R Synthetics 4 You?

Sometimes yes. Sometimes no.

By John Latta and John Baxter

Synthetic oils: They cost more, right? Well, yes, if you define “cost” as an upfront outlay. But a lifecycle cost analysis, or even a time-specific analysis – winter, for example – might convince you that under the appropriate circumstances, they more than pay for themselves.

Synthetic oil base stocks enable refiners to create engine oils with “better thermal stability,” says Maria Burcham, a technical advisor with ExxonMobil. Thermal stability is critical in keeping oil viscosity high enough for proper component protection.

At the extreme cold or extreme hot ends of the workday temperature scale, synthetics are out-performing mineral oils by losing less of their midrange structure.

“Synthetics offer both superior low-temperature performance and a high level of film strength at high temperatures to better protect all moving parts,” says Dan Arcy, a technical manager at Shell Lubricants. The fluid will be thin enough to flow easily and quickly, and reach all parts when you start up on a cold morning, yet it will remain more than thick enough when running at high speeds on a hot day.

While they are every bit as thick or “viscous” at normal operating temperatures as mineral lube, synthetics will start out thinner when you fire up equipment on a cold morning, says Baxter.

Almost all the oil ends up in the crankcase when the engine sits overnight. When the weather is cold, and at its coldest in the morning when you start work, synthetic oil pumps more quickly and circulates more freely. Also, wear surfaces will be lubricated more quickly with a lower-viscosity oil, and wear will be reduced

“We have a very cold winter now so, for example, there could be benefits to having city trucks with plows run synthetics,” says Arcy. “You get low-temperature pumpability and performance, and also ease and startability. Think what happens if several plows were delayed because they had starting problems, because oil was too thick and it was too cold. That’s costly to the community a number of ways.”

And there are incidental cold-weather costs.

“Cranking a cold engine puts more of a toll on the battery and starter, so there is some advantage there in using an easier-starting synthetic,” says Arcy. “We’ve done testing in cold temps to show how much battery power was needed to start an engine, and it’s significantly less with synthetics.”

The Contamination Problem

In environments where there is a ton of dust getting into the lube, synthetics sometimes lose their edge and may well need to be changed just as often as mineral lubes. It’s the contamination that ruins them and not breakdown. Here we go back to balancing cost and performance.

Any contamination is a threat, and working in a contaminated environment is one circumstance where the use of mineral lubes in drivetrain components might be preferred. In such cases, inspect the lube daily and replace it as frequently as it gets dirty or diluted with a less-expensive mineral oil, says Shell’s Arcy.

“In 2008, Hurricane Ike did some serious damage in Galveston [Texas] and tore up beaches,” recalls Arcy. “They started to rebuild beaches, so they were trucking sand around, working on the shore with dumps that sometimes drove into seawater, with axles going under the water. In a case like that, if I were asked to recommend oils, I wouldn’t have recommended synthetics because that oil would be contaminated, and it doesn’t make sense to use them when they have to be changed constantly in a work environment.”

Research clearly shows that synthetics are ideally suited for use in transmissions and axles, where combustion byproducts are not part of the equation.

Arcy also notes the critical difference between transmission and axle lubes, and the importance of using the right one. Transmission gear teeth are generally flat and the gears sit directly across from one another. In a drive axle, the large running gear sits at the level of the wheel bearings, but the pinion gear that drives it is off-center and at 90 degrees. The gear teeth in the drive axle rub together much more. Your dealer can help your selection for these two distinct uses.