Motor Oil Myths

Everything You Need To Know About This Slippery Subject

By Evan J. Smith

Photography by Courtesy of the Manufacturers

Of all the inventions man has created, few rival the Internal Combustion (IC) engine. This amazing machine does the work of many men by producing horsepower and torque, and does so in a short time and generally with great efficiency. In the last 100 years there have been many improvements in power, emissions, and reliability to the IC engine.

Racers and enthusiasts continually take these engines to the edge by extracting greater horsepower and torque as compared to stock units. We enhance output with aftermarket parts and trick tuning, but rarely do we pay much attention to such things as the oiling system--at least until the engine burns up.With that said, we urge you to get educated. Lubrication is necessary, and picking the right kind is important to longevity and performance. Thankfully, it really isn't that hard if you know the facts. Without them, though, even the most carefully prepared engines may lock up and die.

Engine Oil
We know that oil lubricates the engine, but it also cleans it and provides a means for cooling by dissipating heat. Oil also suspends minute particles of foreign matter so they don't become imbedded in critical components such as the bearings and/or the oil pump. In addition, oil must work in a harsh environment, getting whipped by the crank, dragged by piston rings, and forced through small clearances.

A quality product is important, but what's the difference between that dusty $1.29-per-quart oil found at the supermarket and the specially designed racing oils that sell for more than $10 per quart? And what's the difference between mineral oils, synthetic oils, and blended oils?

Frankly, there are enough grades and types of oil to make your head spin. Nevertheless, at the end of the day, most people just want to know what's the best oil for their application.

The lubricant we know as "engine oil" comes in many grades and blends. Regardless of the type, all oil begins life as crude oil. Crude oil can be many colors, but most of us know it as the thick, black stuff that comes from the ground.

Crude oil is a versatile product containing many hydrocarbons--molecules containing hydrogen and carbon. Hydrocarbons have the potential to release a lot of energy, but they must be refined before they can be used efficiently.Refining is a process that separates the chains of hydrocarbons within the oil. Once the oil is refined, many useful substances can be created, including gasoline, diesel fuel, kerosene, petroleum gas (used for heating and cooking), along with heavy oils and lubricating oil.

"Crude oil is refined to make base stocks," says Mark Ferner of Quaker State. "Base stock makes up about 80-85 percent of a quart of oil. The remaining percentage is made up of about a dozen additives that enhance certain properties. These may include anti-wear, detergent, dispersants (which hold debris in a suspended state), foam inhibitors, friction modifiers, and a few others."

Mineral-based oils are the most common, but there are also synthetics and blended oil containing a mineral/synthetic mix.

Synthetics are known as man-made oils, but they are not created totally from scratch. "Synthetic oils are created from crude, but the refining process is much different than with mineral-based oils," says Jared Martin of Royal Purple. Synthetics are first broken down or refined well beyond that of mineral oils, and then they are practically recon-structed so the chains or molecules are uniform. This additional refining also drives up the cost of synthetics.Synthetic oils offer superior high-temperature oxidation resistance, higher film strength, a stable viscosity base, and better low-temperature flow characteristics. This makes them a good choice, as long as you can afford the extra cost.

In addition to mineral oils and synthetics, there are also blended oils, which are made up of a combination of mineral and synthetics. Blends allow manufacturers to build customized oils to fit the cost, compromise, and performance that customers desire.

Lubrication
On the most basic front, the job of the engine oil is to lubricate moving parts inside the engine. Where there are moving parts, there will be friction, and friction takes power to overcome. Excess friction leads to metal-to-metal contact between internal moving engine parts. Without lubrication the parts would grind together and the engine would seize. On the other hand, reduced friction means more power and greater overall efficiency. It also reduces wear and increases engine life.

The oiling system is relied upon to get oil to the critical parts of the engine. Most oil systems are made up of an oil pan, an oil pump, a pump pickup, an oil filter, oil passages, and a return system. Oil is picked up and fed to the pump and then the filter. Oil is then routed to the passages in the block and to the clearance areas between the bearings and the crank. Oil then flows through passages in the crank, which feeds the rod bearings. Excess oil is thrown from the crank and it splashes on the cylinder walls to lubricate piston and ring assemblies.

Passages in the block also feed the cam and the lifters. The lifters feed the pushrods, which feed the top end of the engine. Through passages in the heads and block, oil drains back to the pan and the cycle starts over.

This type of system is called a wet-sump system. Dry-sump systems, used primarily in racing, use a remote reservoir and an externally mounted pump. The pump supplies oil to the engine through lines. This pump also scavenges the pan of any oil and feeds it back to the reservoir. Horsepower can generally be found with a dry-sump system because the crankshaft never contacts the pool of oil, and windage is greatly reduced.

Viscosity
One of the most commonly used terms found in conjunction with oil is viscosity. Viscosity is simply the oil's resistance to flow, but we commonly think of it as the oil's thickness.

"The Society of Automotive Engineers (SAE) sets the parameters for which lubricant viscosities are determined," says Martin. "Viscosity is defined as the resistance to flow at a given temperature. But, without a corresponding temperature, a viscosity measurement is meaningless. There are two ways of measuring viscosity: Saybolt Universal Seconds (SUS) and Centistokes (cSt). Each lubricant is measured at two temperatures to determine the SAE viscosity simulating ambient temperature flow and operating temperature flow. When measuring in centistokes, the lubricant's flow is measured at 40 C and 100 C. When measuring in SUS, the fluid is measured at 100 F and 212 F."

In lay terms, thin oil receives a low viscosity number, such as SAE20, and thicker oil receives a higher number, such as SAE40. It's important to remember that the SAE number is arbitrary because it labels the oil's viscosity at one given temperature, and that viscosity can change with temperature.