I recently removed the heat exchangers from my twin 502's and want to flush and fill the system. Closed cooling of course. I have looked at many diagrams to find a drain plug on the block but the older Mercruiser guides I've looked at haven't been much help and I cannot seem to find on the block. The only thing I can think of is pull a hose, start the engine and put a hose in the exchange and will with water until all the fluid is in the bilge. If anyone has a diagram I can look at to show the plugs and their location, I'd prefer to do it that way.
PS knowing what I know about this boat, I suspect the fluid has been in there for 20 years which is why I am eager to change.