Freshwater cooling system for Large High Rise Mercruiser 225/228/305/350 Chevrolet marine engine. Kit includes: heat exchanger, mounts, gaskets, thermostat, thermostat housing, hoses, hose clamps, hose fittings, & fasteners. Cools block & manifolds. Model 255 needs to have power steering pump that is mounted on the port cylinder head relocated for kit to fit. Exhaust manifolds must have casting number 47737 and 47738 (or an exact replacement).