Re: losing. antifreeze not leaking
heat exchanger leaking internally mixing the A/F with the seawater
Could be, drain a little of the fresh water out of the exchanger (aft plug) and see if antifreeze there. Pull the plugs, check the porcelain tips. Should be tan or brown, if white you are getting coolant leaking past head gasket into combustion chamber. Do a compression test and a cooling system test, free loner tools for both from Autozone. Only other place, leaking exhaust riser. Check the water pump weep hole (lower starboard side of engine water pump) for coolant leak while running. Good luck.
