Oil vs Oil-Free Air Compressor:

Which Should You Choose?

From inflating car tires on your driveway to running air-powered sanders, drills, and routers in your garage or workshop, there’s no shortage of tasks you can handle when you invest in a good air compressor.

So, whether you want to nail, drill, saw, polish, sand, grind, or clean, it’s just a case of pairing up the right pneumatic tool for the job with any old air compressor, right?

Not quite.

The main decision when you’re looking to buy an air compressor, even before you start looking at the various makes and models available, is whether you should choose an oil-lubricated or oil-free model.

There are significant pros and cons to each.

So, before you go out and part with your hard-earned cash, we thought it would be a good idea to discuss everything you need to know about both types. That way, you can make a more informed decision, and ultimately a wiser investment, when it comes to buying your air compressor.

Quick Links

What Is an Oil Air Compressor?

The Purpose of Oil in an Air Compressor

Why You’d Pick an Oil vs Oil-Free Air Compressor

What Is an Oil-Free Air Compressor?

Why You’d Pick an Oil-Free vs Oil Air Compressor

What Is an Oil Air Compressor?

An oil air compressor is one which requires the addition of pump lubricating oil. The vast majority of air compressors are the oil-lubricated type.

Most oil air compressors used this added oil in a function known as splash lubrication. The oil added flows into an oil sump, from which a dipper on the piston rod dips into the oil in the sump and splashes it onto the moving parts as the piston moves.

Unlike pressure lubrication (a lesser-used alternative to splash lubrication) which uses an oil filter to remove contaminants from the recirculated oil, splash lubrication doesn’t use a filter. Hence, over time, the oil will need to be drained and replaced to remove contaminants and keep the air compressor working as efficiently and smoothly as possible.

an image showing the oil-lubricated Makita MAC2400 air compressor

Oil-lubricated air compressors like the Makita MAC2400 shown above are well-suited for use in the following situations:

In the automotive industry, for example, body shop spray painting.
In the construction industry for use with air-powered tools like sanders or nailers.
For roadworks, for example, supplying moderate-pressure air to power high PSI (pounds per square inch) / CFM (cubic feet per minute) pneumatic tools like jackhammers.
In manufacturing plants located in industrial (rather than residential) areas where noise is likely to be less of a concern.

There are, however, times when using an oil-lubricated air compressor might not be the best choice.

For example:

For domestic requirements like DIY given that oil-lubricated models are usually much larger, heavier, and require more maintenance than oil-free air compressors.
In the food, drink, and pharmaceutical industries where it is critical that compressor oil does not cause contamination by making its way into the end product.

The Purpose of Oil in an Air Compressor

To understand why an air compressor needs oil, you first need to know how an air compressor works.

While there are two main types of compressor, single-phase and dual-phase, both rely on a piston that is driven by either an electric or petrol motor to cause compression.

A single-phase compressor uses a single movement of a piston to pull air from a cylinder that before compressing it once. In contrast, a dual-phase compressor follows the same process, but it compresses the air a second time ahead of sending it to the storage tank.

Both the single-phase and dual-phase types use oil for the same reason, which boils down to the fact that the use of a moving piston as part of the compression process causes friction.

First and foremost, oil reduces the high levels of friction that occur from the metal piston rings sliding against the metal walls of the cylinder at moderate speed. In turn, this also helps to make the compressor much quieter.

The oil also reduces the heat generated from this friction, which, without cooling from the oil, could cause undue stress and damage to critical parts of the compressor.

Finally, the oil also helps to seal any leaks that could lead to air leakage, which would reduce the efficiency of the air compressor.

Why You’d Pick an Oil vs Oil-Free Air Compressor

Here are some of the main reasons why you’d potentially opt for an oil versus oil-free air compressor:

Oil-lubricated air compressors are much quieter

More oil equals better lubrication, which results in quieter operation versus oilless air compressors.

They usually last longer

The additional oil that coats the moving parts of the air compressor provides extra durability and tends to lead to longer lifespans thanks to reduced internal wear-and-tear.

They’re better suited to heavy-duty usage that requires higher PSI/CFM ratings

Oil-lubricated air compressors are better-suited to heavy-duty, professional applications, mainly because the piston and internal components provide higher RPMs in most cases, and this translates a higher PSI/CFM output.

They’re preferable when working in extreme heat and humidity

Aside from providing lubrication, another function of oil is to dissipate the heat which the air compressor generates during regular usage. Oil-free models, despite their permanent internal lubrication coating, don’t experience enough cooling this way, and so they typically rely on the likes of intercoolers for cooling.

Even allowing for intercoolers, oil-lubricated compressors still tend to heat up more slowly and reach an overall lower temperature, making them the preferred option in hotter climates.

What Is an Oil-Free Air Compressor?

The term ‘oil-free’ isn’t entirely accurate.

All air compressors, the oil-free type included, require some form of lubrication to reduce the efficiency-sapping friction that increases heat, creates noise, and leads to wear-and-tear of key components within the compressor.

Unlike oil-lubricated air compressors that use oil added to the sump to lubricate the cylinder and piston, though, so-called oil-free air compressors like the Bostitch BTFP02012 shown below use an internal coating that acts as a permanent source of lubrication that, in theory, doesn’t need replacing.

In a lot of cases, the coating applied is Teflon.

an image of the Bostitch BTFP02012

Here are a couple of situations where using an oil-free air compressor would likely be preferable:

For DIY around the house given that oil-free compressors are usually much smaller, lighter, and they require more maintenance than oil-lubricated models.
In the food, drink, and pharmaceutical industries where it is critical that compressor oil does not make its way into the end product.

As always, nothing is perfect, and here’s where an oil-free air compressor might struggle versus an oil-lubricated model:

For heavy-duty jobs in commercial and industrial applications, mainly because oil-free air compressors tend to have smaller storage tanks and shorter overall lifespans.

In most cases, they aren’t able to produce comparable PSI/CFM ratings as oil-lubricated models, either, meaning they might struggle when tasked to power heavy-duty air-powered equipment.

Why You’d Pick an Oil-Free vs Oil Air Compressor

Here are some of the main reasons why it might make more sense to opt for an oil-free versus oil air compressor:

Oil-free air compressors reduce the risk of contamination

When used in the food industry, for example, the absence of any added compressor oil means that there is one less substance that could potentially contaminate the end product.

They’re cheaper

Oil-free air compressors are simpler in design, and they are more straightforward to manufacture as a result of having fewer moving parts. Both of these factors combine to make them cheaper versus oil-lubricated models.

They weigh less

As above, oil-free air compressors generally have fewer moving parts, and so, across comparatively-powered models, they’ll be lighter than oil-lubricated compressors.

They require less maintenance

Their simple design and use of fewer moving parts mean that there’s usually less to go wrong in oil-free air compressors. Also, they don’t require any periodic topping-up or changing of oil, making them easier from a maintenance perspective.

They’re preferable when working in extreme cold

The colder it gets, the thicker the oil in an air compressor becomes. As it thickens, the lubricating capabilities of the oil become considerably reduced, leading to more wear-and-tear and a shortened lifespan for the air compressor.

Oil-free models typically perform much better in extreme cold, making them the preferred option for these environments.

Final Remarks

As you can see, there are plenty of pros and cons when it comes to both oil-lubricated and oil-free air compressors.

If you’re a homeowner or DIYer looking to complete odd-jobs around the house, for example, inflating tires, blowing leaves out of gutters, and using the odd air-powered tool like a drill or sander, we’d recommend going with an oil-free model.

In these situations, oil-free air compressors should still provide sufficient PSI/CFM ratings to tackle lighter tasks, and you’ll benefit from an air-compressor that’s smaller, lighter, and requires less maintenance.

For heavy-duty requirements, for example, running high PSI/CFM pneumatic tools like jackhammers, or for commercial businesses requiring significant volumes of moderate-pressure air for sizable industrial processes, an oil-lubricated model could be best providing the risk of contamination, additional noise, larger compressor size, and added maintenance do not prove problematic.

Hopefully, we’ve helped you figure out which type of air compressor is right for you, and why.

Remember, if you do have any questions or queries, or require any advice, leave us a comment below and we’ll get back to you as quickly as possible.

Good luck!

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