Lube that Lasts
Fortunately, the viscosity scales differ to help set the two lubes apart. Drive axles might use a 75W-90 lube, while a transmission typically uses a 50-weight lubricant.
Synthetic in the engine
The most basic reason for using a synthetic in the engine is its superior performance in extreme cold.
Major refiners offer not only 15W-40 mineral oil, but also 5W-40 synthetic diesel engine oil. “Chevron’s Delo 400 LE Synthetic 5W-40 is a full synthetic product blended with synthetic base oils, and it’s targeted for those customers that want full synthetic protection in extreme climate conditions, specifically cold weather environments,” says Len Badal of Chevron Global Lubricants.
Dan Arcy of Shell Lubricants says a 15W oil flows well down to 5 degrees while a 10W is good down to minus 5 degrees, a 5W down to minus 25 degrees.
In extreme cold, ExxonMobil’s Maria Burcham says synthetics and synthetic blends produce faster starts, saving the batteries and starter, while also providing better protection against engine wear during the first few minutes of operation. Lower viscosity oils result in faster cranking speeds, which not only reduce the amps the starter draws but increase the temperature compression produces in the cylinders, giving quicker firing of the fuel.
After a cold start, almost all the oil ends up in the crankcase when the engine sits overnight. If, under these conditions, the oil pumps more quickly and circulates more freely, the wear surfaces will be lubricated more quickly with a lower viscosity oil, and wear will be reduced. The other justification for using synthetic engine oil is the possibility that it may allow extended changes.
Extending oil changes
Approaches differ among refiners when it comes to adopting synthetics for extending engine oil changes.
Chevron’s Len Badal, when comparing performance of the company’s Delo 400 LE 15W-40 and 10W-30 mineral oils with its synthetic 5W-40, sees a battle of equals. “Both products will provide extended service protection,” he notes, because mineral oils keep getting closer and closer to synthetics in performance due to improving refining. Still, the best synthetics, when specifically designed to provide extended life, are generally considered to have a clear edge.
ExxonMobil’s Maria Burcham says less maintenance and better longevity come with synthetic use. “Better semi-synthetic and full synthetic base oils in conjunction with better additives provide superior protection against corrosive and abrasive wear,” she says.
Shell’s Arcy agrees on the oil durability issue, saying full synthetics “have better oxidation stability.” This means they will survive longer without losing their viscosity or becoming acidic.
Even with super oils, Arcy says “optimizing” drains should be the focus more than extending drains because it is impossible to accurately predict well in advance the correct times to change. One thing that affects the drain time is maintenance of the cooling system, air induction system and other basic systems that can impact the rate at which oil deteriorates.
Finally, since oil gets contaminated even in properly maintained engines, a careful program of oil analysis is essential to help determine what factor is limiting the life of the oil, and whether or not the lubricant choice will help the problem. Arcy says, “If the condemning factor is fuel dilution, a synthetic might help, but if it’s high soot, it won’t change the interval much.” n
The synthetic oil payback
Even though it often costs twice as much as standard mineral oil, synthetic oil can be a more effective engine oil choice when other factors are considered.
This example is based on a truck traveling 120,000 miles/year moving from 15,000-mile changes to 40,000 miles, and moving from a $17 per gallon mineral oil to a $34 per gallon synthetic. Filters are changed once per change with mineral oil, and twice per change (once midway in the change cycle) with synthetic.