Down to a science

| June 07, 2008

A precise report that reveals exactly how much of a certain metal is in your oil is nearly useless unless the lab knows exactly what model engine you have. An amount of a certain metal that may be perfectly normal in one engine could be a sign of serious trouble in another.

Oil analysis ensures you’re changing your oil at the right interval and warns you of developing trouble. Owner-operator Charlie Flexter, who hauls grain in often heavy central Illinois traffic, says oil analysis found that his conservative 15,000-mile oil change interval was actually too long for his Cummins engine, and he went to 12,000-mile intervals.

On the other hand, when using the latest, high-quality CJ-4 oils and running relatively new engines, truckers who drive over-the-road and don’t idle much can often safely use analysis to extend changes, in some cases to 30,000 miles or more. Why throw good oil away?

Experts from several refiners made it clear to us that oil analysis is a science. Unless you know a little about that science and how to make it work for you, you won’t be getting the full benefit of oil analysis.

Filling out the sample form
Something as simple as correctly filling out a form can have a big impact, says Lilo Hurtado, CVL applications engineer at ExxonMobil.

“People do not always take the time to fill out the form that comes with the sample properly,” Hurtado says. “It makes a huge difference.”

Shawn Ewing of ConocoPhillips Lubricants says, “Timely and accurate information is first and foremost when it comes to a good analysis report. When better information is provided to a lab, better results will be returned.”

BP Castrol Technology Manager Steve Goodier says, “Without the proper information on the form, the result can be absolutely meaningless.” He says that BP Castrol’s service, Lab Check, uses an online system that allows the fleet to create a form for each vehicle so that all the information that doesn’t change only has to be filled in once, which helps avoid errors.

Hurtado recommends you make sure to put all these items on the form and check that they are correct:

  1. Engine make and model number, as well as all other equipment information.

  2. The date when the sample was taken.
  3. Oil name and refinery brand.
  4. The viscosity of the oil, for example 15W-40 or 10W-30.
  5. The miles (or hours for off-road trucks) since the last oil change.
  6. The miles on the engine since the last overhaul.

Walt Silveira, Shell Lubricants’ North American technical manager, recommends including the amount of makeup oil added since the last change. Keep a record of how much oil you add and put the total on the analysis form.

Silveira also says an independent lab should get a sample of the oil right out of the bottle. This is even better than having them read off the oil data sheets, because the sheets show only typical values of items like additives, rather than the actual values in the oil you used.

It’s also vitally important to make sure the sample is pure. Goodier says Lab Check provides new sample bottles for each sample. Merely cleaning out the old bottle with diesel fuel may not remove every trace of material from an earlier sample.

The whys
Including the date and other equipment information along with the miles since the last change will help keep samples properly identified – thus, they won’t be confused with one another. This would help, say, if you had three trucks with C-15 engines and you always changed their oil at as close to 25,000 miles as possible.

The engine make and model number is critical because, says Hurtado, “Every engine make and model has a certain metallurgy. What is acceptable for one engine may not be acceptable for another.” One of the most critical things analysis measures is wear metals, and unless the lab knows what should and should not be there, any results will be meaningless. The manufacturer might even have made a minor running change in the piston, rings or cylinder liner that would show different wear metals even under ideal conditions.

Silveira says the lab needs to know what engine you’re using because they need to know not just what kinds of metals are typical but at just what point higher than normal levels mean there’s an engine problem or the oil needs to be changed. Having the sample of fresh oil enables the lab to know, for example, what additives they should find in the oil and how much of each should be in there. Having the sample date and the name and refinery brand of the oil helps them identify the proper fresh sample from the many they may have on hand, so they know where all the additive levels and other parameters started out.

An oil’s viscosity can go up or down, depending on operating conditions and how much soot, fuel or antifreeze may be getting into it. Having the viscosity number of the oil will allow the lab to determine how far the viscosity or thickness has strayed from the initial level. For example, the thinner viscosity of a healthy 10W-30 oil would be typical of a 15W-40 oil that had seen serious abuse from a factor such as fuel dilution or heat.

Miles since the last change is critical. Metal will steadily build up in the oil until it is drained, so you can’t tell how well the oil is working without knowing the mileage. Even if the oil is still maintaining an ideal, minimal rate of wear, if it’s been in twice as long, the level of each wear metal will be twice as high.

The total miles on the engine is critical because, as Silveira says, “in older engines, we see iron and copper in significant amounts that may increase as the engine gets older, but these amounts are still normal.” In other words, the rate and type of wear inside the engine will change as it ages even when the lubrication is perfect and there are no mechanical problems. A good example of this is the fact that new engines sometimes get extra copper from the oil cooler until it breaks in and develops an oxide layer (like an aluminum coffee pot). If the lab does not realize the engine is brand-new, they may flag something perfectly normal as a problem.

Knowing how much makeup oil was used is useful because such parameters as TBN and viscosity will change more slowly if the engine is continually getting new oil. Continuing to supply additives and oil not yet exposed to heat or dilution by combustion by-products may mean the oil can stay in longer.

Reading results
Working with a reputable lab that includes interpretation is essential. It does not make sense to get a report full of accurate numbers without having expert advice to help you understand exactly what they mean. ConocoPhillips’ Ewing says it’s pretty simple to evaluate the data. “Most labs will clearly highlight the items that need to be addressed.” They normally give descriptions of the problem’s extent to “provide direction for corrective action,” he says. “To effectively read the report, notice what is flagged and use your judgment based on your fleet’s prior history.”

If an item is marked as critical, the lab is more than likely to discuss this issue with you. “It may require immediate action,” says Ewing.

Silveira suggests establishing personal benchmarks, goals and priorities when doing analysis. “Are you trying to determine just when to change?” he says. “Or is your primary goal to optimize your maintenance?” He stresses that you should read the comments completely. “Then get in touch with Shell or your other supplier to ask for their advice.”

Hurtado stresses the need to look at the results as creating a trend. “This means you need to convert how much metal you are getting to a rule of thumb,” he says, “like so much of each wear metal per 5,000 miles. If the curves are flat, everything is fine. But if there is an increasing trend, the oil is inducing some wear.”

For example, if you were normally getting 250 grams of iron per 25,000 miles and the iron suddenly rises to 300 or 350 grams in that same 25,000 miles, you have a problem. This rising trend means you either need to change the oil a bit earlier or you have a mechanical problem.

BP Castrol’s Steve Goodier agrees: “The big thing is to really look at it as a trending process. Every parameter has variability, and you need to understand what any change in a number actually means. Any oil analysis process is only as good as the interpretation.”

Goodier says large fleets get their interpretation from Lab Check via a personal call or visit from a fleet engineer assigned to them. Even small fleets get interpretation via the lab’s website, where the experts interpret what’s in the report in detail, translating all the numbers and technical terms into plain English.

If you can learn to read the report yourself, or can get your lab’s representative or oil supplier to interpret the numbers as in the example above for you, you can make the most of oil analysis.


Oil Analysis Dictionary
TBN stands for Total Base Number and refers to additives that behave like Alka-Seltzer, as Silveira puts it, or simply “acid-neutralizing additives,” according to Hurtado.

TAN stands for Total Acid Number, and it “reflects the amount of acid in the oil,” Ewing says. “TAN represents … materials such as organic acids and oxidation products.” Acids come either from sulfur in the fuel as it burns or from oil when it gets hot and breaks down. They weaken metal and greatly accelerate wear. But when exposed to certain additives, they are “neutralized” through a chemical reaction. This changes them into something that is not an acid and will not weaken metal.

There is a point “where the TBN and TAN lines cross,” says Silveira. As the oil accumulates more and more acid, and the TBN is gradually depleted, you reach a point where there is just enough TBN to neutralize all the remaining acid. Change the oil at or before it reaches this point.

Because ULSD has much less sulfur than earlier fuels, the amount of TBN and TAN in the oil at the point when it needs to be changed is, today, much lower than it was when burning earlier fuels, Silveira says, but the engine remains fully protected.

Viscosity, says Hurtado, is a “measure of oil’s resistance to flow.” Ewing describes this as a measurement of the “thickness” of the oil and says that ConocoPhillips believes it to be the most important property to measure. Hurtado agrees. “In general,” he says, “if the viscosity is maintained within the specified range, the oil will perform its role as a lubricant.” Fuel dilution, for example, can cause the viscosity to be too low (the oil too thin), while being in the engine too long can make it too thick. It can also be thickened if antifreeze is leaking into the oil because of a chemical reaction, says Silveira. “Both extremes of viscosity can cause premature wear,” concludes Ewing.

The more common direction with diesels is for the oil to thicken. This, says Silveira, often happens when soot content reaches excessive levels.

Soot loading refers to the oil’s ability to keep soot dissolved. Some soot always gets into the oil. Soot from imperfectly burned fuel, and from oil starting to decompose, gets into the oil at the top of the cylinder liner and is scraped down into the oil pan, says Hurtado. Soot loading is measured as a percent of the weight or volume of the oil.

Soot is a significant problem with the latest engines. They send more soot into the oil near the top of the cylinder liner. Too much soot increases the viscosity of the oil so it won’t flow properly to all the parts, and can make it abrasive, directly causing wear. Silveira says soot’s handled by additives, “so it won’t plate out and cause sludge.” He says there are different ways to check on soot and it’s smart to make sure the lab checks the level using the same method every time.

Wear metals refers to measurement of the actual amounts of metals, such as iron, nickel, chromium, aluminum and tin, that are worn off various engine parts into your oil. Wear metals is one of the most critical measurements. It gives the true bottom line – how well the engine parts are actually being protected. The same test measures silicon, which is normally dirt from an air cleaner that’s not functioning properly and can damage the engine, as well as items such as sodium and potassium that can indicate a coolant leak into the oil.

Additives refer to items like calcium, magnesium, zinc, phosphorous and other minerals that protect the engine. They help tell you whether or not the oil is holding up.

Fuel dilution tells you whether or not you have fuel leaking into the oil from bad injectors. This test is normally not run unless triggered by low viscosity. Discovery of fuel dilution will often save you from replacing at least one cylinder kit (liner, piston and rings and connecting rod and bearings).


For more information:
BP Castrol
(800) 255-4417
www.castrol.com

ChevronTexaco
(925) 842-1000
www.chevrontexaco.com

ConocoPhillips
(800) 255.9556
www.conocophillips.com

ExxonMobil
Exxon: (800) 443-9966
Mobil: (800) 662-4525
www.exxonmobil.com

Lucas Oil
(800) 342-2512
www.lucasoil.com

Shell Oil Co. U.S.
(713) 241-6161
www.shellus.com

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