, failure of the engine.

Measuring Wear Metals

Interpreting an oil analysis report involves understanding the concentration of expected and unexpected elements in your oil. You can know what to expect by analyzing the new oil before putting it in the engine. This becomes your reference sample. From this, you know what metals, like Zinc and Phosphorus, are naturally in the oil, and it let’s you see which metals, like Iron, are wear metals in the used oil.

Some contaminants are picked up as the oil circulates through the engine. Other contaminants can enter the engine during routine service, or from poor filters and breathers. No matter how these contaminants get in, they can cause significant damage. Elemental analysis determines the concentration of wear metals, contaminant metals and additive metals in the oil sample. An increase in wear metals can be indicative of abnormal wear.

Just remember, Elemental analysis cannot measure particles larger than 10 microns, which leaves a blind spot to larger particles. It is also worth noting that some variance is normal in the results. Any change less than 20 ppm is typically nothing to worry about. When you see changes greater than 50 ppm, be cautious. When you see changes greater than 100 ppm, be alarmed.

Understanding Wear Metals

When looking at the wear metal levels in your test results, look at the history of each engine. This is why periodic samples are the most helpful. For example, two identical pieces of engines may have vastly different elemental results due to variations in operating conditions and maintenance practices. However, both machines could still be healthy based on the trending of the analysis results. In fact, trending is an extremely important tool in determining an engine’s health.

A good rule of thumb is to use your judgment and review the trend data. Has anything changed with the operating conditions? Have you been running the engine longer? Have you been putting more load on the engine? You can also discuss the test results with the lab analyst before making any decisions.

Watch Out For Contaminants

Contamination is a leading cause of many oil system failures. It often comes from materials such as water, metals, dust, sand and rubber. Even the smallest particles can produce significant damage, so monitoring the level of contaminants is critical – especially in a dirty operating environment.

The goal here is to detect the presence of contaminants, identify their source and determine how to prevent further entry. Contaminants can act as a catalyst for component wear. If the cycle is not broken, wear accelerates and the life expectancy of the engine is reduced. The elements that typically suggest contamination include silicon, boron, potassium, and sodium.


Water is a terrible lubricant and promotes rust and corrosion of metal surfaces, so it poses a serious threat to an engine. Dissolved water in motor oil produces oxidation and reduces the oil’s load-carrying ability. Water contamination can also deplete the oils additive package. Increased amounts of water in oil results in accelerated wear, increased friction and high operating temperatures. If left unchecked, water can lead to premature engine failure.

The Karl Fischer water test is the most common method used to analyze water levels in oil. When reviewing these test results, remember that low levels of water are typically the result of condensation, while higher levels can indicate a source of water contamination. In most systems, water should not exceed 500 ppm. Common sources of water include external contamination, internal leaks and condensation.

These are the basic facts related to Used Oil Analysis, and how to interpret the results. Implementing an analysis program may seem like a daunting task, but is actually very simple and easy to do. The results you get pay for themselves and provide the facts you need to make good decisions.