A repair shop that rebuilds and warrants automotive differentials asks about the capabilities of oil analysis.

A reader asks: Can oil analysis can pick out whether friction modifier additive has been added to gear oil in automotive differentials? We occasionally handle warranty claims on limited slip differential repair work. The biggest question is always whether or not friction modifier has been added to the gear oil. Can oil analysis determine whether limited slip differential additive has been added to the gear lube?

Our answer: We asked the Drive Train Product Specialist at Oil Analyzers Inc. for their thoughts on this question. Here’s their answer.

Unfortunately oil analysis would not be able to provide conclusive evidence of whether the proper amount of a friction modifier being used in a gear lube sample.

The presence of a friction modifier in a gear lube would not be indicated by a unique ingredient or chemical signature. Limited slip additives do contain a much higher level of phosphorous than the average gear lube. But the problem is that only a few ounces of friction modifier additive is used. So it would be impossible to determine whether the correct amount of additive was present in an oil sample. It becomes even more difficult once you begin to include various gear lubes and additives by different manufacturers. Also consider the residual amounts of previous lubricants and contaminants in the sample. When all of these factors are considered, oil analysis could not make a determination with any certainty.