It is possible to add Grainger part number 43Y891 synthetic motor oil with mineral oil. However, there are characteristics that are different; such as response to heat/cold temperatures and conditions. Also, how is this being added? Is this simply an effort to “top off” a level, or are you trying to create a different quality to the oil? Please consider calling Grainger to further discuss relevant details. The phone number is 1-800-323-0620.
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