I had an in frame of all six holes done a few years back, since then I have experienced a overheating issue @ 2100 or above. I am hearing that since I used the (at the time) new ceramic kits from DD, that the ceramics hold too much heat, not allowing for the engineered exchange. The only sinificant difference on that rebuild was no "dog bone" heads were available, so a Cast Tech,remanufactured standard DD head was used. My exchange was stated to have the "starburst" Cracks, making it NG for the rebuild. This mech. who did rebuild says the engine needed break in time. I have put about 22 hrs on it, as the boat only gets modest use. I found no suspects in the cooling system. of course the wrench has disappeared! Thanks