Let's look at oil analysis for our engines. First off, to make sure you're taking full advantage of oil analysis, you should examine your sampling procedure and ask if it is -----representative, timely and well documented. A sample of oil should be analyized shortly after it is taken since it will represent a point in time of the engine condition, and become less significant the longer it sits. Most laboratories recommend taking an oil sample while the oil is hot. This will assure dirt particles will not have settled out.
The oil sample should be taken from a source where there can be no contaminants that can enter the sample bottle. The best place other than a by-pass oil system return line is from the oil dipstick, using a plastic hose and a suction device. These can sometimes be obtained from the lab you use.
In most situations the real value of the data is in determining trends rather than in the accuracy of any one individual test. In general there are two different classes of analytical tests, those that measure the physical properties of the oil, and those that measure the level of contamination.
Physical properties are a good indication of the condition of the oil, and are often used to determine oil drain intervals. Some of the most common physical property tests are: viscosity, total acid number (TAN) and total base number (TBN).
Kinematic Viscosity (ASTM D-445) determined at 40 Deg. C and/or 100 Deg. C is a measure of the flow rate of an oil in relation to time, and is expressed in centistokes (cSt) 1 square mm/1 second = 1 cSt. This data is used to assign an SAE grade to an oil. Example: 40 grade oil has to fall between 12. 50 cSt @100 C minimum, to 16. 29 cSt @ 100 C maximum. Normally a 25% increase in viscosity is a warning that the oil is reaching the end of its useful life.
TAN (ASTM D974) determines the level of acidity by mixing in an indicator solution and then adding potassium hydroxide (KOH) until the solution changes color. The acidity is expressed as the milligrams of KOH required to neutralize a gram of oil (mgKOH/g). TBN (ASTM D2896) determines the level of alkalinity in an oil, which indicates the ability of the oil to continue to neutralize corrosive acids. The test measures the change in electrical conductivity. A higher TBN oil is considered better in neutralizing acids than a lower TBN oil. It is best to measure the change in TBN from new oil of the same type and brand you are using. The TBN of engine oil may be obtained from data sheets, or measured by analyzing a sample of new oil. Some manufacturers, such as Amsoil put the TBN number on the labels. A 50% reduction in TBN is a warning that the additives are becoming depleted and an oil change should be considered.
Common contamination tests include: water content, fuel dilution, and dirt ingestion and wear metals analysis. Water contamination can usually be detected visually, but a water content test (ASTM D1744)) is sometimes used as well. Fuel dilution is serious in that it can significantly reduce oil viscosity and increase engine wear. Since most engine oils gradually increase in viscosity over their useful life, a noticeable reduction in viscosity is a strong indication of fuel dilution.
Wear metals are metals used in the manufacture of the engine that will wear in normal use, such as Iron (Fe), Chromium (Cr), Lead (Pb), Copper (Cu), Tin (Sn), Aluminum (Al), Nickel (Ni), Silver (Ag). Analysis of the types and levels of wear metals can be used to determine which engine components are wearing and if the level of wear is becoming critical. Most tests measure wear metal levels spectrographically. The most common is emission spectroscopy. In this procedure a small oil sample is burned in a high temperature flame, and the equipment detects different levels of light emitted. The equipment is calibrated to simultaneously measure the emitted light from as many as 18 different wear metals and contaminants.
Another wear metal test called the atomic absorption analysis will provide the greatest level of accuracy for each element examined, but is more costly as well as time consuming as it requires one pass through the machine for each element tested.
Either of these two wear metal tests are expressed in (PPM) Parts Per Million by weight.
Dirt is probably the most common engine oil contaminent, and high levels can lead to excessive engine wear. The most effective way to detect dust or dirt contamination is to monitor silicon levels by spectrochemical analysis, though some tests can indicate total solids by centrifugal separation or filtering through a fine membrane filter. Contamination levels will vary according to the type of engine and the application, with off-highway equipment often having the highest levels. Again, it is important to measure the change in silicon or solids levels, rather than look at any individual analysis.
Each engine manufacturer has data on the "normal" wear of each of the elements for a given oil drain interval. Example. Cummins, Iron (Fe) 50, GMC 6. 2 Iron (Fe) 250, Mack Iron (Fe) 150. Remember in reviewing a report, ask yourself; is the elemental level proportional to the time on the oil? Example: 6,000 miles on oil, Iron at 25 PPM is OK for the above engines. 12,000 miles on the same oil, Iron at 40 PPM is still OK. 3,000 miles on the oil, Iron at 40 PPM would be poor. Still within limits, but poor.
Additive levels may also be measured with spectrographic metals analysis. Normal metals analysis will detect the levels of zinc, phosphorous, calcium and barium, which are common elements in most additive packages. A 50% reduction in parts-per-million of these elements indicates the oil should be changed.
Most labs will compare the wear trends to similar operations using the same type equipment in order to more reliably predict component failure. Because of this, it is important and valuable to work with a lab that has years of experience, as well as hundreds of thousands samples in their files to compare data.
Periodic oil analysis is an important element in extending oil drain intervals and prolonging engine life, however looking at trends is the best solution to achieving this.
Wayne
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94'SLT 4X4 AT/White in color. Factory Tow Hooks & Running Boards. Amsoil By-Pass filter, Amsoil Air cleaner,and all fluids are Amsoil. Optima "Red Top" batteries.
BD exhaust Brake, BD Torque Lock, BD Torque Converter, Dr. Performance Stage II Injection Pump. Mag-Hytec Diff Cover,Mag-Hytec Transmission Pan, Isspro Pyro, Boost,Oil temp Gauges mounted in 3 Gauge post mount. One gauge monitors Engine Oil, Trans, Diff. Temps.
Wayne Owen
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