Closed cooling means the engines are filled with antifreeze and therefor protected from the evils of winter assuming the antifreeze is up to spec. The only thing the raw water does is cool the antifreeze via a heat exchanger which basically replaces the radiator on a car. I also have closed cooling however different engines but it does remain the same procedure. Most simply unscrew the strainer cover and pour the pink stuff into her while the engine is started and run. I went a step further and machined a new strainer cap with a barb style hose fitting on the end so I use a 5 gallon pail of the ink stuff connected with a hose to my machined cap and fire her up. That is it for the engines.