Motor oil is a product that has changed quite a bit in recent years. With longer and longer intervals between oil changes, the quality of motor oils has gotten better and better with higher-grade base stocks with partial or full synthetic formulations. Synthetic oils are often recommended or required for extended oil drain intervals.
The increased emphasis on fuel economy also means today’s oils are thinner and contain more friction modifiers and viscosity extender additives. Most late-model vehicles are now factory-filled with 5W-20 or 5W-30 multi-viscosity oil, and some are even using oils as thin as 0W-20. Thinner oils are usually required for overhead cam engines to speed upper valvetrain lubrication following a cold start. For older pushrod engines, 10W-30 is still a popular viscosity. The best advice here is to follow the viscosity recommendations of the vehicle manufacturer.
Another change that has taken place in motor oils in recent years has been a drastic reduction in the amount of zinc and phosphorus (ZDDP) anti-wear additive in the oil. ZDDP can contaminate and shorten the life of the catalytic converter and oxygen sensors, especially if the engine burns oil as it ages. Most late-model engines do not require much ZDDP because they have low-friction roller cams or overhead cams with followers. However, older vehicles that have pushrods engines and flat tappet cams still require higher levels of ZDDP to prevent cam wear and failure. Since modern oils don’t contain the same amount of ZDDP they once did, a ZDDP supplement additive is recommended to protect the cam and lifters.
Some oils are also specially formulated for older high-mileage (75,000 miles or more) engines. Such oils typically contain extra additives to counter the effects of leaks, deposits, sludge and friction. Seal conditioners help keep crank seals soft and pliable so they don’t leak. Detergents and dispersants help keep the engine clean.
Another change in motor oils is the introduction of more “green” products that contain up to 50 percent ore more “re-refined” motor oil. The used motor oil in these products has been recovered and fully reprocessed using a multi-step refining procedure that is similar to that which is used to refine crude oil. The resulting base stock is as good or better than a comparable traditional base stock, and meets the same API and OEM performance requirements when it is reformulated with the proper additives. Re-refined motor oil is being used successfully by numerous fleets, the U.S. military and ordinary motorists.
The greatest benefit of re-refined motor oil is that it recycles a valuable product that might otherwise be burned or discarded. The U.S generates more than 1.4 billion gallons of waste oil annually. Re-refining used motor oil uses 85 percent less energy than refining crude oil, and allows used motor oil to be recycled as many as eight to 10 times!