What’s the Difference between Motor and Compressor Oil?

If you have an oil-lubricated air compressor, the owner’s manual will tell you to use compressor oil, not motor oil. But, does it REALLY matter? It turns out it does - we’ll tell you why in this episode!

#compressors #compressoroil #compressedair

The manufacturer of your oil-lubricated air compressor tells you that you must use compressor oil specifically to lubricate your unit’s air pump. Is this just a strategy to sell another product and one that is more expensive at that?

Nope, there are legitimate reasons to use the specified compressor oil. While it’s true that both combustion engines and compressor pumps generate high levels of heat, the source of that heat is different. Heat in the combustion engine comes from combusting fuel. Heat from a compressor pump comes from pressurizing air and to some degree (pun intended), friction.

Compressor oil is formulated specifically to have the correct viscosity to keep operating surfaces inside the pump lubricated, even during start-up and immediately after beginning operation. Besides that, pressure builds up inside the pump significantly more than the “lower half” of a combustion engine, so the oil needs to stay fluid and in place, even under high pressures. Compressor oil does that very well and greatly reduces wear and tear on the compressor pump’s moving parts.

Compressor oil is almost always non-detergent. Detergents are added to regular motor oil to keep soot (a by-product of combustion) in suspension, as well as other impurities, including water. Some detergent additives also help control the acidity that forms in the base oil. Acid inside a combustion engine is not a good thing! Why wouldn’t detergent be a good thing in a compressor pump? Detergent also can more readily lead to emulsification of the oil - when oil and water are blended by continual agitation - much like oil and vinegar in your favorite Italian salad dressing. That’s great in a salad, but not in a compressor pump. Because the water and oil won’t readily mix in the absence of detergent, the water settles out in the base of the oil sump (water is heavier than oil, oil “floats” to the top as seen in oil-slicks) and is easily drained off during an oil change.

Keeping small particles in suspension isn’t good either inside an air pump. It’s better if they separate out instead of clogging up minute passages in the pump and components.

Most small to moderate-sized compressors have their pumps cooled by air - but that’s only part of the cooling system. The oil itself is a component of the cooling system. Compressor oil is formulated to provide efficient cooling and heat dissipation. This helps maintain the best operating temperatures - thereby prolonging the life of the compressor.

With compressor pump oil being changed out at the recommended service intervals, and the break-in oil in a new compressor pump being changed after about 20 hours of operation, you can expect many years of service from your unit’s compressor pump.

While you could use regular motor oil in your compressor pump, and you wouldn’t see immediate side effects, why do that? You’ve got an investment in your compressor, so take care of it by using the specified lubricant and get a longer-term return on your investment. It’s a wise decision.
Oilless air compressors are becoming more available and are increasingly popular. But, what are the trade-offs between oiled and oil-less compressors? Check out this episode where we demystify the two types and give you the information for you to make your own decision:

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We’ve installed a moderately sized single-stage compressor in our shop, that utilizes an oiled compressor and large cooling fan. It’s the DeWalt® DXCM303. We think it’s a great compressor for the price and fits well in a small to medium-sized shop environment. You can check out our product overview here:

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When we’ve had the DeWalt®DXCM303 Single-Stage Compressor in service for over a year, check out our review on how it held up and is performing here:

COMING AFTER ONE YEAR OR MORE OF OPERATION!!!

We like the DeWalt® DXCM303 Single-Stage Compressor, but some after-market enhancements make it easier to service and run better. Check out our “Pimp My Compressor” episode here:

COMING SOON!