Oil technology has produced a wide range of varying-viscosity, multigrade oils that are extremely reliable. Recent revisions to cold-flow requirements ensure that cold oil is thin enough to circulate quickly through a cold engine for start-and-drive-type drivers. Protection, however, is only one area of concern from auto manufacturers. Oil's effect on fuel economy is the other.
It is formulated to reduce friction without compromising protection. Since lower-viscous oils generate less oil-pump drag than higher-viscous oils, lower-viscous oils typically utilize less power to circulate. The ideal multigrade oil is one that circulates with the least amount of drag, yet is heavy enough to sufficiently protect in normal conditions. This creates slightly better engine efficiency, which can translate into a marginal fuel economy increase. This compromise is why auto manufacturers commonly use 5W-20 and 5W-30 oil in today's engines.
The drawback to low-viscosity, multigrade oil is that it can offer less high-temperature protection. This does not suggest, however, that higher-viscous oils will offer any better protection in extreme conditions. Any oil can become dangerously thin, offering little to no protection if oil temperature grossly exceeds its intended operating range. But since most passenger cars are driven mild-to-moderately in all types of climates, 5W-20 to 10W-30 oils typically suffice.
Major Analysis Organizations
There are two major organizations that rate oil quality for maximum consumer and environmental protection. One is the American Petroleum Institute (API); the other is the International Lubricant Standardiza-tion and Approval Com-mittee (ILSAC). Either is recognized by--or assembled of--representatives from the federal government, major auto manufacturers, or major oil companies. These organizations set the oil-quality standards and then issue approval ratings based on performance testing.
API ratings consist of a two-letter system that begins with either an "S" or a "C." S-rated oils are approved for service-class engines, or gasoline-powered engines used in cars and light-duty trucks. C-rated oils are approved for the demands of commercial-class vehicles such as heavy-duty, diesel engines. The letter following either is an oil approval rating. Latest API ratings include SM and CI for the respective categories.
ILSAC approval is similar to that of API. Its rating system, however, consists of a "GF" followed by a number. GF stands for "gasoline-fueled," and the number following is ILSAC's quality rating. The latest ILSAC standard is GF-4.
As oil quality increases to meet new emission and performance standards, API and ILSAC designate a sequentially higher letter or number to each new category, which oftentimes supersedes its predecessor. We must realize, though, that any current oil can be approved for a past category, but it cannot be approved for the latest until it meets or exceeds that expectation. The category rating of any oil is typically posted on the container label.
Recent Oil Formulation Changes
Auto manufacturers have been required by federal law to warrant specific components of the emissions control system on any '95-or-newer car or light-duty truck for the balance of eight years or 80,000 miles--including catalytic converters. In that time, it has been determined that phosphorus in exhaust can negatively react with the converter's active catalysts, rendering it inoperable. The cost of component replacement cannot only fall upon the manufacturer, its failure can also create a vehicle that excessively emits pollutants until said repair is made.
The largest amount of phosphorus inside an engine is in its oil. A compound molecule named Zinc Dialkyl Dithiophosphate (ZDDP) is comprised mostly of zinc and phosphorus, and has long been a common antiwear oil additive. ZDDP offers key frictional-heat-activated qualities that form a sacrificial chemical barrier on components that are under continuous high-pressure contact. While much of the oil would literally be squeezed from between the components in these conditions, ZDDP prevents the metal-on-metal contact that could otherwise result. A classic example would be a camshaft lobe and lifter.
Since phosphorus has been proven to negatively affect catalytic converters, auto manufacturers and oil companies are working to find a suitable antiwear additive to replace ZDDP. But that has been a major task. So, until it happens, the analysis organizations have imposed a temporary limit on the maximum amount of ZDDP in oil--no more than 0.01 percent by weight. It appears this reduction has had a major effect on the hobby since its enactment in January 2004.