454 with thru hull exhaust...

I changed my sea water pump on Friday, all the fins tore off and went downstream. I flushed water back through the system from the supply line to the thermostat and saw some pieces wash out into the bilge.

Last night the 2" line that goes between the thermostat housing and the circulation pump burst. I changed that line, and test fired the motor. After a minute or so, water started spraying out of the circulation pump and the big 2" started to swell.

I pulled the thermostat housing and circulation pumps off and I don't see any blockage in either one. I also dumped water into the top of the block to make sure it would run out of the ports on the front - which it does.

I can blow through the water lines that go to the exhaust, but it takes some effort. My best guess is that the exhaust elbows are partially blocked? I'm not sure what else could be causing it.

Generally any big pieces will get stuck at the front of the oil cooler. Pull the hoses on the oil cooler and feel inside and backflush it.

Okay, I'll pull those lines off and double check. If the impeller chunks didn't cause a blockage downstream of that 2" t-stat line, I don't know what's causing my problem.

What else could be causing the excess pressure?
Does all of the water flow through the exhaust elbows and out the exhaust before the thermostat opens?

Just trying figure out a way to definitively know its a clog in the exhaust elbows before I open that can of worms. The bolts are most definitely going to require O2 & acetylene to remove.

YES.

Every drop has to exit the exhaust. They could be corroded closed, or have chunks in there.

On thing is for sure, if you are using a torch to get them apart, you'll be replacing manifolds AND risers. Probably not a bad idea if they are that nasty on the outside.

Actually, they look great on the outside... its just the bolts that look like ****.

And to clarify my question... I know all the water goes out the exhaust, I just wanted to make sure it all flows through the elbows only until the thermostat opens and then it flows through the manifolds.... I drew that conclusion from inspecting the tstat housing and was just looking for confirmation.

Thanks for the help.