I am often surprised by how much debate there is about what kind of lubricant to use where. In a way, this debate is a natural result of the wide range of applications and environments in which grease or oil can be used. Many of our customers, and potential customers, will test dozens of products before they find something that is just right for their new widget. You can read this entire post, but if you just want a good rule of thumb to follow, here it is:
If the system is self-contained, well-sealed, would be difficult to grease and does not have vertical loading, use oil. If the lubricant cannot be contained by the design, is not naturally dispersed in the application, has vertical loads, and benefits from have the lubricant be a barrier to the environment, use grease.
There are a few key indicators that you need grease:
1. Use grease for low speeds and high loads
a. Grease will prevent “Dry Starts,” which occur when the oil has settled out of spots during downtime on the equipment. Grease often contains extreme pressure additives that will prevent the surfaces from touching despite high vertical loading. It is true that oil can fill space quickly in high-speed applications, but in a low-speed application grease is the clear winner.
2. Use grease on areas that need lubricants to STAY PUT, such as semi-exposed surfaces or areas where oil would easily leak out.
a. Remember: Oil will move with gravity, the right grease will not.
b. People often think that grease will attract more contaminants than oil because it is stickier. The reality is that there is nothing about grease that attracts more contaminants than oil. The only reason you may have less contaminants is that the oil has evaporated or migrated from the surface and there isn’t anything for the contaminants to stick to. You are much better off using a grease lubricant that will maintain an even film and not migrate.
3. Use grease when you need certain performance enhancements. Oil often contains many performance-enhancing additives, but certain additives tend to settle out or not work in the first place.
a. Grease should be used in cases where extreme pressure, corrosion resistance, and longer-term lubricity are essential.
Keep in mind that this is not an exhaustive list. There are many times when application or product-specific benefits change these dynamics, but this narrative has been simplified for the sake of the comparison.
You may think that as a manufacturer of lubricating greases, I have an obvious bias in this debate. I am, however, the first person to admit that there are billions of surfaces that require lubrication and one solution will never work for every application. So, even though I have a predisposition to grease, I can still serve plenty of customers without claiming grease is superior to oil in every way.
In fact, oils will have some key advantages over grease:
1. Oils will act as a medium for heat transfer
2. Oils will perform better at extremely high speeds
3. Oils are easily inspected in the field
4. Oils can be filtered to remove contaminants
This is a fairly condensed list because there are a few advantages that are debatable. For instance, some people will claim that there are fewer risks of compatibility problems when mixing oils, and changing oil is easier, but this is not always true. Thus, we have left our advice fairly general, and encourage you to contact us or to comment on the blog. Then we can better address nuances in lubrication selection as they come up.
