Created with Sketch. Created with Sketch.
Why You Need To Understand MIL SPEC Oil Compatibility Before Purchasing Your Lubricants

Why You Need To Understand MIL SPEC Oil Compatibility Before Purchasing Your Lubricants

Jul 19th 2021

Thousands of maintenance crews across the United States top off or refill their equipment with industrial lubricants as part of their morning maintenance routine. There may be no ill-motive, with the intention being to preserve, protect and lubricate their machine surfaces. Unknown to them, they may mistakenly add two incompatible oils to their plant machinery.

Causes Of Lubricant Incompatibility

Most manufacturers have little knowledge of the type of cutting fluids, oils, and lubricants used on their machines. An Edelman Intelligence survey showed that only 42% of firms had the correct lubrication protocols in place. 63% of respondents did not offer any training to their staff on oils and lubricants. As such, the inadvertent mixing of incompatible mixing of oils is quite common. Other causes of lubricant incompatibility include:

  • Change of lubricant oil distributor
  • A shift in machine application or reliability requirements necessitating an oil change
  • New or remanufactured machines shipped with unknown oil solutions or corrosion preservatives in their internal surfaces
  • Practical inability to drain all previously incompatible lubricant
  • Failure to follow instructions such as MIL SPEC Oil Compatibility guidelines present on the containers.

Dangers Of Lubricant Incompatibility

Even world-class maintenance crews face cases of oil incompatibility from time to time. Mixing of different lubricants with varying properties and additives may lead to an adverse reaction of the two oils in a system. More often, the incompatibility arises from the neutralization of the acidic components of one oil type by the alkaline additives of another. The incompatibility may lead to corrosion, machine damage, acid formations, and oil carbonization.

MIL SPEC Oil Compatibility

The US Department of Defense Maintains a wide range of equipment, vehicles, and crafts that require different oils and fluids for proper operation. To counter issues arising from unintentional mixing of incompatible lubricants, the DoD came up with unique military specifications, commonly referred to as MIL SPEC or MIL-STD.

The performance specifications of the MIL SPEC oil compatibility provide a threshold for the functional requirements and specific properties of the lubricants to use in military equipment. However, the MIL SPEC lubricants and oils are used in a variety of ways outside the military, with certain commercial and industrial applications adopting the standards.

MIL SPEC Oil Compatibility Testing

Fluids, oils, or lubricants that can be mixed without any reaction may be deemed compatible. Semi-synthetic lubricants often contain less than 30% of oil content in concentrate while pure synthetics contain no oil whatsoever. You may need to verify the properties of the oil from the manufacturer’s MIL SPEC guidelines of the label.

The individual MIL SPEC Oil standards may include requirements for assuring compatibility of like or similar fluids. There are many procedures accepted as measures for determining lubricant compatibility including Method 3470.1 on Homegeniety and Miscibility of Oils, Method 3420.2 on Compatibility Characteristics of Universe Gear Lubricants, Method 3440.1 on Storage Stability Characteristics of Universal Gear Lubricants among many others. These procedures can be adapted or modified to fit your operational requirements.


Lubricant incompatibility can cause significant issues in the operation of your equipment. Following MIL SPEC oil compatibility guidelines can help prevent the inadvertent mixing of incompatible oils. To place an order for MIL SPEC Oil Lubricants, reach out to Santie Oil Company.