Lubricant Low Temperature Pumpability Studies — Oil Formulation and Engine Hardware Effects 890037
Full scale vehicle pumpability testing has been conducted to define the effects of viscosity index improvers (VII's), pour depressants and basestocks on multigrade engine oil performance at low temperatures. Oils containing polymethacrylate VII's generally gave faster pressurization times than those with styrene-isoprene or olefin-copolymer additives. However, oils with all three VI improver types can be formulated to give satisfactory pressurization times. Basestocks with higher residual wax contents, used in combination with certain VII types were very sensitive to proper pour depressant selection, and some engine failures were observed with non-optimized mixtures.
Generally, SAE 0W30's gave more rapid lubrication than 5W30's, which in turn were better than 10W30's, although there were some exceptions to this order. Partial synthetic 0W30 and 5W30's could be formulated with performance approaching full synthetic lubricants.
Engine hardware effects were also investigated as part of this study. Although overhead cam gasoline engines were thought to be more severe in their pumpability requirement, some overhead valve designs appeared to be equally demanding of lubricant performance. Engine speed is a key operating parameter: oil pressurization times decreased by 30-50% by optimizing the fast idle speed of the engines.