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Flouroelastomers and silicone rubbers are commonly employed in static and dynamic seals for automotive applications. In order to prevent premature failures and leakages caused by swelling and/or changes in their mechanical properties, materials for seals are selected according to their compatibility with the environment and fluids involved in the engine operation. Thus, in particular, the use of new fuels and additives in automotive engines requires the assessment of compatibility with common sealing elastomers to prevent failures. Currently, Jatropha oil is being used as a renewable source of fuel in diesel engines for electricity production, transport or agricultural mechanization in various countries. It is used either as biodiesel or as straight vegetable oil (SVO) since it has good heating power and provide exhaust gas with almost no sulfur or aromatic polycyclic compounds. However, the compatibility of elastomers with this SVO has not been investigated yet.

It has widely reported that tribological performance of engine mineral oils (EMOs) can be improved by blending them with vegetable oils (VOs) in certain concentrations. Nonetheless, bio-oils are more susceptible to oxidation than EMOs by thermal ageing, which could be a drawback when they are used in engines comprising high variations of temperature. In this paper, a comparative analysis of tribological performance of an EMO and a blend made of 80%vol. of EMO and 20%vol. of a VO in fresh and aged conditions is given. The VO selected for the blend was Jatropha oil since various advantages reported in literature. EMO and B20 were thermally aged in laboratory approaching actual oxidation and additives depletion caused in EMO used in a car for 7500 km. The effects of ageing on the oils were evaluated by means of oxidation (PAI value), Zinc dialkyldithiophosphates (ZDDPs) depletion and viscosity.