A novel technique for measuring very small variances in friction coeff
icient due to a change in oil or additive type (with particular emphas
is on hydraulic oils) is presented. A standard pin-on-disk tribometer
is used for test oil friction measurement in comparison with a referen
ce oil. The Oil Change Without Shutdown (OCWS) test procedure has been
used to increase test precision and eliminate the baseline variations
that are unavoidable with separate test measurements.