Installed a full closed cooled system on a 300 horse 350. Block runs at 170, manifolds are cooled after antifreeze leaves the block and they are running about 215. Sea water temp is 60 and water leaving through risers is at 110.
How do these numbers sound? Manifolds seem hot but the incoming cooling fluid is already at 170 and the exhaust puts out a lot of heat so the 40 degree increase may be normal

What temp stat you using

I believe its a 165

is your raw pump in good shape if so put a 140 stat in and see what your temps are takes a lot to cool the exhaust manifolds off with a closed system

Are the manifolds anything special? If standard merc wet joint center dumps, you might wanna run the whole exhaust raw water. Especially as sealing that wet joint so raw on 1 side and antifreeze on the other is a pain. I gave up on running antifreeze in the manifolds in my sportfish-summer house and life is easier.

They are aluminum glms, basically brand new.

my question was really was if anyone with a closed cooled system has shot their manifolds with a temp gun under load. I know if the cooling fluid is coming into the manifold at 170 it will leave quite a bit hotter, just not sure how much. The engine maintains 170 no problem.

Will probably switch to a 145 thermostat to lower the incoming temp to the manifolds.