Mercury - Quicksilver Distributor Cap Kit For Marinized GM V8 MerCruiser Engines with Thunderbolt IV & V 805759Q3. Overview. If your V8 MerCruiser has been running a little rough or struggling to start, it might be time to refresh the ignition system. The Mercury Marine 805759Q3 Quicksilver Distributor Cap Kit makes it easy to get your spark back where it belongs. This kit includes the cap, rotor, and gasket - all built to factory specs for GM-based MerCruiser engines running Thunderbolt IV or V