What is Air Compressor Oil?
Air compressor oil is a lubricant used to prevent wear to the moving parts in compressors, exactly as with any other internal combustion engine. They can be synthetic or natural (people have even tried to run compressors on vegetable oil) and they also differ in terms of the additives they contain. There is less sulfur and carbon in it, and there is no detergent in it, contrasting it greatly with motor oil.
In addition to the lubrication compressor oil providers, it offers numerous other benefits for compressor use, including:
- Extended lifespan: Air compressor oil additives also extend the lubricant’s life, protect machine components in standby mode and make the lubricant compatible with various environmental conditions.
- Thermal absorption: The oil in the compressor absorbs heat produced by compressed air, reducing the operating temperature.
- Good cold temperature viscosity: While some oils lose their viscosity when temperatures drop, air compressor oil retains its viscosity even in cold weather.
- Rust protection: Oil additives delay acid formation and oxidation by delaying the process of oxidation.
- Demulsification: Oils for air compressors contain additives that improve water separation, preventing them from emulsifying with water and oil. This makes it easier for the oleophilic bags to capture the oil later on.
- Ability to prevent foaming: When big air bubbles rise to the surface of oil, foam can be created. Because of this, the oil’s surface becomes more exposed to oxygen, increasing oxidation. A lack of anti-foaming additives would result in foam saturated oil separators and a diminished compressor life. This is due to the effects of saturated oil separators, which create a pressure drop and require more energy to operate.
Do air compressors need oil?
Yes and no. Like most engines, air compressors use oil to lubricate the internal parts of the engine. The oil will also help maintain a cool temperature inside the unit. If a compressor does not have enough oil then it could overheat and cause severe damage to its motor which would render it useless. However, there are oil-less air compressors which require none at all (see belo).
Oil Free vs Oil Air Compressors
When it comes to choosing the right compressor, there are many different options. The type of work you will be using it for determines which type is best for you. Oil-less air compressors can be cheaper in the long run but they will not have as much power. Oil air compressors use oil and do not require periodic maintenance as often, but they may cost more in the long run.
Splash Lubrication / Oiled Compressors
These are the most common type of compressors. Splash lubrication is exactly what it sounds like. Normally, compressor lubricant (such as oil) is sprayed up into the moving parts of these compressors by rotating dippers shaped like flat spoons attached to the bottom of the connecting rods.
An oil-free compressor does not use oil for lubrication. Rather, their wearable parts are coated with special friction-reducing chemicals, which self-lubricate for the entire life of the compressor.
Advantages & Disadvantages of Oiled Air Compressors
Oiled stationary compressors are the industry standard and are often found in a shop or garage where high pressure and volume keep all of the tools in operation throughout the day. If maintained well you will years and years of use out of them.
- Great for industrial or professional use
- Generally more powerful
- Higher PSI/CFM ratings due to increased RPM
- Can be used in hot weather but struggle in cold
- Tend to be heavy & not as portable as oil-free
- Regular maintenance needed
- Oil can contaminate the air
Advantages & Disadvantages of Oil-Free Compressors
An oil-free compressor runs at a lower RPM, which reduces noise, heat, and friction, thereby extending a pump’s service life. This, in combination with better castings/exact tolerances and friction-reducing coatings, makes an oil-free compressor an excellent choice in numerous applications.
- No oil contamination in air
- Tend to be lighter and more portable
- Almost 100% maintenance free
- Oil filters not needed
- Work well in cold weather
- Runs cooler, quieter and more efficiently
- Not as powerful
- Not suitable for running all day, e.g. in a professional setting
How do I check if my air compressor needs oil?
To make sure that your compressor does not run low on air compressor oil, you should inspect it 3-4 times a week. You can use either the dipstick or sight glass to check the oil level in the compressor.
All dipsticks in air compressors are calibrated. It’s important to make sure that your oil level is always near the max. However, some sight glasses are not calibrated so take care using these. In order to ensure a good level, ensure that the oil level on the sight glass is 2/3 full.
How often should you change the oil in your air compressor?
An air compressor‘s oil changing schedule differs significantly depending on its type. Depending on the machine, it may be necessary to change the compressor oil more often than others. It is best to consult the user’s manual that comes with the oil package you have purchased for further information on this. Instruction manuals may even provide information about the expected life of the oil based on the service hours.
If you cannot find your user’s manual, we have provided some basic guidelines for compressor types’ oil change schedules:
- In Rotary Screw Compressors, the oil should be changed every 1000 to 2000 hours of operation.
- In Reciprocating Air Compressors, the oil should be changed every 3 months.
It is recommended to change air compressor oil every 3,000 hours or 2500 hours depending on the compressor‘s model, but you should change the oil in your unit once per year as a bare minimum. Generally, oil filters are only commonly found in larger models where the oil is regulated, so for most domestic home shop air compressors, you should change the oil as soon as the machine is opened.
What type oil for air compressor?
With air compressors, there are two main types of oil – lubricating and hydraulic. Lubricating oil is used to reduce friction and maintain the internal parts while hydraulic oil is used for lubrication in the pump.
If your compressor is still under warranty, then you should use the oil that the manufacturer recommends. An oil recommendation will usually be found in the compressor‘s manual/guidebook. A hardware store should be able to sell you lubricating oil if the warranty period for your air compressor has expired.
The rule should only be applicable to DIY compressors at home. Compressors used in industry – rotary screw, reciprocating, etc. – have specific oil requirements because they are more sophisticated and larger than ordinary compressors. By using the incorrect oil, you will risk damaging the machine or voiding the manufacturer’s warranty.
Mineral oil or synthetic oil: Which is better?
How often and continuously you use your compressor determines what kind of oil you need.
Synthetic or mineral oils can be used for air compressor oil lubrication, but mineral is usually the oil of choice for compressors.
Synthetic oil and mineral oils are both lubricants that reduce friction between moving parts. The lubricants typically contain hydrocarbons dissolved in mineral oils or synthetic oils. Mineral oils are typically derived from petroleum, whereas synthetic oils are typically made from esters.
Make sure you carefully consider your choices before selecting one. The type of work you intend to do with your compressor as well as the amount of use must be considered before choosing either mineral or synthetic air compressor oil.
You can opt for standard oil over a heavy duty lubricant if you don’t intend to use your compressor continuously, because it is ideal for working with light to medium-duty compressors. In addition, these oils are cheaper than synthetic.
Synthetic lubricant may be more appropriate for industrial use, where your compressor is constantly on. Synthetic oil is said to make compressors run smoother and quieter. Synthetic oils also have a higher temperature range and are more resistant to overheating than conventional oils.
The reciprocating and rotary screw models can be operated with various kinds of oil products, but synthetic oils are often recommended because they do not contain sulfur or other additives that can cause valve buildup.
Synthetic compressor oil also has the following benefits for rotary screw air compressors:
- Extended lifespan: Synthetic oil can increase the life of your rotary screw compressor by up to 8,000 hours.
- Reduced deposits: Synthetic oils inhibit varnish and sludge, which can lead to premature compressor wear and tear.
Air compressor oil vs motor oil
Motor oils are designed to lubricate and protect internal engine components, while air compressor oils prevent moisture from accumulating in air lines and cylinders. But don’t ever be tempted to put motor oil in your compressor! They may seem similar because in essence, compressor oils are just non-detergent oils specifically designed for compressors.
However, motor oil (for your car or truck) will generally contain detergents, which are useful for internal combustion engines, but for a compressor it is not going to be a good idea since it will actually cause a lot more carbon build up over time.
It is generally better to use the specific compressor oils, especially if you wish to follow the air compressor manufacturer’s warranty guidelines. If you take your compressor in, and they determine you have been using a non-specified oil, this will void the warranty and any benefits it might have provided.
Using a non-detergent (20 or 30w) motor oil for your compressor is a potential alternative, but most people will not have this in their home shop, so you might as well just purchase the oil that is specifically designed for your unit.
Air compressor oil substitutes
We have discussed the use of non-detergent motor oil in compressors above, but there are some other substitutes for air compressor oil, but again, we would always recommend using dedicated air compressor oil over any of these options. The most common substitutes are a combination of light mineral oil, kerosene, and petrol. Other options include vegetable oils or automotive fluids.
ATF oil in air compressors
ATF is Automatic Transmission Fluid and is mainly used for an auto transmission, but could also be used in a compressor. Their benefits include reducing wear and tear, preventing breakdowns, and cooling parts which is useful because during operation air compressors produce a significant amount of heat.
The ATFs’ ability to resist breakdown will help ensure that your compressor operates effectively without overheating causing it to fail. The majority of ATFs, however, are incompatible with compressors and can damage them so please use a dedicated air compressor oil if you can.
Hydraulic Oil in air compressors
There are some characteristics of this oil that make it suitable for use in air compressors. Since they have a low density, they have a low viscosity at low temperatures, which allows them to flow more freely – which is best for compressors. In colder climates, hydraulic oil is probably the most suitable alternative oil. Moreover, since these oils are resistant to corrosion, they can prevent rust on your compressor.
What are the main properties of air compressor oil?
There are a whole range of properties of compressor oil that we could go into, but I’ll cover off the 3 that are of main concern when selecting a compressor oil:
- Additives used
- It’s Operating Temperature Range
- Viscosity of the oil itself
Additives in air compressor oil
Adding chemical additives to oil imparts properties that the oil underlies is not capable of delivering.
As an example, motor oils typically have a detergent component that helps to prevent the build up of carbon deposits – and thereby stop the accumulation of carburized oil happening at all.
Typically, compressor oils contain more additives that act as preservatives to prevent rust and corrosion within the machine. Some mid-range compressor oils also contain additional lubrication, or “anti-wear additives.”.
Compressor oils see relatively high temperatures under constant use, which makes anti-oxidation additives one of the most important additives. In addition to reducing oxidation, this anti-oxidation additive also promotes oil stability.
Essentially, these additives all sacrifice themselves for the sake of oil stability. In effect, over time, these additives lose their potency within the oil, so the oil essentially reverts to its pre-additive state, but much more oxidised than previously – which obviously is not good for metal part. Therefore, it is imperative that you change your oil for fresh even when the oil level looks ok.
This is also another reason why it’s imperative to completely change compressor oil instead of constantly topping it up. Otherwise, you are causing old, degraded oil to mix with the new and lovely additive-enriched oil.
Nowadays, modern oils tend to have more consistent viscosities within the SAE20 to SAE30 range, even though oil of much higher viscosity levels is still available, they are less often used in machinery.
Air compressor oil is no exception – SAE20 or SAE30 oils are ideal for them too. The SAE20 or SAE30 air compressor standards aren’t even that different to be honest – at least not enough to mean that you should use one or the other.
Due to SAE20’s slightly lower viscosity, it will operate a little more efficiently at colder temperatures than SAE30, as it will create less drag on the engine.
The SAE30 oil has a slightly higher viscosity (thickness) than SAE20, so the oil may not run as efficiently at colder temperatures. Therefore, using SAE30 at lower temperatures results in a slightly less efficient compressor.
Oil of SAE30 grade retains its lubricating properties better in temperatures above or equal to 30°C than oil of SAE 20 grade. At lower operating temperatures, SAE 20 compressor oil will have a thinner viscosity (it will thin out).
So as you can see, the usual operating temperatures the compressor will be running in is what defines the oil you choose. However, it will only make a real difference to compressor users who are operating their equipment every day or continuously.
Remember that both SAE20 and SAE30 compressor oils are reduced in viscosity by the heat generated during operation as the engine runs. Under sustained conditions of lower temperatures, SAE 20 oil will outperform SAE 30.
Operating Temperature Range
Heat denatures and oxidizes all oil types, not just compressor oils. The higher the temperature, the faster the oil oxidizes, which causes it to lose its intended lubricating and protecting properties.
Special oils are often needed for extreme low or high temperatures, such as those below freezing or above 100-120 degrees Fahrenheit. So usually, your air compressor manufacturer will have advised the normal operating temperature for your unit in the user manual.
The oil inside your compressor’s engine will have to endure much hotter temperatures than the ambient atmosphere due to the fact that it also generates heat as it operates. The manufacturer’s temperature range for your compressor won’t, therefore, also be applicable to the oil inside your compressor.
For further information, refer to your machine’s manual. But – a specific range for the compressor oil temperature may not be specified in it. It’s not a cause for concern if you’re still unsure about whether the oil you have will work, as most compressor oils are designed to function in typical operating temperatures. If you are unsure of an oil, speak with your local workshop equipment dealer.
Does oil have an expiration date?
Yes, once oil reaches an expiration date, its performance levels no longer can be guaranteed. The heat and pressure of long-term operation over thousands of hours can oxidize the oil, which causes it to thicken and lose its ability to move around the system. Additionally, as debris continues to accumulate, the part of oil that contains contaminants will become less effective. So, be sure to change it regularly so that doesn’t happen.
How to change oil in an air compressor
Don’t worry, changing oil in a compressor is a relatively simple process. You can do it in just a few easy steps:
- Let your compressor cool down by unplugging it and turning it off
- Ensure all remaining oil has been drained from the compressor
- Fill the drained oil reservoir as needed. Make sure you wipe up any overspill
- Ensure the filler cap is fully tightened
- Plug the compressor in again, and switch it on
What happens if I do not put enough oil in my air compressor?
Insufficient oil causes your compressor to break down more easily. The machine runs smoothly because of oil, so if there is not enough, the machine overheats and can damage its engine. However, if you have just put oil in, the chances are it will be OK – it is more likely that you will put too much oil in if you are in the process of filling it up! If you’re unsure, just check the level with the dipstick or a sight glass, as mentioned above.
Can you put too much oil in an air compressor?
Yes, absolutely! You can cause significant internal damage to your compressor by filling its oil sump to the top. Oil that becomes aerosolized from the compressor‘s discharge can cause damage not only to your compressor, but also to any pneumatic tools and accessories attached to your compressor. You may have to scrap and rework your entire project because of oil discharge – for example, the application of finishes, paint, or sanding would be ruined by oil entering the air.
What happens if you put the wrong oil in air compressor?
If you fill your air compressor with the wrong type of oil, it can become damaged. Make sure to only use the recommended type of oil for your machine. If you have accidentally filled it with the wrong oil, then don’t worry – you simply have to follow the steps outlined above in the section titled ‘Changing oil in an air compressor‘, which is simply a matter of draining out the wrong oil, and filling it up with the correct fluid (e.g. specific air compressor oil). Don’t worry about mixing – there will be so little of the old oil left after draining that it won’t matter.