Two Oils Both “Meet the Specification”—So Why Can Mixing Them Cause Problems in the System?

Lubricant Compatibility is a matter of Chemistry, not simply Viscosity Grade or OEM Specification.

Technical Explanation

Lubricant Compatibility covers more than Base Oil compatibility. Finished Lubricants contain Antioxidants, Rust Inhibitors, Anti-foam, Demulsifiers, and other Additives balanced into the formulation. When two formulations are mixed, reactions or Additive imbalance can cause Haze, Precipitation, Foaming, or Performance Shift.

Residual Oil in the Cooler, Piping, Bearing Housing, and Low Points means the system almost never changes completely from Formula A to Formula B in a single step. The Mix Ratio during the Transition is therefore important.

Compatibility Testing before Conversion typically evaluates multiple blend ratios and observes Physical/Chemical Stability for the intended purpose. However, Lab results cannot fully replace Drain/Rinse planning and post-Start-up monitoring.

In addition to Oil-Oil Compatibility, Seal, Coating, and Material Compatibility should also be considered when changing Chemistry significantly.

Impact on Equipment

Additive Dropout or Deposits after Oil Conversion.
Changes in Foaming/Air Release or Water Separability.
Filter Plugging after adding new oil.
Early Oil Analysis results are difficult to interpret because multiple formulations are mixed.
New Oil Performance is not fully represented because Residual Oil remains at a high level.

Recommended Approach

Before Conversion, determine System Volume, Drainable Volume, and Residual Estimate, and conduct Compatibility Testing according to the risk level. Then choose whether to Drain & Fill, Rinse, or perform additional Cleaning based on the system condition rather than applying one procedure to every machine.

After Start-up, establish a new Baseline and monitor Appearance, Foaming, Water Separation, Filter DP, and Oil Analysis more frequently than normal during the initial period.

What Can SUTAIYO & Lubefix Do?SUTAIYO can develop a Conversion Plan when customers need to move to Mobil Lubricants, considering Compatibility, Residual Oil, and Operating Requirements before the actual change.Lubefix can handle Drain, Rinse, Filtration, and Filling in the field so the Transition is controlled and the customer does not have to coordinate multiple parties separately.

Expected Customer Outcomes• Reduce the risk of Deposits and Performance Shift after an oil change.• Help the new Mobil Lubricant begin operating closer to its Designed Performance.• Reduce the complexity of Oil Conversion and Start-up Monitoring.