I have currently drained both power-plants and removed inspection covers, end caps. Port side is pretty clean, only a small amount of scale that has apparently sluffed off tube bundle collected on bottom inspection covers. I'm just pressure washing the insides and and putting it back together with fresh coolant. The starboard side is a different story, when I purchased the boat over a year ago the coolant was pretty muddy on starboard, I flushed substantially last fall until all I got was clean water and refilled with new coolant. Sometime in the spring this power-plant started seeping coolant at most inspection covers, coolant has stayed clean all year though. None the less it was time to do some tear down, when I removed the end caps it became apparent that the bundle had leaked salt water into coolant at some point in timeline prior to my ownership. Someone has "repaired" the bundle by screwing some machine screws in either end of a tube and sealing with some hard white substance. It is apparent that it ran prior to the repair for some time due to a substantial amount of hard white taburcle growth on most internal coolant passages. My question to the group regards what my best options are to "clean" the engine coolant passages? I have removed the manicooler and will scrub it out and have the bundle assessed by a radiator shop. I'm not sure I'm going to go for ceramic coating, there is virtually no pitting or material erosion on either manicooler. With regular inspections, maintenance and coolant changes I can't imagine these that are already 30 years old will not last another 20 easily.
"My question to the group regards what my best options are to "clean" the engine coolant passages?"
If you feel you need a flush in addition to the steps you are taking utilize any aluminum safe car/truck flushing agent in the recommended ratios for that flush. Since your boats coolant system holds more (about 25 qts) than twice the capacity of a typical trucks system you will need more than one bottle' per engine for flushing.
Please do a great job of rinsing out the flushing agent after use with at least two good rounds of a water rinse cold to hot engine as the flushing instructions will instruct.
Jim: Thanks for the info re the shop in Rancho Cucamonga. I think I met you at the Isthmus a few years ago. I have a 38 with a hardtop over the cockpit and green canvas. Bare Necessities. Hope to see you next summer. Where did you get your gaskets and O rings?