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Slick guide to grease
Grease is often the poor stepchild of a farm's lubricant family. Liquid lubricants – like engine and transmission oils – get housed in modern amenities such as vented poly-stacked tanks. Tubes of grease find their way to the backs of pickup beds or tractor toolboxes, exposed to summer heat and severe winter cold. Yet they are expected to flow like warm butter through any grease gun and protect bearings even years after the grease was purchased.
Grease is the most forgiving of all lubricants used in agriculture, says Matthew Sivik of Lubrizol Corporation. “But it has a service limit,” he says. “Also, if the right grease is not being used in equipment, you could be paying too much for replacement parts. On the other hand, the right grease can allow equipment to run for years without a maintenance problem.”
Making matters worse, grease suffers from a number of misunderstandings, like the fact that its thickness makes it lubricate better. Grease is basically oil suspended in a thickener that holds the lubricant between its lattice-like fibers, explains Mark Betner of Citgo. As temperatures increase during use, oil bleeds from the grease.
Conventional vs. synthetic greases
Conventional greases, most common in farm use, employ a mineral oil suspended in such thickeners as lithium (the most common) or calcium. But the market does offer synthetic greases, which employ a lubricant such as silicone, for example.
Each grease has its advantages. Conventional greases are the cheapest to buy. Synthetics, however, are finding ready use in automotives, since they perform well at low-temperature, low-torque applications such as in wheel bearings running in the winter.
Greases also get formulated with additives that protect metal parts from corrosion and rust, and enhance their durability. A common additive in grease formulated for farm equipment is molybdenum disulfide (moly grease) that provides “plating protection even if the grease gets pushed or washed out of a bearing,” Betner says. “It stays in place even though the thickener has left.”
Grease has grades
Grease is also graded by its thickness and fluidity. Essentially, the difference between grades boils down to how much thickener is added to the base oil. The higher the grade number, the greater the amount of soap is used and the greater the tendency for the grease to stay put in heavily loaded components.
The most fluid grease (you can even get grease that is solid as soap) is rated Grade 000; it has the consistency of molasses. Grade 2 grease (thicker than Grade 000) is the typical year-round grease found on most farms, providing a balance between pumpability and clingability, both attributes described by the National Lubricating Grease Institute.
Any Lubricant Has a Limited Shelf Life
In general, liquid lubricants will remain intact for several years. But over time, grease can thicken and age-harden if stored too long. The oil and its thickener can also separate with time. Think, for example, of the oily exterior on a tube of grease. “Slight separation (of oil and its thickener) is common and harmless,” says Walt Silveira of Shell Lubricants.
The general rule for all lubricants – liquid or grease – is that the simpler the oil formulation, the longer its shelf life. For example, engine and transmission oils have a suggested shelf life of three years, while metalworking and cutting oils only have a one-year shelf life. Signs of storage instability include the settling of additives as a gel or sticky liquid, a haze, hardening, and color changes.