FILTERS of various types were tested with nonadditive mineral and two heavy-duty oils containing additives similar to the extreme types commercially available.
In many cases the efficiency of a filter varied considerably, depending on the oil used. For instance, the efficiency of some filters with one additive oil was about the same as with the straight mineral oil but was much lower with the other type of additive oil. One filter had about the same efficiency with the nonadditive oil and with both of the additive oils.
