Identification of Mixed In-Service Automotive Fluids in CVT and Front Differential Using FTIR

A variety of petroleum-based fluids are used in modern internal combustion automobiles. These fluids have various characteristics based on the specific application and typically include engine oil, power steering fluid, automatic transmission fluid, etc. Transmission fluids can incorporate an array of additives that promote anti-wear, rust blocking and anti-corrosion such as dispersants, surfactants, viscosity index improvers etc. Gear oil used in the differentials work to lubricate and prevent corrosion and are generally much more viscous than transmission fluid. Accidental mixture (or substitution) of these fluids can compromise the intended function and lead to component and system failure. Post-failure forensic determination of the constituents of an accidental mixture is often needed to sort out the responsibilities and identification of fault related to the failure. Comparing subject fluids from a failed automobile to exemplar fluids using chemical analysis methods such as FTIR and EDS, as well as thermal analysis techniques such as TGA, provide data which is useful in assessing cross-contamination. This presentation expands on a case study involving a failure investigation that was conducted on a late model 2014 Subaru automobile that had stalled within two days after it received routine preventative maintenance service that involved a fluid flush of the drivetrain systems which included changing the continuously variable transmission (CVT) fluid in the CVT transmission and the gear oil in the differentials. Samples of the fluids taken from the drivetrain of the subject Subaru were analyzed and compared against new exemplar fluid using chemical analysis methods. Additionally, samples of various other manufacturer transmission fluids and gear oils were also obtained. Mixtures of various concentrations between the fluids were prepared and analyzed. The data from this analysis was conclusive in determining that there was cross-contamination between the CVT fluid and the gear oil, from the subject Subaru.