While it seems like there should be tons of problems with these engines, there really don't seem to be that many problems. The YSM8 was a popular engine
and I have never run across problems with the system, maybe someone who has worked on them more than I can say whether they have seen problems. As long as the coolant
flow looks good, I wouldn't sweat it too much after asking around of people that work on the engines.
What boat is it in?