Extreme Duty Oil

Melvin Joseph Construction runs a fleet of construction equipment which includes a Ford L9000 dump truck with a Caterpillar 3406E diesel engine. The truck is used primarily in a sand and gravel pit operation, with secondary use in a power plant with coal-ash laden air. Loads average 70,000 pounds for the vehicle. The truck logs many hours' idle time, and virtually all its travel is stop and go. Caterpillar recommends 6,000 mile drain intervals for this engine in this service.

In August, 1996, AMSOIL Series 3000 Synthetic 5W-30 Heavy Duty Diesel Oil and the Dual Gard By-Pass Oil Filtration System, with a pair of BE-110 filter elements, were installed, when the vehicle had 16,300 miles on it. It now has 144,472 miles on it with 128,172 miles on the oil since the last change. (Full flow and by-pass oil filters have been changed at engine and filter manufacturer recommended change intervals.) That drain interval is 21 times the recommended oil change interval . . and the oil is still in use.

How's the truck doing? It consistently obtains 7.5 mpg fuel mileage in an application in which fleet supervisor Melvin Joseph Jr. says 6 mpg would be "somewhat of a miracle." The unit's 100 deg. C oil viscosity varies less than two percent, remaining in the middle of the SAE 30 range. Though the truck operates in exceptionally dirty, dusty conditions, regular trend-lined oil analysis shows its percent solids have never exceeded 1.1. The condemnation limit for the engine is 2 percent.

What are condemnation limits and what do they mean? Oil condemnation limits are set by engine (or component) manufacturers as a yardstick against which to judge the ongoing serviceability of the lubricant and to evaluate the well-being of the engine or component. The condemnation limits for physical properties, such as percent solids, and oil degradation, such as TBN, are absolute. That is, when a sample of used oil reaches or surpasses one of these limits, the oil must be changed. It is no longer fit for continued service. The quality of solids it contains, for example, is potentially harmful to the engine.

Condemnation limits are related in the spectrographic analysis portion of an oil analysis report – the wear metals. They are expressed as parts per million of a chemical element per specific distance. For example, the condemnation limit for the wear metal copper for the Caterpillar 3406E engine is 16 parts per million (ppm) over 6,000 miles. Generally, oil drain intervals mileage and condemnation mileage limits are the same, as they were for this engine.

Why aren't these limits absolute as the percent solids or TBN limits are? Because these limits are not used to evaluate oil serviceability. Instead, they provide a "window" on engine well-being. Wear metals levels higher than condemnation limits indicate potential engine problems.

In fact, the metal particles detected by spectrochemical analysis (the method used to evaluate wear metals content) are far too small to damage components. They are "wear" metals because they indicate that wear is occurring in the engine, not because they contribute to or cause wear. In fact, sepctrochemical analysis is blind to metal particles large enough to cause wear. Such particles are simply too big for the test apparatus and procedure to handle.

Wear metal condemnation limits are virtually meaningless for oils in extended drain service. Condemnation limits converted into wear metals/miles (ppm/mile) are useful tools for evaluating extended drain oils, however.

For example, the oil in the dump truck had been used, at the time of this writing, for 128,172 miles. The oil's high value for the wear metal aluminum was 6 ppm with condemnation at 16 ppm. In ppm/mile, aluminum reached approximately 0.00025, with condemnation limits at 0.00266 ppm/mile. Its high for lead was 10 ppm with condemnation at 40 ppm. For lead, the sample's high was virtually undetectable, with condemnation limits at 0.00683 ppm/mile.

The scenario looked different for wear metals iron and copper. Condemnation limits for iron were 54 ppm based on a 6,000 mile interval, which equals 0.009 ppm/mile. The sample's high, reached at 96,422 miles on the oil, was 200+ ppm. The oil first exceeded the 54 ppm iron condemnation limit at the 13,015 mile sampling. However, at 0.0065 ppm/mile, the oil never exceeded to per-mile limit of 0.009 ppm/mile.

The cooper level reached a high of 475+ ppm at 13,015 mile sampling, with a condemnation limit of 16 ppm over 6,000 miles. That translates to about 0.037 ppm/mile with a condemnation limit of 0.00266 ppm/mile.

How should the iron and cooper reports be interpreted? Let's look at the iron numbers more closely. The oil first exceeded the limit when it had been in use for more than double the miles at which the limit was set, and the value in ppm/mile never exceeded the limit.

In fact, the iron content was traced to a injector problem called ring wipe, which is not oil-related.

It was a different story with copper. The oil exceeded the condemnation limits, 16 ppm at 6,000 miles (0.00266 ppm/mile), virtually from installation, reaching a high of 475+ ppm (0.035+ ppm/mile) at 13,105 miles. After peaking, the copper value declined steadily, dropping below the 6,000-mile condemnation limit at the 112,912 mile sampling.

The independent analysis lab and the fleet supervisor treated the high copper level as an idiosyncrasy of this engine – something to be watched, but not something to warrant engine teardown or even an oil change. Why? Impending failure or sever wear would have shown multiple high wear metal levels. For example, this engine's bearings have layers of tin and lead over the copper. The lead and tin levels would also have been high in the sample if a bearing were in trouble. Additionally, the subsequent drop in copper level proved the lab' and supervisor's wait-and-see approach prudent. Nothing was wrong with the engine or the oil, even after 13,015 miles; that's why the copper levels dropped. The oil, of ourse, is in continued use after 128,172 miles, and the engine is still going strong.