Ayuh,... If yer boatin' in Brine, freshwater coolin' is most always a good idea,...
But,...
After 5 Years of Brine, it's too late, it's salt soaked, 'n will react with the antifreeze,...
Run 'er til she rots out, 'n then worry 'bout freshwater coolin',...
So is Yer motor cast iron or aluminum,..?? A magnet will tell ya,...