One Eastern company has used oil analysis to extend crankcase drain intervals, saving over 3,000 gallons of oil per year and several thousand dollars in reduced labor for oil changes. A Midwest truck fleet operator has increased drain intervals to 50,000 miles for most equipment, and has gone to no-drain for Detroit-Diesel engines. Samples are taken every 8,000 miles, and 97% of the equipment makes it to the higher drain interval. The other 3% are detected early and changed when needed.
Thousands of other commercial and industrial operators have benefited just as much from independent oil analysis. And benefits often involve more than just an increased oil drain interval. Wear metal and contamination levels are good indicators of equipment condition, and can provide early warning of future problems. High metals content can indicate unusual wear, and even help locate what component is wearing out. And high levels of water/coolant or dirt can indicate cooler leakage or air filter failure, before these can cause serious mechanical damage.
To make sure that you're taking full advantage of the value of oil analysis you should examine your sampling procedure and ask if it is representative, timely and well documented. A good sample must be representative of the oil in service if the data is to be meaningful. Samples should be analyzed shortly after they are taken since they represent a point in time of the engine condition, and become less significant the longer they sit. And a sample must be documented fully to describe what the equipment is, the oil type, operating conditions and interval from previous sample. Without this information, a valid comparison can't be made.
Most laboratories recommend taking an oil sample while the system is operating or shortly after shutdown. This will insure that wear dirt particles will not have settled out, and that water or coolant have not yet separated. A sample should be drawn from a properly located sample valve when possible to avoid the need to dismantle lines or open up the reservoir. If a system has a sample valve it is often found on a low pressure return line, usually just before the line connects to the reservoir. A sample drawn from that valve is often the most representative of operating fluid condition. One exception would be samples that are to be analyzed for particle count or wear metals. These should be drawn upstream from filter elements if at all possible.
Prior to sampling, the valve should be wiped clean so that surface dust and dirt will not accidentally fall into the sample container. This step is of particular importance if the sample is to be analyzed for wear metals or particle count.
If a sampling valve is not available, the next best place is the reservoir itself, again, either during operation or just after shutdown. The sample can be drawn through a plastic tube, with any of several sample-taking devices (AMSOIL Product Code G-1206 Oil Analysis Pump is available for $24.50). The sample should be taken from the middle of the reservoir to make sure it is representative. Sludge, dirt and water will collect on the bottom and sampling there will give the impression that the circulating oil is in poorer condition than it really is. If the drain plug in the reservoir is the only place you can take a sample, be sure to flush at least a pint of oil out before taking a sample. This will remove most of the sludge, dirt and water before the sample is taken.
The sample container is as important as the sample itself. Old paint or coffee cans may be great for paint thinner, but they just won't work for oil analysis. Sample containers are available from the oil laboratories, and sometimes from the oil venders as well. In either case, it is important enough to keep several empty containers on hand so that there is never a need to use anything else. One note of caution, some sample containers are not compatible with synthetic lubricants, causing them to soften and sometimes dissolve. Be sure to advise the oil lab or oil vender what type of oils you will be sampling so that they can be sure you have the proper container (AMSOIL Synthetic Lubricants are compatible with the same type of sample container used for petroleum lubricants. Oil Analyzers, Inc., Sample Kits [G-1318] are available through AMSOIL for a retail price of $18.50).
Since an oil sample indicates the condition of the oil and the equipment at the time it is taken, it is important to promptly send it in for analysis. Normal mailing and testing will take 3-10 days. Delaying the sample will only make that period longer and the results that much less significant. Most labs provide convenient pre-addressed mailing cartons, making it easy to mail the sample the same day that it is taken.
Making sure that the sample is labeled properly is an important third step. Sample date, equipment sampled, operating hours or miles since the previous sample, oil type and any unusual operating situations should be noted either on the sample container or a sheet of paper included with the sample. To provide a basis for comparison, a sample of new oil or a sample taken just after an oil change should be sent for analysis. If the same oil is being used in several pieces of equipment, only one new oil sample is needed for a base-line.
Most important, be sure that your company name, address and telephone number are included with each sample. Most labs get hundreds of samples each day, and after a while they begin to look very similar. You should include the name of someone who is to be called if there are indications of serious equipment problems, or if the oil needs to be changed.
An important aspect of oil sample analysis is the importance of the equipment being sampled. A large bearing on a 10-cylinder diesel is much more expensive to replace than the main bearings on a gasoline engine. An oil analysis program should take into consideration the cost of equipment repairs and downtime, and the importance of that particular equipment in the overall plant production cycle. Critical equipment may warrant specialized oil analysis testing that would not be cost effective on less important equipment.
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. The 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). The level of contamination is important in identifying equipment malfunctions such as radiator leaks or damaged air filters, and in determining equipment wear rates. Common contamination tests include: water content, fuel dilution, particle count and wear metals analysis.
Although oil analysis may include engine oil, hydraulic oil, gear lubes, and many other fluids, we will concentrate our discussion on engine oil, but many of the same features of engine oil analysis extends to other fluids. Periodic engine oil analysis is an important element in extending oil drain intervals and prolonging engine life. Rising prices for motor oils and questions of future availability have made it increasingly important to extend oil drain intervals whenever possible. Periodic analysis is the only reliable method to determine exactly when the oil needs to be changed. In addition, analysis of the types and levels of contamination can identify potential engine problems before they become serious enough to cause downtime and major repairs. An effective engine oil analysis program should include the following tests.
Viscosity -- One measure of the degradation of a motor oil is its viscosity, often measured in centistokes (cSt) at 100 deg. F. As petroleum based motor oils break down their viscosity increases (becomes thicker). Normally a 25% increase is a warning that the oil is reaching the end of its useful life. Synthetic or partial synthetic base motor oils also increase in viscosity when they degrade, but the rate of increase is usually much slower. Fuel dilution can cause a reduction in viscosity and should be monitored as well. In most cases, however, additive depletion or contamination will be the factor determining oil change interval.
Total Base Number -- Most motor oils are formulated with a variety of additives that enhance lubricity, retard oxidation and corrosion, improve viscosity characteristics and pour point, and reduce the tendency for sludge and deposit formation. The level of additives can be determined by measuring the total base number (TBN) of the oil, usually expressed in mgKOH/gm. Since there are many different oil formulations, it is best to measure the change in TBN from new. The TBN of the new oil should be listed in the data sheets, or can be obtained by sampling the oil just after an oil change. A 50% reduction in TBN is a warning that the additives are becoming depleted and an oil change should be scheduled.
Coolant contamination -- cooling system leakage is one of the most serious hazards for engine lubrication. The water reduces lubricity and causes corrosion of metal parts. The glycol from anti-freeze breaks down at high engine temperatures and forms sludge and deposits. In most cases analyzing for water content is not reliable enough, as high engine temperatures can vaporize water quickly and keep detected levels as low as 0.05 percent. One alternative test measures the level of glycol in the oil, while emission spectroscopy will detect levels of boron or sodium from the additives in antifreeze. In either case, once coolant leakage is detected, the leak should be repaired and the oil changed.
Wear metals -- 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 levels of iron and aluminum to determine the amount of wear in piston rings and cylinder walls. High levels of copper, lead and tin are indications of main bearing wear and represent a more serious problem. Some tests also determine the level of silicon as a measure of ingested dirt or dust, the levels of lubricant additives and the levels of sodium or boron which indicate contamination from antifreeze.
In some instances this information has made the difference between minor component repairs and major engine overhauls. Often there is a distinct correlation between contamination or additive depletion and increased wear metal content, making it relatively easy to not only isolate the problem, but recommend specific action as well. Analytical techniques include atomic absorption, emission spectroscopy and Ferrographic analysis, with each technique offering a slightly different perspective on wear metals.
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