Abstract: A device and a method for the modification of an operating all-loss engine lubricant's properties in response to actual engine operating conditions. The present invention is a method that comprises (1) monitoring the specific engine parameter(s) of interest, or in the alternative, predicting those parameter(s) from other engine inputs for a crosshead diesel engine; (2) calculating from said parameter(s) or input(s) the amount of performance enhancer(s), base lubricant or alternatively formulated lubricant that need be added to the engine's base lubricant; and (3) modifying said base lubricant with said performance enhancers, additional base lubricant or alternatively formulated lubricant before introduction the combination into said monitored part or location.