For almost 20 years, the thirst for more capable lubricants has been unquenchable. Every time new environmentally-mandated rules change, so do the engines and what they require of oils that protect and cool their moving parts.

The latest classification is CI-4 Plus, formally adopted by the American Petroleum Institute (API) late last year. CI-4 Plus is an enhancement of the CI-4 rating that took effect in September 2002 as diesel engine manufacturers were preparing to introduce powerplants with tight new pollution controls.

Indeed, CI-4 Plus is not a radical new development — many premium lubricants formulated for CI-4 already comply with the requirements of CI-4 Plus — but it acknowledges a variety of concerns that have arisen after two years of experience with engines that use cooled exhaust gas recirculation (EGR) to reduce nitrous oxide and other harmful emissions.

In the lab and in limited field trials, engines equipped with EGR, retarded timing, and high top piston rings ran far hotter than their predecessors. They also required more oil to run and burned off less during combustion. For engine oils, it added to an already heavy workload.

Heavy-duty engine oils are true multi-taskers, and no job is less important than the others. They lubricate and cool the engine’s moving parts, and act as a sealing agent between the cylinder walls and the piston rings to ensure proper compression and reduce blow-by or exhaust gasses from entering the crankcase. They hold particulates in suspension, so when you drain the oil, contaminants like soot and sludge go with it. And they protect parts against corrosion and neutralize harmful acids in the crankcase.

Anticipating greater soot loads and shearing (the breaking down of the oil’s polymers and therefore its ability to hold on to its viscosity or thickness) in engines with EGR, the API established CI-4 as its new benchmark for dispersing soot, controlling oxidation, and neutralizing acidic byproducts of the combustion process.

But when most heavy-duty diesel engine manufacturers agreed to comply with Tier 2 emission regulations by October 2002 — 14 months ahead of schedule — in order to settle a dispute with the U.S. Environmental Protection Agency and the California Air Resources Board, it left little time for anyone to test engines in real-world conditions. In some cases, the engines didn’t hit the streets until after the CI-4 oils did.

Within a year, there were five new specs from engine manufacturers requiring some aspect of performance beyond what the CI-4 category requires. And like the engine manufacturers themselves, the tests weren’t necessarily in harmony with one another.

For example, Caterpillar said the sulphated ash used to neutralize acids in the oil could contribute to the formation of deposits on the upper pistons of engines that use ACERT, a proprietary emission control system that does not use EGR. The deposits were significant enough that the company issued a new oil spec in May 2003 called ECF-1 that limits the ash content to less than 1.5 per cent.

Mack, meanwhile, replaced its EO-N Premium Plus specification, issued in 2002, with EO-N Premium Plus 03 after seeing more soot than expected in its internal and cooled EGR engines. Soot causes oil to thicken, shear, and lose viscosity. How do you traditionally improve the soot-handling characteristics of engine oil? Boost the ash content – in direct contrast to Cat’s recommendation. Ashes and other metallics in oils can have an adverse effect on exhaust catalysts.

The situation led refiners to call the conflicting requirements significant engineering challenges — particularly, how to limit ash without making additive packages too weak to be effective. A strong additive package is needed to make oil less likely to shear and turn thick, which can cause plugged filters and cold-start problems.

For truck owners, it emphasizes the need to shop carefully, especially if you’re intent on extending oil-drain intervals. Not all engine lubricants are the same; you should check with your engine manufacturer to find out what to look for in an oil.

Premium engine oil starts with a high-quality base stock that’s exceptionally free of impurities — highly refined petroleum oil, a synthetic, or a blend of the two. It’s then fortified with chemical additives like metallic detergents to reduce high-temperature deposits; soot dispersants; film-forming anti-wear agents; oxidation, rust, and corrosion inhibitors; anti-foam agents; pour-point depressants to help the oil flow in cold temperatures; and viscosity index (VI) improvers. The oil will have a Total Base Number, or TBN, indicates the additive package’s ability to neutralize acids.

The VI number is a measure of the relative change in viscosity of oil over a temperature range. The higher the viscosity index, the smaller the viscosity changes over temperature. The VI is not related to the actual viscosity or SAE viscosity, but is a measure of the rate of viscosity change. Generally, multigrade oils (0W-40, 10W-30, etc.) will have high viscosity indexes; monograde oils (SAE 30, 40, etc.) will have lower viscosity indexes.

Even though it’s not considered an entirely new standard, the establishment of CI-4 Plus has given fleet owners confidence that a single category of oil that will meet most of the manufacturer-specific specs and be backward compatible with other API ratings and earlier generations of engines.

It may be the last engine oil rating to achieve the feat. The next classification, Proposed Category 10, or PC-10, is scheduled for next year, before even tougher emission regulations from the EPA take effect. Engines that use cooled-EGR to meet the 2007 standard will route even more exhaust gas through the engine, use aftertreatment filters to trap and burn up particulate matter, and run on ultra-low-sulfur diesel fuel — 15 parts per million compared with 500 ppm today.

The environment will be a harsh one for engine oils, especially when sulphur is used to control acids in the oil. The notion that, for lube engineers, CI-4 Plus was the most technically challenging standard to date may last a scant two years.