Understanding the Nature of Lubricating Oil
The concept that oil "breaks down" or "wears out" over time is inaccurate. Oil does not "wear out"; it just gets dirty. In order to combat contamination, oil companies have worked diligently to enhance oil and lubricant products to better meet engine manufacturers' ever increasing requirements.

Just look at what has happened over the past fifteen years in regard to oil drain intervals. Fifteen years ago, typical recommended oil drain intervals for a 300 horsepower heavy-duty diesel were around 8,000 to 10,000 miles in an over-the-road truck. Today, the same trucks typically have 425 to 450 horsepower engines, yet the oil drain intervals have increased to 15,000 to 25,000 miles.

The same quality crude oil base stocks that were used 15 years ago are used to make today's oils, yet these lubricants last twice as long as they did fifteen years ago. The reason for this increase can be found within the higher-quality additive packages currently used. As additive (or detergent) packages continually fight against contaminants, the petroleum base of oil lube is left protected. Over time, however, as they fight against constant contamination, additive packages will become depleted. High quality (typically bypass) filtration has become the primary method to combat the depletion of the additives within new oils.

Soot, a Primary Enemy
Soot has long been an industry demon, but the total affect on the environment and on our engines has been difficult to quantify.

NASA scientists from Goddard Institute say soot, mostly from diesel engines, is causing as much as a quarter of all observed global warming by reducing the ability of snow and ice to reflect sunlight. In addition, several SAE papers have shown how soot contributes to diesel engine wear. One of these papers quantifies how severe the affect of soot in today's engines is. According to COMO paper EX1, soot will enter the lubrication oil at the rate of .0048 oz for every gallon of fuel burned.

A large truck will burn 1,786 gallons of fuel every 12,500 miles, at 7 mpg. During this 12,500-mile interval, more than half a pound (8.75oz) of soot will enter the oil!

Full-flow filters are not designed to remove small contaminants. Engines that are only equipped with full-flow filters are designed to remove and control particles 40 microns and larger. Standard full-flow filters are designed to be porous enough to allow high flow rates of oil through the engine and are intended only to protect the engine from large particles that could damage vital parts.

Since the majority of soot particulates created within the engine are 10 microns or smaller, they will easily pass through the full flow filter element. The typical flow rate for a full-flow filter within a diesel engine is 15 to 20 quarts per minute. To remove the smaller particulates, full-flow filters would need to reduce the pour size of the filter elements and, in turn, flow rates would be reduced. If the full flow-filter were to slow the flow of oil, then the engine would be starved of lubrication and would overheat and seize.

New Laws- New Environmental Concerns- New Engines - New Problems
EPA requirements have forced the diesel industry to consider new ways to meet more stringent emission standards. In response, the industry has developed a new technology and adopted a new three-letter word, EGR (exhaust gas re-circulation).

Engine manufacturers have developed EGR engines to meet EPA emission standards. Although these newer engines emit less contamination into the air, higher carbon soot levels are being detected within the engine and engine oil. In March 1998, at API's Lubricants Committee meeting in San Francisco, as reported in Lubes & Greases magazine (May '98), John Graham of Cummins Engine Co. had the following comments about the impact of EGR on diesel: "Diesel engine manufacturers face the prospect of having to reduce their drain interval recommendations significantly because of increasing levels of soot, caused by the need to introduce EGR."

EGR exhaust is cooled and re-circulated though the engine in order to reduce oxygen concentrations within the cylinder thereby lowering flame temperature and nitrogen oxide (NOx). Soot and fuel sulfur oxides are critical issues with EGR. Mr. Graham noted that a dramatic decrease in oil change intervals to, say, around 10,000 miles would be needed to address the additional contamination.

Instead of trying to solve this problem of higher soot levels by adding additional filtration, engine manufacturers and oil companies are relying on "new" oils to solve this problem. Admittedly many oil companies have introduced EGR type oils that allow users of EGR engines to maintain old service standards, but have had to increase the soot and other contamination fighting additives to do so.

Next week we'll look at additional issues as well as a feasible solution... stay tuned.