Mankind has known something about lubrication ever since the invention of the wheel, which was at least 6,000 years ago. But back then animal fat on a wooden axle was about as far as it went. Today, of course, lubricants have gone hightech, motor oil in particular.

Oil has more to do than just provide an unbroken film of slick molecules to keep metal-to-metal contact from occurring inside an engine. It also has to seal the rings against their lands and the cylinder walls, keep dirt in suspension, battle crankcase chemicals that form sludge and varnish and promote corrosion, absorb shocks, and act as a heat exchange medium.

No matter how carefully refined the base stock, straight mineral lube is totally inadequate for these responsibilities, so modern oils contain a blend of fortifying additives. These include:

• Detergent dispersants to pick up dirt and keep it from collecting in lumps.
• Viscosity improvers to reduce the rate of thickness change from one temperature to another.
• Extreme pressure agents to increase film strength and keep the oil from being squeezed out of load-bearing joints.
• Pour-point depressants to make the lube more enthusiastic about flowing out of a can or into a bearing at low temperatures.
• Defoamants to control frothing.
• Antioxidants to help prevent overheated and churned-up oil from thickening and forming tar and varnish.
• Friction modifiers to cut internal drag.

Categorizing quality

Way back in 1911, SAE started to classify motor oil by viscosity, but it wasn’t until 1947 that quality was taken into account with three API (American Petroleum Institute) grades: Regular, Premium, and Heavy Duty. Five years later, the original ESCS (Engine Service Classification System) was established, which amounted to a more comprehensive description of what was needed for different service situations.

Since 1970, API has used basically the same oil classification system we have today, which it worked out with both SAE (Society of Automotive Engineers) and ASTM (American Society for Testing and Materials). Under the “S” (Service) heading, grades range from SA (almost pure mineral oil totally obsolete because it’s not useful for much more than softening skin) to SG (the good stuff). Under “C” (Commercial, which means diesel) there’s CA (also obsolete) to CE (for severe beating with turbo or supercharging). The best oils available now meet both SG and CE, so you won’t have to stock something different for diesels.

Viscosity resistance to flow is classified by SAE. There are two types of ratings, one for winter (SAE 5W, 10W, and 20W), and another for the rest of the seasons (SAE 20, 30, 40, and 50). The winter grades are tested at 0 deg. F., and the others at 210 deg. F.

Multi-viscosity oils have what’s known as a high viscosity index, which means that their fluidity and body change relatively little from one extreme of temperature to the other. For instance, 10W40 meets the SAE 10W standard at 0 deg. F, and the SAE 40 standard at 210 deg. F., so it flows well enough to provide a supply of lube to the bearings and allow easy starting at low temperatures, yet doesn’t thin out very much when the engine gets hot.

The space at the bottom of the API “donut” symbol is reserved for the oil’s fuel saving rating. If it just says “Energy Conserving,” it cuts friction enough to increase mpg 1.5% over a standard test reference oil. But the latest level is “Energy Conserving II,” which can mean up to a 3% improvement. In a car with an average EPA rating of 25, that translates into .75 mpg, which is worthwhile if not dramatic.

Manmade

The history of synthetic oils is longer than you might think. Development began in the thirties, and both the Allies and the Axis used them in WWII. They kept German tanks rolling on the frigid Russian front, which may not be an accomplishment to brag about, but science knows no politics. With the advent of the turbojet engine, ordinary oil’s tendency to boil away became painfully apparent, so synthetics found an important niche in the aircraft industry.

In spite of having been around for half a century, the market penetration of synthetic oil is still very low because it costs maybe four times as much as you’re used to paying for a quart of slippery stuff, so companies that want to sell it have to prove that it’s better a lot better.

But in most ways, synthetic oil IS a lot better. Chemists “build” PAO (polyalphaolefin) and ester base stocks with properties that are predictable and stable.

A chemist with a major lubricating oil company described it this way: “Synthetic base oils are produced from either crude oil or natural gas, where ethylene is produced. The ethylene is then passed through catalysts and hydrogen to form the chemical structures that make synthetic base oils. Natural petroleum base oils, on the other hand, are manufactured by refinery distillations, solvent extraction, and dewaxing. The additives used to formulate natural engine oils are the same as those used in synthetics.”

One of the qualities of this manmade lubricant is an amazing resistance to viscosity change. Oil thickens with use because its lighter, more volatile fractions boil off leaving the heavy stuff behind. But some synthetic formulations exhibit only one tenth the thickening of conventional oil. This low volatility can also cut consumption because most of the lube an engine in good condition uses is lost as it flashes into vapor at the rings.

Then there’s the opposite end of the scale: cold weather performance. Again, the difference is impressive. At 50 below, a good synthetic is still fluid, whereas regular oil, even with a first class pour point depressant, has the consistency of peanut butter.

The chemist quoted above told me, “Synthetics have better oil film thickness and a higher viscosity index. They’re much more fluid, so they run cooler. On the Corvette LT1 engine, they were able to eliminate the oil cooler by specifying synthetic oil.

“Actually, on both the LT1 and the GMC Syclone, you won’t find the word ‘synthetic’ anywhere in the service requirements. It’s just that nothing else can meet the specifications given.”

There are a few cautions to observe with synthetics. According to the same chemist, “On pre1980 cars, you may have seal problems (newer cars have compatible seals). And if you have an oil leak or oil consumption problem on any year car, you’ll definitely find out that you’ve got it because synthetics flow more easily through bad seals or worn rings.” Also, since its lubricating characteristics are so good, it’s not the right stuff to use for engine break-in some wear is necessary to seat all those nice new parts.

Read Part Two