Group II


base oil migration in hydraulic oil formulations


Oxidation has been the enemy of hydraulic oils since their inception, arising from various sources including thermoxidative- degradation, wear metal ingress, air entrainment and a plethora of possible contaminants arising from its use. The goal of the formulator is to delay, pacify, prevent or disrupt these processes, enabling prolonged lubrication under all operating regimes the fluid was originally designed for. Whilst various additives can address the fundamental principles of oxidation, the underlying fact is that >90% of the formulation is solely a hydrocarbon source and therefore the selection of base fluid has become ever more critical to meet the demands of modern hydraulic systems, with ever increasing demands for prolonged drain times.


the mere 1:1 substitution over previously optimised formulations on Group I does not necessarily produce a better hydraulic fluid. The higher levels of sulphur in Group I base oils are, by design themselves, oxidation inhibitors before considering the impact of higher saturation on solubility. The graphs below summarise the increased oxidative stability when switching to Group II base stocks and, whilst the selection of base stocks within Grouping can be further explored, it is not the intention of this report to compare base sources within groups but to highlight the general trend in oxidative performance.


Changes to PCMO and HDEO engine oils over the last decade have made Group II base oils more accessible and therefore they have naturally found their way into industrial applications. But


Data based upon fully formulated fluids.


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LUBE MAGAZINE NO.127 JUNE 2015


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