Why Oils Should Not Be Mixed

Noria Corporation
Tags: hydraulics, oil analysis, contamination control

"Is it all right to mix an R&O hydraulic oil with an AW hydraulic oil in a hydraulic application?"

Mixing oils with different additive packages is never recommended. Doing so could compromise the additive performance of both constituents, cause corrosion of component surfaces and lead to increased mechanical wear. Trending of some oil analysis properties also will be compromised.

In a pinch, if the oils are the same viscosity, you may be able to get away with mixing for a short time. If you must mix the oils or live with an accidental mixture until the next scheduled outage, take the following precautions:

  1. Visually inspect for signs of sludge, poor demulsibility and foaming.

  2. Increase the frequency of oil analysis to spot abnormal wear, corrosion or lubricant degradation.

  3. Flush and change the oil as quickly as possible. A drain leaves 5 to 40 percent of the old oil in the system. Therefore, a flush will need to be performed.

  4. Keep up the frequent inspections and oil analysis to be sure that the oil stabilizes.