The simple answer to the question posed above comes when the manufacturers of your equipment recommend the use of synthetic oil for their machines. “This is the manufacturer telling you that for peak performance and longevity, the extra cost of using a synthetic lubrication is justified,” explains Stede Granger of Shell Lubricants. “This is not to say that synthetics are always better in every application than mineral-base lubricants. They both have their place.”
Differences in oil base
To determine when synthetics provide an economic advantage, you need to understand how they are manufactured. Take heavy-duty diesel engine oils as an example.
Oils derived from a mineral base (commonly petroleum crude oil) comprise approximately 75% to 85% base oil; the remainder of the fluid is made of additives. These additives are chemical compounds used to enhance or to impart new properties to the base mineral oil. For example, zinc dithiophosphate is added to engine oils as an antiwear agent to minimize metal wear. Also, magnesium is added to remove soot, carbon, or unburned fuel.
Synthetic oils are created by chemical synthesis rather than by conventional refining. This synthesis involves the polymerization of hydrocarbons (olefins). The three most common types of synthetic base oils are polyalphaolefins, organic esters, and polyglycols. Of these three types, polyalphaolefins are the most common and moderately priced synthetic-base oils in use today.
Now, it is the chemical process used to create synthetics that provides the lubricants' chemical uniformity. Thus, a synthetic oil's molecules are very uniform, whereas, mineral-base molecules can vary widely. This is the synthetics' major advantage over mineral-base oils.
Uniformity combined with additive packages creates an oil that has myriad attributes, which include:
● High-temperature stability that results in reduced oil consumption.
● Low-temperature fluidity (flow), which means easier starting at low temperatures.
● Longer drain intervals.
● Higher viscosity index.
● Less oxidation, which provides for longer drain intervals and longer filter life. (Oxidation of the oil creates particles that deposit on filters.)
● Reduced fuel consumption (up to 5%) in some applications.
These performance advances have come in response to manufacturers pushing the performance of mechanical components on their machines. But the benefits of synthetics come at a price.
One example of how that high cost pays off is found in engines that operate for long periods of time at the same speed in hot conditions, like those operating irrigation pumps. “These are harsh conditions when engine and oil temps ride high,” says Mark Betner of CITGO. “A synthetic oil is far less apt to break down in this operational situation and will actually help reduce oil operating temperatures.”