CUSCO 965 051 A Reserve tank for TOYOTA GT86, SUBARU BRZThe water pump on an engine is constantly being driven and is all relative to the crankshaft revolution. During a more aggressive maneuver typically at the higher RPM region, the water is circulated with more flow. This circulation is at times too strong that it becomes prone to bubbling which then leads to cavitation. The final effect of this occurence is that the cooling efficiency of the engine suffers from within the water jacket passages,