Mercury - Circulating Pump Cooling System Component Precision Marine Build 8M0116534. Overview. Anyone who runs a MerCruiser engine knows that a smooth-running cooling system is the heartbeat of a good boating day. When your engine temperature stays steady, everything else feels easier-whether you're easing into a quiet cove or pushing across open water with friends onboard. The Mercury 8M0116534 Circulating Pump is one of those components you rarely think about until it reminds you how importan