Grease vs. Oil: Which Is the Best Lubrication Method?

According to some engineers, lubricants are simple byproducts of the former Industrial Age. The lubrication of machine bearings is a long-standing practice that has seen various advancements over time such as the tweaking of chemicals, leading to modern day solutions that are commonly used to minimize friction. Still, the introduction of oil-based lubricants in the late nineteenth century accelerated today's modern lubrication methods.

Engine oil (mineral oil) and automotive grease are two distinct automotive lubricants used to keep an engine's parts well-lubricated. Both lubricating grease and oil share common ingredients, such as additives and base oils.

However, the primary difference between the two is that grease uses a thickening agent as its constituent, apart from the base oil already in use, impacting its viscosity and consistency. The thickener converts the grease into a viscous oil, enhancing its adhesive properties. To better understand the differences between grease and oil, let us further dive into how they can be applied to see which is better for your unique needs.

What Are Grease-Based Lubricants?

Greases are created by combining oil (most commonly, mineral oil) with thickeners (for instance, lithium-based soaps). They may also contain lubricating agents such as molybdenum disulfide, graphite, or polytetrafluoroethylene (PTFE or Teflon). Greases combine the lubricating nature of oils with their inherent adhesiveness, allowing for the effective sticking of the lubricant to surfaces.

Grease-based lubricants can even be designed to act as a barrier, keeping contaminants from damaging or corroding surfaces. Like oils, greases are available in many thickness ranges, from viscous to free-flowing. Moreover, the overall stickiness and thickness provided by a grease can cause resistance in fast-moving or small mechanisms.

What Are Oil-Based Lubricants?

Oil-based lubricants are most commonly used in high-temperature, high-speed applications where the deflection of heat transfer away from in-operation bearing surfaces is required. Bearing oils are natural mineral oils mixed with oxidation and rust inhibitors or synthetic oils. The base products in synthetic oils are typically polyalphaolefins (PAO), polyalkylene glycols (PAG), and esters.

Mineral and synthetic oils have distinct properties and should not be used interchangeably despite their similarities. One of the most important factors to consider when choosing an oil for a bearing is its viscosity. The viscosity of a fluid is the measure of its internal friction or resistance to flow. While high viscosity fluids are thicker and lack flow, low viscosity fluids are thinner and move more freely. When calculating a fluid’s resistance, it is measured in Saybolt Universal Seconds (SUS) and centistokes (mm2/sec, cSt).

Grease vs. Oil: A Quick Comparison

At their most basic functionality, grease and oil serve the same purpose: to prevent metal-on-metal contact and protect a piece of equipment from wear due to constant use. However, components within machinery move in various ways and are subjected to many conditions. With that said, here is a run-through of how oil and grease compare as bearing lubricants:

Oil is usually the best choice for high-friction and high-speed applications as it readily dissipates heat, as compared to grease. Being thinner than grease, oil can also flow freely and be easily dispersed. However, components that move vertically or are subjected to heavy loads, often necessitate the use of grease.
Grease is designed to adhere to metal components like wheel bearings and serves to provide a longer-lasting barrier. However, while considering lubrication from oil, the bearing orientation and the lubrication ports should be considered. This is important because an oil may be unable to flow to all applicable raceways and bearings located above the lube ports.
Operating moving parts within a piece of machinery that is exposed to external elements invites dirt and debris to pollute machinery. Greases make a great natural sealant as they prevent harmful contaminants from entering parts of the system, ensuring that machinery performs optimally with minimal faults.
In the case of oil lubrication, some machine builders use a specific misting system. Although such systems are more complicated and expensive than automated or manual grease lubrication systems, an oil misting system contains the added benefit of making a positive pressure environment within the bearing. This not only aids in cooling, but also prevents the entry of contaminants within the bearing.

Wrapping Up

Maintaining an adequate level of lubrication is crucial for achieving an optimum bearing life expectancy, regardless of the type of lubrication used—whether that be oil or grease. Being a leading aviation parts distributor for customers worldwide, we at NSN World guarantee a streamlined supply of premium aviation, electronic, and bearing lubricants, alongside additional parts and components for all of our clients' needs. Get a quote from us today; we can help you source the best and most affordable bearing lubrication system on the market!