It is necessary to consider the different viscosity-temperature performance as well as the different viscosity-pressure performance of traditional mineral oil based stern tube lubricants compared to EAL’s, to understand why EAL’s exhibit a new and different behaviour.
It is not recommendable to reduce the different behaviour of a broad variety of EAL base fluids to an EAL average which shall represent all kinds of base oil chemistry here. Note that saturated ester base performance is closest to mineral oil base performance characteristics, in terms of Viscosity Index, as well as in terms of Pressure-Viscosity Coefficient.
Base fluid properties are important but it is also necessary to observe the performance of the finished formulated fluid because additive chemistry can adversely affect base fluid physics under severe conditions due to chemical interactions of additives in the fluids. Viscosity Improvers and Emulsifiers can particularly affect a lubricant’s ability to perform as required and carry heat away from the bearings and seals, under adverse conditions of high pressure/shear stress and water contamination.
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