Bottom Line
Using oil analysis as a predictive tool to get longer life out of your engine

By Jerry Sims
President of Gulf Coast Filters Inc.r


An oil analysis report allows you to monitor the amount of contamination, the wear rates, and the physical characteristics of a lubricant. Oil analysis is a tool that can allow you to have control over the reactions going on in your engine, giving you a measurement in relation to what the experts in the petroleum industry have determined is normal or abnormal.

To see an example of an oil analysis report, click here.

Oil analysis gives you an excellent opportunity to get the maximum amount of life out of your equipment by monitoring the wear rate of your engine and detecting problems in the early stages.

Wouldn’t it be nice to know when to schedule an overhaul for your engine instead of having it out of service at the wrong time with a major problem? It would also be helpful to know that your engine doesn’t need an overhaul, regardless of the number of hours it has run.

How to read an oil analysis report
Contact the laboratory doing your oil sample and ask them for normal readings for wear metals, and fuel soot for your particular year and make of engine. You can also contact the engine manufacturer for the maximum allowable numbers for your particular engine.

As an example, let’s examine a typical 2006 500 horsepower, gas recirculation (EGR) diesel engine in a Class 8 truck running mainly highway miles. The numbers are for a 15,000-mile oil change without any additional bypass oil filtration.

  1. Let’s start with the viscosity. Viscosity is measured in centistokes (cSt). This is basically a reading of the amount of time it takes a volume of liquid at a given temperature to go from point A to point B – the thicker the oil the higher the number.


Typical 40 weight oil will run from 13 to 15. So, a good average number would be 14.5. If your viscosity is showing higher than 40 weight and you are not using any kind of additional oil additive, you need to check for a potential problem such as excessive soot, dirt or coolant.

You can easily determine this by seeing if there is a correlation between two different components of the sample. A very high soot reading, such as 4 or higher, can increase the viscosity. Positive antifreeze or high sodium is an indication of a potential trace of coolant in the oil and can increase the viscosity. High silicon from dirt can be because of clogged air filters, turbo or air system leaks.

What I see more often than increased viscosity is decrease in viscosity caused by fuel-related issues. Remember, the only thing that will thin your oil is fuel so if your viscosity drops from a normal 14.5 (40 weight oil) to 10.8 (30 weight oil), you need to have your injectors and or injector seals checked.

A typical sample will not show positive fuel in the oil unless it is excessive, such as 4 percent or more. So, some fuel can lower the viscosity but not alert the fuel in the oil parameter and show the sample is normal. I recommend taking the engine in and checking the injectors when you first notice the drop in viscosity instead of waiting for the sample to show positive fuel. By then your viscosity is really low and causing harm to the engine.

  1. Make sure the lab is doing a test for antifreeze, water and fuel in the oil. You always want them to show negative. If you ever show positive fuel or antifreeze, you need to get the engine off the road immediately and have it checked to prevent severe engine damage.

    Most of the time when I’ve seen positive water, but no antifreeze, it is because a dipstick seal or oil filler cap is loose or has a bad seal. When you pressure wash or drive through excessive rain, it can allow water to slip through and enter the oil. If it is only water and not coolant, it is probably not anything serious.
  1. Wear metals
    • Copper – less than 15
    • Lead – less than 15
    • Tin – 9 or lower
    • Chrome – 9 or lower
    • Aluminum – 9 or lower
    • Iron – 30 to 60

Iron is the main wear metal to keep an eye on when extending oil drain intervals. Many of the engine manufacturers allow up to 150 ppm on the iron with some up to 200. A good rule of thumb: The dirtier the oil, the higher the wear, and the higher the wear, the less engine life.

Remember this also: If a fleet is going 30,000 miles on their oil changes, without a bypass oil filter, they are typically trading their equipment every 450,000 miles. Have you ever talked with anyone who bought a fleet truck trade-in and had to do an overhaul at 600,000 because the cylinders were worn out?

There are ways to increase your oil change intervals without increasing wear by adding additional bypass oil filters with enough dirt-holding capacity to remove contamination and filter below 1 micron. Factory filters typically remove only down to 15 microns.

  1. Always keep a close eye on sodium levels to help find early stage coolant leaks. A typical coolant leak starts off small and slowly gets worse over time, almost like a leak in your ceiling at your house.

    I have saved countless engines by seeing a jump in sodium, such as 4 to 25, calling the customer, and finding the coolant leak early before the engine wear was affected.

    The lab would not red flag this sample because the sodium is below their parameter, but the jump should tell you something.

    See actual notes and lab report below. Notice how the sample goes back to normal after the engine is fixed. None of the samples showed positive antifreeze but only increases in sodium.

6-16-09- Rec’d sample, soot at 1.0, sodium 6 to 19, he will resample, mailed copy.

7-14-09- Rec’d sample, soot at 1.4, sodium 19 to 55, called customer, he will check and let me know, probably EGR cooler, mailed copy.

7-15-09- Found bad EGR cooler.

8-28-09- Rec’d sample, normal, soot at 0.6, mailed copy.

I’m going to skip many of the additives, but the three major ones are phosphorus, zinc and calcium. These additives are easy to see; just look for the large numbers. It is very common to see calcium numbers over 2000 ppm.

  1. The total base number – TBN – can help determine the amount of reserve additive remaining in the oil to help neutralize acid, much the same way we take a sip of that yucky chalky tasting antacid when our stomach hurts.

    The TBN will help keep the acid down and prevent corrosion and wear. Low TBNs generally mean not enough makeup oil is being added to replenish the additives, which will generally cause higher wear numbers and increase acid formation.

    The higher the TBN, the better – although the newer oils do not have as high a TBN because of the lower amount of sulfur in the fuel. I normally do not allow our customers to run their oil below a 4.5 TBN even though some engine manufacturers might let it go down to 3.
  2. The majority of contamination in a diesel engine is soot. These particles average below 1-micron in size and cause most of the normal wear inside the engine. A general rule: The higher the fuel soot reading, the dirtier the oil and the higher the wear.

    Many engine manufacturers allow up to 4 or higher fuel soot before changing the oil. I allow only up to 2.4 for our customers on typical EGR engines. By not allowing the fuel soot to go over 2.4, the oil does not get dirty and the engine lives longer, which is the primary goal of any owner-operator.

    As stated earlier, you can add bypass filtration to an engine and allow it to run much longer before the soot level and wear metals require changing the oil. The year, make and model of your engine will determine what the normal fuel soot numbers should be. Another example of just how different the numbers can be is a Cat non-EGR engine. The average fuel soot reading on a Cat is 0.2 to 0.4, and I will call a customer to change oil if the fuel soot level ever reaches 0.8.


Once you have chosen a credible laboratory to do your oil analysis and know what the normal numbers should be for your engine, it’s a matter of tracking each sample and looking for jumps in certain areas.

Find a good diesel mechanic who knows what to check on the engine when numbers go up on the sample.

Here are some good tips on troubleshooting potential problems based on abnormal numbers.

Here’s an example of high iron:

  • Feb. Iron 43
  • March Iron 39
  • April Iron 93

Something happened between the March and April sample that caused a major jump in iron. Run the overhead to make sure the valve clearances are within tolerance and valve timing is accurate. Check for any potential loose or broken part such as an adjustment bolt or injector spring etc. It may just be that the valves need adjustment.

If you don’t find anything, then drop the oil and inspect the pan plug for metal shavings from a potential broken or damaged gear. Typically, EGR engines will have higher iron numbers than pre-EGR, so it is more important on these engines to keep the oil clean with added bypass filtration. On a Cat ACERT with high iron, always check actuators and bolts.

High sodium but nothing else is a potential coolant leak. I normally start with the least expensive items to check and work my way up – internal leak on water pump, oil cooler, injector cup, air compressor, head gasket, liner leak or crack in liner.

On EGR engines the most common coolant leak with high sodium is the EGR cooler. If your sodium level goes above 25, go ahead and replace it before it begins leaking excessively which can damage bearings.

A report with high iron and sodium is not good news. It is usually liner related, and you will need to get the engine checked ASAP.

If you have high copper in Cat engines, but nothing else, it’s probably from a leaching process of the oil cooler and harmless. This is some kind of chemical reaction I have seen for years. I believe it started with the newer oil formulations for today’s higher soot engines. Usually if this is the case, you will see really high numbers like 300-500 ppm but you will also notice other wear numbers unchanged. I have also seen this on the newer Volvo EGR engines.

The important thing to remember is that normal oil cooler leaching will not harm the engine. If you see smaller increases in copper, such as from 15 to 33, it could be a potential rocker arm bushing. That would need to be checked. If this is the case, you will usually see an increase in iron at the same time.

Typically, on Detroit and Cummins engines you should not see high copper. But if you see copper numbers any higher than 15 on these engines, check the following: turbo, rocker arm pins, bushing, etc.

If you have more than copper go up, such as tin and lead at the same time, it could be a rod or main bearing, cam bearing etc, especially if the engine has more than a million miles on the original bearings. In that case, it would be good to go ahead and replace the rod and mains. If the copper goes away, you may postpone a complete in-frame.

High lead can come from problems with the air compressor, bearings or solder from oil cooler. If the high lead is from a bearing, it will eventually get into the copper and then you will have to replace them. Many of the newer engines no longer use lead in bearings; instead, a tri-metal overlay is used. I seldom ever see any issues with aluminum and chrome.

If you have high fuel soot, check the following: charge air cooler, clogged air filters, intake gasket, all connections going from turbo to engine (boots, clamps, and hoses), air line going from engine to intake of air compressor.

If no air leaks are present, check for leaking exhaust gasket or manifold. The turbo gets its boost from exhaust gas. If you are losing gas, the turbo may not build up the boost you need to get the right volume of air to the engine.

If there are no air or gas leaks, the problem would almost have to be fuel related. Check the injectors and remember that sometimes you can have an O-ring leaking fuel even though the injector passed the test on the computer. If this is the case, you will have to remove the injectors and reinstall with new O-rings. On high mileage engines, go ahead and replace all six injectors at the same time.

With EGR engines, sudden increases in fuel soot can be caused from problems with the EGR valves. If this is the case, many times you will have a fault code or see the engine belching black smoke. The most important thing to remember about high fuel soot is that it will decrease fuel mileage, which will have a major impact on your bottom line.

The great thing about oil analysis is that it may give you enough time to schedule getting off the road instead of being stuck out on the road with a broken engine.

One of the most important reasons to use oil analysis consistently is to find problems that can affect the performance and life of your engine.

All of these recommendations are based on what I have learned comparing real-world oil samples with real-world problems on diesel engines for more than 25 years. I hope this information will help those of you that want to learn more about the benefits of oil analysis.


Jerry Sims can be reached at or at 800-398-8114.