Mr. Green Car: Oil philosophy 102—synthetic oil

Engine_AP-WBy Allen Penticoff

Free-lance Writer

I’ve had little firsthand experience with synthetic oils. Primarily with what lubricates turbine aircraft engines, and, to a limited extent, some semi-synthetic oil used for a while in a Chevy Suburban. So, I had to do a little research to find out what, precisely, synthetic oil was before passing judgment on it.

First, research in the 1930s and 1940s by Dr. Hermann Zorn of I.G. Farben Industrie in Germany and separately, by Dr. W.A. Zisman working for the U.S. Naval Research Laboratory, both investigated esters, diesters and polyol esters as replacements for natural “mineral” oil (the stuff they pump out of the ground). These non-mineral oils were sought to have the lubricating properties of natural oil, but without their tendency to have gum deposits or gelling. World War II found the first synthetic oils being used in aircraft engines. In Germany, this was because of limited oil resources and cold weather issues, while the U.S. forces were relying on this new oil to aid in cold starting and reduced soot deposits.

Basically, there are two kinds of synthetic oils—those from Polyalphaolefins (PAO) and those that are ester- or diester-based. In the mid-1960s, Chevron introduced synthetic oil to the consumer market with PAO-based oils. In the early 1970s, other companies: All-Proof, now Red Line and Hatco sold by marketer Amsoil, were diesters or poly esters, while Mobil 1, a PAO, came along in 1974.

The American Petroleum Institute (API) classifies PAO oils as “Group IV” base oil, while non-PAO synthetics are part of the very broad “Group V.” There is a Group III that is in a fuzzy land, being called a synthetic (U.S. only), but is derived from mineral oil vapor. This is important to you only in comparing oils and their relative performance.

I’ve still yet to find out what “non-natural oil” this stuff is made of (bananas?). Some newer oils are biodegradable, and there are experiments under way in making oil from plastic bottles. Wherever it comes from, their chemicals are blended in a way to tailor them to have predictable properties via a controlled molecular structure. Simply, they can make the same thing over and over identically, while natural mineral oil is constantly varying somewhat in its richly complex structure that includes compounds that are somewhat detrimental to the mission of a lubricant.

To some extent, most motor oils have some synthetic in them, as our modern multi-viscosity oils depend on polymers (plastic) to thicken oil as it gets hotter. They start with a thin base mineral oil, say 10 weight (W), and let the polymers expand/thicken as it warms until it is acting like it is 40 weight. This allows the engine to spin easily at a cold start, yet still keep the metal parts from contacting one another later when they warm up, which is the whole purpose of oil.

In general, pure synthetic oil is slipperier than mineral oil, reducing friction—particularly at cold starts. In older cars before machining was more precise, one had to break an engine in on mineral oil since the engine actually needed some wear to polish the components—so starting out with a synthetic was not recommended. On the other hand, many new cars hit the showroom floor with synthetic oil in them. Mobil 1’s Web site claims no “engine flush” is needed to switch to their synthetic oil; however, such a flush may not be a bad idea if one is changing lubricants, particularly in a more experienced engine.

It takes energy to pump oil around inside an engine, and the thicker the oil, the more energy it takes. To increase fuel economy, newer vehicles have recommended oil viscosities as low as 0W-20. That’s pretty thin oil. Using synthetic’s slipperiness allows such thin oils and tighter part clearances. The big problem with synthetic oil is cost. Starting at about $5 per quart and heading up from there, synthetic oil is significantly more costly than mineral oil; and the performance and longevity gains may be difficult to justify the additional expense.

Consumer Reports did some testing in taxicabs in 1996 and found the stop-and-start use of taxicabs did not show any appreciable advantage in synthetic oils. Critics of that report claim cab driving is not where synthetics shine, which is with very cold starts and under loads with high heat.

Synthetic oils typically call for long intervals between oil changes. A possible downside to extended oil change intervals is that you don’t get the combustion byproducts (condensation acids, et. al.) out of the engine soon enough to prevent damage, yet the synthetic oils seem to provide adequate protection during long oil change durations. They also help prevent wear on that first second your engine is turning over before the start and oil starts pumping through its veins.

So, synthetic seems as if a trade-off of potential benefit versus cost. Fewer oil changes are claimed to be better for the environment, but in reality, the used oil, as long as it is properly disposed of, is usually recycled or used in some fashion, and, therefore, is not much of an environmental factor. The biggest environmental gain of using synthetic oil is increased fuel economy, so most vehicle manufacturers are heading in that direction to gain any efficiency they can to promote their product as being thrifty with fuel.

I find synthetic oil users are like religious converts—they all believe strongly in their choice—so finding an unbiased opinion is hard to come by. I hope I’ve been one here.

From the September 9-15, 2009 issue

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