RECENTLY, I WENT to the doctor for my annual checkup. Before the office visit, I had some bloodwork done to determine if my medications were effective, if there were any interactions, and if I had any ailments that were starting to make their presence felt.
As I was waiting to be tested, I realized that modern medicine has caught up with trucking technology. Or is it the other way around?
In trucking, we've been examining used fluids for more than a quarter century. Analysis is an excellent tool for determining the health of a component and to project future wear.
Just as blood analysis determines how your organs are functioning, used oil and coolant analyses tell you how your engine is doing. These tests indicate how much life remains in the oil by measuring reserve alkalinity, the total base number (TBN), or acidity expressed as total acid number (TAN). One rule of thumb is that as long as TBN exceeds TAN, the oil is still usable. The difference between TBN and TAN roughly indicates how much longer it can be used.
Viscosity also determines remaining useful life. As oil is used, polymer viscosity improvers undergo mechanical shear. When oil loses viscosity to the point that film strength is diminished, oil must be changed.
Dirt and contaminants affect oil's performance. Changes in the amount of silicon in oil could indicate if dirt is present. This is especially important for producers with trucks that operate off paved roads. But high silicon can also come from other sources, such as RTV gasket material. Oil analysis results are best when used to indicate what to look for, not absolute indicators of problems.
Soot in oil is a product of improper or incomplete combustion or leaking exhaust gas recirculation devices. It can also contribute to excessive component wear. Essentially, incompletely burned hydrocarbon fuel can be an abrasive. As such, it acts like a lapping compound carried by the oil, wearing all moving parts.
Identifying worn parts
Oil analysis can often identify parts that are starting to wear. After checking for viscosity, soot, dirt, and TBN/TAN, examine if any metals are wearing excessively. Alone or in combination, they can often identify which parts are wearing out.
For example, in a diesel engine, iron and chromium might be elevated. They could indicate piston ring or turbo-charger shaft wear. With high iron but normal chromium, it could be cylinder liner, valve train, or crankshaft wear.
Lead, tin, and copper often indicate bearing wear. They could also be from oil coolers or turbocharger bearings. More detail is available in the TMC Recommended Practices. What holds true for Class 2-6 vehicle alerts listed in RP1420 also holds true for ready-mix trucks.
There are two ways to analyze and interpret fluid analysis results: set limits and trend analysis. When your analysis provider, either an oil supplier or independent laboratory, reports that oil is good to use or is out of specification, they use set limits. For every element or property they examine, they have set limits for warnings and alert values. For example, if the warning level for iron is 100 parts per million (ppm), 99 or below indicates the oil is good; 100 or more will generate a warning message.
Trend analysis also uses set limits, but once trend lines are established, deviations from those trends generate alerts. For example, if iron, measured at 15,000-mile intervals, reads 52 ppm, 48 ppm, 55 ppm, and 88 ppm, the last reading would not affect a set limit report, but it is a sharp deviation from the trend. The deviation would trigger an alert to further investigate.
Paul Abelson is a former director of the Technology and Maintenance Council of the American Trucking Associations and is on the board of the Truck Writers of North America. E-mail firstname.lastname@example.org.