River boat heat exchanger

[fish4kok]

I just got 1991 20' Custom-Weld river boat in January, it has a close loop cooling system. Last week when I winterize and test the old antifreeze in the engine. the result it was mixed for about +5 degree, the antifreeze level was low so I drained all coolant (engine and heater core) and filled up with 50/50 mixed (-35deg F). I took the boat out to LP to run test the engine and top off the antifreeze. After ran the engine for awhile then the antifreeze in the heat exchange drop down too. I'm not sure because air in the system caused it drop or it might leak in the heat exchanger or head gasket cracked (Haven't check the engine oil). I didn't see any antifreeze leak in the boat. I'll run test the engine again.
What is the normal level of the antifreeze in the heat exchanger?
What is the best method to test the heat exchanger, how much pressure to apply?
It would be greatly appreciated for your answer.

[fish4kok]

Today, I open the end cap of heat exchanger and found antifreeze in the bottom where is raw water chamber entrance . So the heat exchanger has bad tube. There are many tubes and I don't know how many of them split . I call King radiator and they told me take to their shop they can test and repair. I took it out of the engine and leaned it on the corner of the boat. Bad part was when I reached it from outside of the boat and raised above the hand rail, somehow that heat xchanger slipped off my hand and landed on the drive way with the end cap down, it's damaged very bad. It's repairable but may be expensive.
Anyway I took to the shop and asked them pressure test to find how many tubes are bad and quote for the total repair. He has not call me back yet.
Other bad new is the Red Line who manufacture for that engine was out of business so no replacement part.
That will be an expensive repair.