[Skip to Content]

A closer look at synthetic motor oils

By on January 1, 2016

For years the only decision a truck driver needing oil for a diesel engine had to make was which brand of 15W40 to purchase. But the trucking industry has slowly and surely been making the adjustment to synthetic oil. Now, 10W30 is an option and there’s even talk about 5W30. How did this happen? Engine manufacturers are under the gun from the EPA to improve fuel economy and friction is eating into their efforts. The solution is a move to lower-viscosity oils in newer engines.

But having more choices can be confusing, and even overwhelming, because when you put oil in a vehicle you are affecting the way an engine that costs $30,000 to $60,000 works. Understanding the nature of lubricants and how they work can help drivers make an informed choice for their particular vehicle and the way they use it.

Cracking the code

The numbers on the oil container tell you about its viscosity — the speed of flow. The first set of numbers followed by the “W” designates the viscosity of the oil when it is cold. The second set of numbers signifies the viscosity when the oil is at operation temperature. A higher viscosity means that the oil is thicker and flows more slowly. Lower viscosity means that it flows more easily, and higher resistance to temperature means that it does so even when the engine is cold.

What is a synthetic oil?

The mineral oils used in cars and trucks for the last 100 years are derived from crude oil. Because they developed naturally, in the ground, they are made up of molecules that vary in size. Yes, the oil goes through a refining process, but that does not affect its molecular structure.

Synthetic oil is manmade to have uniformly sized molecules. It uses polyalphaolefins (POA), a class of polymers made from chemically modified petroleum products like methane, carbon monoxide and carbon dioxide. Synthetic oils are “polymerized” in a way that allows the manufacturer to customize for particular performance properties.

Main advantages of synthetics

First and foremost, the uniformity of the synthetic oil molecules mean that it creates less friction as it flows through the vehicle. It is slicker than conventional oil and so picks up fewer contaminants as it does its job of lubrication. Less friction means the motor works more efficiently and that means greater fuel economy.

Oxidation stability is also greater in synthetics, which means it is less likely that oxygen will mix with the oil and break it down, so the engine stays cleaner. Lower volatility means there is less evaporation. Anyone who has ever owned an old clunker of a car and always kept a case of oil on hand to keep going between oil changes understands just how important that is. The oil lasts longer in the engine. Less oil burning, as well as better fuel economy, contributes to lower emissions, too. The lower pour-point — the lowest temperature at which the oil can still be poured out of a container — helps the engine start faster and reduces engine wear on cold starts.

There are many drivers who will be happy to argue the benefits of conventional oil over synthetic oil. But one fact that is undisputed is that lower viscosity and higher resistance to temperatures, the main properties in synthetic oils, result in 2 percent or better improvement in fuel economy and reduced wear in the engine So, lower viscosity synthetics may be worth a second look. But always be sure to consult the engine manufacturer’s oil requirements for your specific engine.

Homer Hogg’s “Maintenance Matters” airs on the Dave Nemo Show (Road Dog Trucking, SiriusXM 146), 8 a.m. ET, the first and third Thursday of each month.

About Road King

For the professional Driver

Leave a Reply

Your email address will not be published. Required fields are marked *