Friday, October 27

Air Compressor Oil 101: All the Basics You Should Know

Read the following blog post to learn about air compressor oil & lubrication.

Oil-Lubricated Compressors

Most industrial-grade air compressors rely on lubrication to operate efficiently. They utilize oil to lubricate their internal parts and carry-out its job smoothly. In lubricated air compressors, oil mixes with the air during the compression process and then gets separated away from the air before the air is released for use. There are a few main kinds of oil-lubricated compressors:

Why is Oil Used in My Compressed Air Equipment

Oil is used for many different reasons in your air compressor but mainly as a lubricant for all internal moving parts. Without this oil, the mechanical components will create friction that causes inefficient and rough operation that can create a risk for damage. Here are a few functions that oil performs.

Friction Reduction

As discussed above, oil is used as a lubricant to reduce friction between the moving parts. This both enhances operating efficiency while reducing wear and tear. Friction reduction also decreases the noise your machine makes, creating quieter operations.


Oil injected into your system helps prevent overheating by cooling the air during compression.


Rotary screw compressors utilize oil to create a seal between the rotors to trap the air inside for the compression process.

Cleaning & Corrosion Prevention

Oil circulating through your compressor helps clean the system by capturing small particles from the compressor. This oil also contains certain rust and corrosion inhibitors that help protect the metal components from damage that can occur from moisture or other contaminants entering the compressor system.

Types of Oil

Oil can be defined by its viscosity, or grade, to categorize the kind of oil it is. Viscosity is essentially the thickness of the oil. The higher the number, the higher the viscosity, and thus the thicker the oil. Thickness of the oil can determine how your compressor will perform in various environments. For example, cold temperatures can cause a freezing effect to certain oils, causing them to form a sludge like substance. In these instances, a lower viscosity oil would be preferred. There are two main categories of oil that both use these viscosity ratings to differentiate between types:

Standard Oil

Standard air compressor oil is made from a mineral oil base. It is the least expensive option but has shorter lifespan due to a few factors. Standard oil breaks down faster and converts to vapor, requiring more frequent oil fills and replacements. This vapor that is created can get past seals that are put in place to keep the liquid oil out of the air chamber. This is unavoidable in oil-lubricated pumps, but the more it happens, the more the air/oil separator filter will need to be replaced.

Synthetic Oil

Synthetic oils are made with a synthetic base, which means it is an artificial blend of some kind. This is in comparison to the mostly petroleum-based blend that is in standard oils. Synthetic air compressor oil is more expensive than standard oil, but it can last up to 50% longer. This is because it doesn’t break down and evaporate as easily or quickly. It also provides greater cooling effects and has enhanced capabilities when removing deposits from the pump components. Therefore, synthetic oil requires less frequent filling and replacements. There are a few common synthetic blends that are used in air compressors:

  • Synthetic Hydrocarbons (POAs)
    This is the most common synthetic lubricant used for industrial air compressors. It is derived from ethylene, meaning it has natural gas or petroleum in the mixture. POAs are engineered to be a good multi-purpose air compressor oil due to its high stability, low volatility, and uniform flow throughout a wide temperature range.
  • Polyol Esters (POEs)
    This is the second most common synthetic air compressor lubricant. It is derived from alcohol and carboxylic acid to provide strong thermal stability, longer life spans, and ability to mix with other lubricants. This mix helps to keep lubricated parts clean, but due to its contents, can damage certain paints or finishes and can have reactions with various rubbers and plastics.
  • Polyglycols (PAGs)
    These lubricants do not oxidize and create varnish on the interior of your air compressor. They are, however, difficult to separate when mixed even if it is with water. This can cause a reduction in viscosity over time as more moisture and water gets mixed into the lubricant. While PAGs can mix with other ingredients and lubricants, they should not be mixed with POAs or standard oils as it can damage your compressor.
  • Blend of Synthetic & Standard
    Many people will use a mix of Synthetic Hydrocarbons and mineral oils as it can be more cost effective. This type of oil is generally used in applications that require more frequent oil changes since standard oils become more susceptible to thermal breakdown and oxidation when combined with synthetics and exposed to extreme temperatures air compressors generate. This also can lead to quicker development of varnish, requiring the oil to be changed regularly and more frequently.
  • Food-Grade Oils
    These oils are synthetic oils that are specially engineered to be non-toxic so that the compressed air that may encounter food will not contaminate the food products. These are frequently used in food packaging applications.

Which Oil Type Should I Use In My Air Compressor?

Each specific air compressor comes with its own manual that recommends the type and grade of oil you should be using. Most compressor manufacturers will give you the option between standard or synthetic but give you a viscosity rating to follow. To determine which to use, you need to understand your intended compressor usage and how often and long it will be operating for. In general, standard oil is best for light to medium duty applications, while synthetic is best or heavier duty, continuous applications.

Can I use the Wrong Compressor Oil Type In My Air Compressor?

Yes, using the wrong oil in your air compressor can cause a plethora of problems including lack of ample lubrication, collection of varnish & deposits within the system or the airend, and increased wear and tear that shortens your equipment’s lifespan. This also includes mixing the wrong lubrications together within your system.

If you do happen to fill your compressor with the wrong oil type…

Make sure to flush it out of the system completely as soon as possible. Once the wrong oil is flushed out, replace it with the correct lubricant and start your operations as normal.

How is Air Compressor Oil Different From Motor Oils?

Technically, you can use motor oil to operate an air compressor, however, this doesn’t mean that you should. Motor oil contains detergents that can lead to the buildup of unwanted carbon deposits within your compressor. Air compressor oil has been specially engineered to contain no detergents to ensure efficiency, peak performance, and longevity of your compressed air system.

The Role of Oil Water Separators 

Oil water separators are exactly as they sound- a part that separates the water from the oil that needs to be used as lubrication inside the compressor. All lubricated compressors come with an internal oil-water separator, but you will want to add an external one to your system as well. During the compression process, outside contaminants (such as water) can get mixed in with the oil, and thus contaminate the air. Once this contaminated air cools down and forms condensate, this moisture can collect throughout the compressed air system and cause damage to your compressor or final products. This condensate that forms is unavoidable, so it is important to add an external oil-water separator to remove this condensate from re-entering the lines and the clean oil.

Maintenance for Oil-Lubricated Air Compressors

Add Oil

Each compressor model requires a different amount of oil depending on the type and size. Either refer to your user manual, contact the manufacturer, or contact a compressed air expert like Zorn Compressor & Equipment to ensure you know the amount of oil your compressor needs. In general, air on the side of caution when filling the reservoir for the first time. It is better to underfill the compressor and add more oil if needed than it is to overfill and remove oil. However, operating your compressor at too low an oil level can also cause damage, so make sure there is enough oil to properly lubricate the parts when operating initially.

What Happens If I overfill The Reservoir?

Overfilling your compressor’s oil reservoir can lead to very severe consequences. When the oil reservoir is overfilled, the excess oil can cause the compressor to “spit” oil or can leak into the air system and contaminate your entire compressed air supply. This not only can contaminate your end product, but it can damage crucial internal components as well. This can lead to costly repairs or replacements that ultimately can lead to compressor downtime and lost production. If this does happen, contamination won’t occur until the pump is turned on. So, if you do overfill the reservoir, make sure to open the drain plug and let some oil out before turning your compressor on.

How To Check the Oil Level

Most oil reservoirs will feature either a dipstick, like in your car, or a sight glass for you to view where the oil level is at. If the oil level is at or near the center of the sight glass or at or near the “add oil” marker level on the dipstick (it should be clearly marked) this is when you should add more oil to ensure efficient operation of your air compressor. In general, you should not let your compressor oil reservoir reach the “add oil” levels. You should try to keep it as close to max full as possible, rarely dropping below 2/3 full. Rapidly decreasing oil levels can indicate a leak and you should call an expert to service your compressor immediately. You should check your oil level a few times per week.

Change Oil

Each compressor type requires a different schedule for changing out your compressor’s oil. Depending on your oil type, compressor usage, and environment, this may need to be more or less frequent. Always consult with an expert to work out the best oil change schedule.

Oil Sampling
Oil sampling is a process that takes a small amount of oil from the compressor’s oil reservoir and tests it to analyze its condition and find any potential issues. This process will indicate whether the oil should be changed or if additional maintenance is required. Each compressor requires a different frequency for oil sampling. A baseline to follow would be sampling the oil every six months at a minimum or, for rotary screw compressors, after every 2,000 hours.

How to Know When to Change Oil
A few aspects of your oil can indicate it’s time to swap it out for fresh, new oil:

  1. Oil has become thick and/or opaque.
  2. Oil has a discoloration that strays from its normal hue.
  3. There are visible particles or contaminants.
  4. The oil has a bad odor.

Whether one of these indicators is observed or not, oil should be changed a minimum of once a year. This is also regardless of conditions and hours of operation.

How to Change Oil
Follow these steps to safely change your air compressor’s oil:

  1. Turn the air compressor off completely & disconnect it from the power source.
  2. Remove the drain plug and drain any existing oil.
  3. Follow your local industry regulations and dispose of the used oil safely.
  4. Refill your compressor with the right amount and the proper oil type.
  5. Confirm you have reached the proper oil level by viewing the dipstick or sight glass. If it is not at the right level, add or remove oil as necessary.

Clean/Replace Oil Filters

Oil filters help to remove excess particulate from the oil before it gets recirculated for use in the compressor. As a general rule of thumb, you should be replacing or cleaning this filter every time you change your oil. This could be more frequent depending on the amount of particulate that is being collected so it is important to keep an eye on the condition of the oil filter throughout use.

Check Oil/Water Separators

You should be checking your oil/water separators weekly to ensure they are operating properly. These units have a range of when they need to be changed based on hours of operation and intensity of use. It can require changes anywhere from quarterly to annually but should certainly be changed once a year at a minimum.

Reduce Oil Carryover

Due to the heat generated from a compressor while operating, small amounts of oil can turn into aerosols and enter the air supply. Using an inline filter can reduce the oil carryover as it removes both oil aerosols and particulate from the compressed air supply.

Prevent Varnish

Varnish forms as the oil breaks down and forms a new sticky, thick material that can accumulate and harden on various surfaces within your air compressor. This, of course, can cause a plethora of problems that can add up to severe consequences. To prevent the formation of varnish it is critical to use the proper oil type in your compressor, maintain proper temperatures so that your compressor does not overheat, and regularly check and change your oil. If your system does develop varnish, there are different cleaners you can run through the system to remove the varnish buildup. Always consult a compressed air expert before using one of these cleaning treatments.

Zorn Compressor’s Lubricant Offerings

Zorn Compressor & Equipment has access to all OEM lubricants for the machines we sell. In addition to OEM options, we also stock premium Zorn Private Label lubricants to make sure your air compressor receives the highest quality lubricant for smooth operation. Below is a list of our Zorn stocked lubricants:




Zorn is the Midwest leader of custom, engineered compressed air and vacuum solutions. We provide the best customer experience by understanding your applications and needs and offering an unparalleled commitment to customer satisfaction. 

Our comprehensive product and service solutions keep you running 24/7.

  • Reliable equipment
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  • Local, 24/7 service

Our compressed air experts look forward to meeting you to discuss your equipment and support needs. Please contact us directly at (262) 695-7000 with any questions or to schedule service for your system moving forward.

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