Well, I limped her through Labor Day Weekend with an underlying overheating problem. To me more specific, a warm running condition. Subject vessel is a 1972 '41 Commander with mighty 427s and closed cooling. I won't go into the details about how the broker flat out lied about most aspects of the pre-purchase maintenance performed. Instead, I will present every reason not to believe that any serviceable system has been serviced by the book. Bubba did new impellers so, up to this weekend I hung my hat on the notion that the raw water system was not the cause of my heating issues. However, I also know to start with the basics, so my attention went back to the foundation of any boat engine's cooling system: raw water flow.
Consulting this trusty forum, I ordered up the correct Sherwood impeller and cam plate for each engine. Now I cant remember who here said doing the impeller alone is only half the job, but boy were they right in my situation. I forgot to grab pictures of the impellers, but basically the abraded cam plates shredded the tips of the new impellers.
The worn cam was also thinner than the new one. In summary, the total pump flow curve was way off and not pumping enough water. After rebuilding the pumps, back flushing from the HX outlet backwards to the raw water pump outlet, flushing both paths to the risers, checking PRV function and cleaning the strainer both engines went from idling at 180F to 165F.
Now, my starboard engine still runs warmer than I like at power, but I'll start a separate thread to discuss. The moral of my story is do the COMPLETE job, and do it yourself, because nobody cares more about your boat than you!
Good job on fixing the raw water pump correctly . The brass wear plate is the most overlooked item when an impellor is replaced . The wear plate # 10944 for that Sherwood pump when new is a nominal .196 thick at the center radius .
Just think how many raw water pumps have not been serviced correctly over decades of wear !