Determining the right oil for your vehicle, combined with regular preventative maintenance, can improve engine performance and longevity, resulting in lower lifecycle costs.

There are two things that could damage an engine: excessive heat or lack of lubrication. This is truer today because while modern engines are designed to burn cleaner, they also run hotter.

So how do you decide what's the best oil for your vehicles?

A good starting point would be the Institute of Materials (IOM), an independent organization that conducts research on oil samples from around the world, then provides the results to automakers, oil companies, and fleet managers. These results are called VoxPopTM reports.


Weather Plays a Key Role When Selecting the Proper Oil

Vehicles run by MediaOne, in Lawrence, MA, use 10W-30 primarily because of its good start up and flow characteristics in cold weather, said Jeri Buckley, MediaOne's fleet manager. Many of the company vehicles, of which a majority is vans, remain idle frequently, she said.

"It can get pretty cold where we are, the Northeast region," Buckley said. "We didn't want to use oil that's too thin, like the 5W-30, because of the vehicles being idle. The 10W-40 is probably a bit too thick, and we wouldn't want any start-up problems in the morning."

But the case is different in Harris County, TX, where the climate is a lot warmer. Since most of the county vehicles, they use higher-viscosity oil, such as 20W-50, said Keith Bramer, director of vehicle maintenance for Harris County.

Understanding the Different Oil Classifications

Determining the best oil depends primarily on what you need. Some oils pump well in cold weather; others at high temperatures; and others burn off a high percentage at running temperature.

But there are other considerations. IOM has provided basic terms to give people a better understanding of the nature of the oil and how classification is established. They include the following:

Viscosity. This is the single, most important property of an oil. Viscosity is how fast an oil flows. The viscosity of an oil must be thick enough to lubricate and protect, but thin enough to flow through oil lines and spread evenly over all bearing surfaces at low temperatures.

Oil Grade. The oil grade is the measurement of how fast it flows or its viscosity. The Society of Automotive Engineers (SAE) has established a rating system to indicate an oil's viscosity or thickness and assign it a specific grade number. Thicker oil flows slower and is designated a higher SAE number.

Multigrade Oils. These oils have two SAE grades - for low and high temperature characteristics. The first SAE number, such as "5W" (W stands for winter), indicates oil flow characteristics at cold start, while the second number, such as 20 or 30, refers to film strength at 212 degrees Fahrenheit.

In cold weather, it would be best to use a multigrade oil with good start-up and flow behavior, such as a 5W-30. But an older engine, or one that operates at high temperatures, a higher viscosity oil, such as a multigrade 10W-30, would be preferable.

Mineral Oils. Originating from petroleum deposits in the ground, these oils vary greatly in quality, sulfur content, how cleanly they burn, and the amount of carbonized deposits they leave on internal engine parts.

Synthetic Oils. Synthetics tend to have lubricating qualities resistant to high-temperature breakdown and deposit formation. But they require additives due to lack of natural lubricating properties. In general, synthetic oils are best used in turbocharged/high-performance engines with tight tolerances and high operating temperatures.

Service Classification. Set by the American Petroleum Institute (API), the classification appears as letters in the doughnut-shaped ring on oil containers. The system rates an oil's ability to control wear, sludge, varnish, thickening, rust, corrosion, and piston deposits. The latest classification is SJ, but letters changes as standards are continually upgraded. The SJ rating will also carry the International Lubricant Standardization and Approval Committee's (ILSAC) symbol, meaning that it meets standards set by American and Japanese automakers.


What the Terms Mean

VoxPop reports provided by the Institute of Materials have eight rating categories that measure the qualities of oil and how those qualities change during engine operation.

Starting Viscosity - How easily the oil flow will let your engine start at cold temperatures. Lower numerical values are better.

Pumping Viscosity - How easily oil flows from the oil pump in cold temperatures. Lower values are better.

Gellation Index - An oil's tendency to form gelled structures in the oil at cold temperatures, making flow to the oil pump more difficult. Lower values are better.

Operating Viscosity - The ability of an oil to lubricate critical areas of the engine, such as bearings and cylinder walls where temperatures can exceed 250 degrees Fahrenheit during normal operation. Higher numerical values are better.

Oxidation Resistance - Oxidation leads to the formation of acid and deposits within the engine and may increase oil viscosity. Under harsh test conditions, resistance to this chemical change is measured in minutes until oxidation occurs. More minutes of resistance are better.

Volatility - The percentage of oil lost through evaporation or burn-off during engine operation. Lower percentages are better.

Shear Stability - The percentage of viscosity lost during engine operation. This is a measure of how well an oil retains its viscosity when used in the engine. Lower percentages are better.

Acid Resistance - The ability of the oil to neutralize harmful acids, formed in the process of fuel combustion and oil oxidation. Higher values are better.