Get some radiator flush follow directions.drain the system by opening the draincock on the bottom of the radiator and the one on the side of the block(may have a plug in the place where a draincock can go). There should be one on each side of a V-type engine,but on your 235 it will be on the driver-side toward the rear of the engine.(you can install draincocks in the place you removed the plugs).
Put in some radiator sealer/conditioner and add 50/50 mix of antifreeze/water.
