Abstract: A fresh water flushing system for a marine engine in a boat for use whether the boat is in or out of the water is disclosed. The system comprises a control panel mounted on the interior of the boat, a plurality of tubular "T" shaped interconnection fittings in a raw sea water cooling conduit, and a fresh water flush valve therebetween. The components are connected for fresh water fluid flow with a plurality of standard radiator hoses. The fresh water flush valve has a valve plunger for establishing fresh water flow between the control panel and the "T" shaped interconnection fittings. Further, the fresh water flush valve has a plurality of axial outlet ports to proportionately direct the flow of fresh water to the appropriate "T" shaped interconnection fitting in the raw sea water cooling conduit of the marine engine. A valve plug is provided to secure a positive closure when the fresh water flow is disconnected.