Kyle, close your raw water intake, remove end plates on exchanger (maybe a gallon of water?). determine where you wish to unhook and drain engine coolant(approx 2 gallons). at this point you probably have to remove the transmission cooler to remove the 2 bolts holding the main heat exchanger. As long as you have two coolers off you might as well take off the oil cooler as well, and open your raw water pump and check/ change impeller. Inspect all three heat exchangers, clean, replace, boil out as needed, replace hoses as needed, etc. Also if you have the old stye 2 piece raw water pump and many engine hours you might think of inspecting the wear of the drive tangs...four bolts holding the two halves together. If they are worn you need to replace the pump, approx $500 from American diesel
One more thing to do is replace the thermostat under the expansion tank as you now have the entire engine cooling system torn apart. See how simple that is?
I just did all this about a month ago so now Im good for a while.
The other choice would be to do this in the fall when you are ready to put the boat away rather than now when you probably would rather be boating
. If you are worried about your heat exchanger you can inspect and flush it without having to remove it from the boat. Simply remove the plates on both ends and clean, flush rod out with soft dowel,etc, after making sure your seacock is closed. Hope this helps,