Hey ThanksDear @Shagdance ,
Good afternoon! We use it here at work all the time to clean raw water exchanges. Just make sure you have a way to flush the system with Barnacle Buster with enough pressure. Also be sure to run a secondary flush with fresh water to clean out any remaining Barnacle Buster. Hope this helps!
Heat exchanger is better to be removed and serviced by a radiator shop. The will clean all the tubes and then pressure test the unit to make sure all is operational.try same thing
with my Yanmar heat exchanger.