merecruis 4.3 gm heat echanger

[mike reese]

i have a merecriuse 4.3 175 hp need some advice
ran good a couple times the last time all 6 cyl filled with water
never hot not headgasket im sure its the heat exchanger but am not sure how they work
is there a one way valve that lets exhaust out no water in or is there two different chambers that do not meet
also i should add it is a freshwater boat
seem to me when i shut off motor after driving fine all 6 cyl filled almost immediatley with lake water

 

[Docksidemarineservices]

It is not the heat exchanger. How old are the manifolds and risers? More than 5 years is my guess. Time for new exhaust.