2. We have a 1972 Columbia 30 with a RWC A4 that was rebuilt in 1997 and is now overheating when at cruising speed (1700). I recently did an acid flush (as per your manual), but the engine still overheats, though not as much as prior to the flush. During the flush, it took about 5 minutes to empty the acid bucket which would indicate blockages in the cooling passages (impeller and thermostat are fine). How do I go about manually cleaning the passages that I can access without removing and stripping the engine down to have everything chemically cleaned out?

If I'm doing the math correctly, you're only able to pump one gallon per minute through your cooling system. In most cases, blockages of this magnitude are not the result of general clogging of cooling jackets, but rather serious localized restrictions within a fitting.

Since you're experiencing a restriction to total flow, I would remove the hose to the inlet of your thermostat housing (directly above the starter) and run the engine for a few seconds. If you have good flow there, reconnect the hose and remove the one from behind the manifold and run the engine for a few more seconds. If you have good flow there, reconnect the hose and remove the end of the hose that connects to the exhaust system and run the engine again. By this process, you should be able to identify the segment of your system that is blocked, and limit the fittings to check. - Updated: January 3, 2004