By Jim Fitch
Machinery Lubrication Magazine
Industry rides on a film of oil. The oil’s viscosity bears the load and defines the extent of clearance achieved between working surfaces. Sometimes that clearance is thick and bountiful, and other times it is deflated or extinct. Without viscosity, most machines would rapidly self-destruct with mechanical friction and wear.
There is also a well-known penalty and reliability risk from too much viscosity. Like most things, the selection of a lubricant’s viscosity must be optimized to enable needed protection and disable the danger from excessive viscosity. For instance, too much viscosity can cause churning losses and excessive heat generation from molecular friction. It can also impede lubricant movement and flow to lubricant-hungry surfaces.
One of the most famous disadvantages of too much viscosity is high energy consumption. In recent years, we’ve seen automaker-specified viscosity being lowered in crankcase service from 5W40 to 5W30, and now in some cases to 5W20. These changes are all for the sake of energy conservation.
Of course, the primary driver for energy conservation is not to save money on fuel or electricity but rather to reduce the consumption of fossil fuels, which emit harmful gases (carbon dioxide, nitric oxides, hydrocarbons, etc.) into the atmosphere as a byproduct of combustion.