Investigation of the Effects of Mixtures of Dissimilar Engine Coolant Inhibitor Chemistries on Automotive Water Pump Durability

摘要

Modem aftermarket water pumps are engineered to provide at least 100 000 miles of service. Most of these pumps are manufactured with aluminum alloys with cast aluminum cases being particularly common. Other pump components may contain cast or extruded aluminum, cast iron, stamped steel, or plastic. Failures of aftermarket water pumps are typically indicated by excessive coolant loss through the weep hole. An investigation into the root cause of the failures was conducted. Areas of focus for determining the root cause of premature failures included investigations of various destructive mechanisms including physical erosion and evaluations of the corrosion behavior of new, unconditioned metals in the water pumps. Of particular interest was the possibility of corrosion when parts are exposed to engine coolant solutions that contain mixtures of North American factory-fill coolants. All of the North American original equipment manufacturers (OEMs) recommend against mixing coolants, but no data concerning the effects of mixing could be found. Nevertheless, consumer or installer mixing of dissimilar coolant formulations is common, because many coolant formulations are marketed for use in "All Makes, All Models" of vehicles and/or are labeled "Mixes with Any Color Antifreeze." It is assumed that these claims are well researched and are for top-off applications. However, the target of this investigation is the capability of coolant mixtures to protect previously unpassivated metals, especially those in aftermarket water pumps. For this research, four common but dissimilar OEM factory-fill coolant formulations were obtained. Coolants were mixed with each other and the ASTM "Water Pump, Corrosion in Glassware," and "Corrosion of Heat Rejecting Aluminum Surfaces" test methods were used to learn what the effects of the coolant mixtures are. This paper reports the results of those tests and provides support for a position by the water pump supplier that dissimilar coolant formulations should not be mixed when new cooling system components are installed. It also provides data for ASTM Committee D15 on Engine Coolants and Related Fluids to consider in possibly drafting a coolant compatibility standard.