Wow! Certainly appreciate your replies and help. I’m certainly no expert, and that’s why I am posting here. From what research I have done, to find replacement parts, it seems that “that” particular thermostat riser and housing is only available on closed loop design.. Rall water thermostat riser looks quite different. Just wondering why if changing from raw water, to close loop, why someone would replace all the parts (riser, housing), etc. but keep the same thermostats, especially if they were fouled with sediment. Am I making any sense with that? Again, not to argue, but just debate and learn. Those are (I’m pretty sure) closed loop system thermostat housings, that are clogged up. Previous owner is stating that it was always closed loop, and the option sheet for that boat model has it as an option for that year. But, obviously I did not buy it new, so I would not know for sure. But again, raw water cooled housings look quite different. Was thinking “cheap” antifreeze could certainly have something to do with it, as well as perhaps using regular tap water. Anyway, I’m going through the whole thing, cleaning it out. The barnacle buster seems to be the way to go. Thank you again for your kind help and direction.
Norm