OK so i had a seawater pump impellor fail on me. A piece of plastic broke on the housing and shredded the impellor. I replaced everything but now when I start the boat I notce more water coming out the driver side exhaust. I let it run for a while at idle and the exhaust manifold on that side is much hotter than the other. I turn off the engine ,enough for that day.. OK A week later I start the boat again and now more water is coming from the pass side exhaust.Now that exhaust manifold is getting hotter.So here is what I do. While idling I disconnect each hose one at a time where they jion at the thermostat housing. Water seems to be flowing fine. I never drove the boat but each time I let the boat warm to 155 degrees on the gauge. Whats up???????

Sounds like you have a piece of your impeller bouncing around in there. I would try using a garden hose and back flush everything including your oil cooler.

You might have a small piece of impeller moving around and getting stuck in the top of the brass T fitting on top of the Tsat housing. The brass T has a check ball type mechanism to help distribute flow evenly to both sides of the exhaust.

Parts 4-8 in the linked pic.
http://www.mercruiserparts.com/Show_...MOSTAT+HOUSING

Mine is not a closed cooling system. Is it the same check ball on an open system?

Yep, same thing. My 525SC was exactly the same and no closed cooling.