I can't help you with your core removal as my engines are 8v53's . However i do have a story about cleaning them yourself . I bought my 41C seven years ago and one of the first things i did was to pull and clean the heat exchangers. Good thing to, the two inch inlets and outlets were down to about 3/4 of an inch! After reading about cleaning them yourself by dipping them in muriatic acid thats what i did. They came out brite and shinny as new. Two years later i decided to pull and check them agan so i could get an idea about future cleaning intervals. They were in pretty good shape, so i dipped them in acid again ( mine fit perfectly into a five gallon bucket ) ,neutralized them with baking soda and reinstalled them. Two mounths later while doing my prestart checks i found zero water in the starbord engines holding tank!! All the implications seemed bad, blown head , lost season, lots of lost money. So for the first and so far only time i called in a pro. His first check was to put a pressure gage on the radiator cap. The tank pressure was way high. He said the heat exchanger was clogged, no way i just did them! He convinced me that it was the the logical place to start.So i told him to have at it. I thought this was just the first spin of the big money wheel. Well, he was wright, it seems muriatic acid only cleans the salt water side and does nothing for the fresh water stde. those tubes were totally blocked. That was a $400.00 lesson learned. Take them to a radiator shop and let them boil them in their solution. I pay $75.00 each and now they really do come out brite and shinny as new.
