If your compressor is due for an oil change, you may ask the question: can I use motor oil in my air compressor? If you’ve visited many forums online where this same question has been discussed, you’ll notice that many have said they’ve used motor oil in their compressors without any issues. The reality is, they’re lucky to not have experienced problems. There is the obvious temptation, for the sake of convenience, to use the spare motor oil lying around in your shop. However, this can prove to be a detrimental mistake for your air compressor, which requires its own specific type of high-performance lubricant. Long-term, we propose that a better strategy is to choose a specially formulated air compressor oil. Here’s why…
Car engine motor oils are formulated specifically for that application. Chemists utilize specific additives designed for specific issues the oil must contend with. Such additives are detergents, dispersants, viscosity improvers, etc., not to mention the base oils. Because automotive engines burn fuel, that fuel can cause issues with motor oil, thus an engine oil is designed to deal with those issues. An air compressor, however, operates in a different environment and certain additives used in motor oils are not helpful, and in fact, can be harmful to an air compressor. Eventually, motor oils used in air compressors can start to develop carbon deposits. Certain air compressors, namely screw compressors, tend to have issues with water buildup. As you may know, water and oil don’t go together and can cause emulsification, which can reduce or remove any lubricating or protective characteristics of a motor oil. So, to get back to the initial question: can I use motor oil in my air compressor? All technical reasons, based on manufacturers recommendations and real-life experiences, point to choosing air compressor oil over motor oil.
Air compressor oils are formulated differently from motor oils. When formulating air compressor oil, detergents and sulfur are left out so as not to allow the formation of harmful deposits from building up on the compressor’s critical component surfaces and valves. A high-quality air compressor will utilize the newer generation of base stocks that have been tested to perform as required for the compressor. A high-quality air compressor oil will be formulated with a robust quantity of antifoaming, antioxidation, antiwear, and antirust chemistry.
There are various types of air compressors, such as reciprocating compressors, screw compressors, and flooded vane compressors. Typically, a reciprocating compressor will call for an SAE 30 for both the valve side of the compressor and the crankcase. If the reciprocating compressor is operating in colder weather or colder conditions, you may need to drop down to an SAE 20. By choosing to use a high-quality air compressor oil, the crankcase valves, rings, and cylinders will stay clean and allow the compressor to operate problem-free without the fear of deposit buildup. For a screw compressor, the rotors never touch or come in contact with each other. Screw compressors tend to run cooler and generate less heat than a vane compressor. Because of these lower levels of heat, temperatures are reduced and compressor oils tend to last longer. Depending on the manufacturer of the screw compressor, the following viscosities are typical for this type of compressor: SAE 10, SAE 15, and SAE 20. Flooded vane compressors operate in a severe environment. They are designed to develop high rotational speed, which naturally creates quite a bit of friction. There is quite a bit of heat that is generated in a flooded vane compressor, and because of the high rotational speed, there is a tremendous amount of shearing action. It is even more critical to choose a heavy-duty air compressor oil. Look for a compressor oil that utilizes thermally stable base oils along with high-performance antioxidation additives. A flooded rotary vane compressor typically calls for an SAE 20, SAE 15, or SAE 10. As a side note, because of the high shearing action of a flooded vane compressor, a multi-viscosity motor oil such as a 10W30 would be a perfect example of why motor oil would be a very poor choice for this type of compressor. Multi-viscosity motor oils utilize viscosity improvers, which tend to be sensitive to shearing. In a very short time, this motor oil would fall apart.
Properly formulated air compressor oils are designed with what is known as demulsibility. This means the oil will not emulsify with water, or in other words, stays separated from the water. This demulsibility characteristic is another example of how an air compressor oil differs from motor oil. Through extended air compressor running, there is a possibility of water being introduced into the system, whether through condensation, leaks, or other sources. This water could create damaging problems to the compressor via rust or worse, changing the characteristics of the oil. For this reason, utilizing an air compressor oil that offers demulsibility will protect all critical parts that are lubricated by the oil.
Another area where a specially formulated air compressor oil is superior to a motor oil would be in its ability to reduce foaming. A high-quality air compressor oil will utilize a robust volume of heavy-duty antifoam agents. By reducing foam, you reduce high temperatures. By lowering temperatures, oil life is extended and wear is reduced.
In summary, air compressors require a lubricant specifically formulated and engineered for its unique operating design and operating conditions that a motor oil simply was not made to deal with.