The driving comfort and safety of electric vehicles depend significantly on the performance, lifetime, and functionality of wet clutches serving as a subsystem of the power transmission in the drivetrain. As part of the project, changes in transmission oil properties due to the contamination of water and iron particles, which are introduced into the oil by environmental influences or the wear of various machine components, are being investigated. This performance loss is evaluated through the tribological changes in the friction behavior of wet clutches. ICP analyses have shown that, among all the elements produced by wear, iron in particular leads to a deterioration in oil performance. To specifically investigate this influence, experiments with artificially added iron powder as well as with pre-damaged oils are conducted, and the interaction with water addition is analyzed. This allows for a targeted investigation of the influence of iron particles, independent of the energy introduced into the system. The performance degradation of the transmission oil is correlated with the gradient of the coefficient of friction over the sliding speed, along with the water and iron content as well as the mechanical energy input into the transmission oil.