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Biodiesel is a biodegradable fuel that consists of alkyl esters, obtained from renewable sources, vegetal oil and animal fats reacting with a short-chain of aliphatic alcohols (typically methanol or ethanol) in the presence of a catalyst (reaction known as transesterification). An important property to use the biodiesel as fuel in diesel engines is its oxidation stability because biodiesel can contain unsaturated fatty acids, which are susceptible to oxidation, being able to change into polymerized compounds, which can cause engine problems such as blocked fuel filters. Numerous analytical methods have been applied to determine oxidation stability, European Union and Brazil use the same method DIN EN 14112 - known as Rancimat method that consists in the sample heating to 110°C where the products formed by the decomposition are blown inside by a flow of air in to measurement cell with distilled water.

The used oils in diferencial of commercial vehicles, of type SAE 90 API GL-5, under extreme conditions of work for which the diferencial was not projected for example (highways with bad conservation, load excess, axis not adapted for certain uses, etc.) degrades disabling the identification of the oil type (formulation) applied hindering the correct evaluation of a warranty process originally or of technical attendance. The tracer addition (it nourishes organometalica) to the oil of diferencial finish since it is stable to extreme conditions of work, it can indicate the type of used oil as well as its formulation. The study of the stability of the tracer in the oil is made using the apparel of 4 spheres, in which the property antidesgaste of the package is evaluated through a forced rehearsal of degradation of the oil the waste of the cap of the sphere, the rugosidade and the temperature generated during the rehearsal being measured.