Overheating Issue

I just did a 3412, in dropped an entire intake valve seat. The boat sat a lot. Tore up the turbo pretty good, but the cylinder and piston were perfect. Sometimes you get lucky.....but usually not.

I too would pull the other head and have it done......sitting does them no favors.

Detroits ?
Original cast iron heat exchangers ?
HP ?

Mt friend's 692, 550 HP, cast irons units where ultra-sonically cleaned which solved his problem.
I replaced mine with Lenco's . I have 671's - 410 hp

You probably have sea skank in the tank! and else where...
I use Barnacle Buster, two gallons and mix with two gallons of water and run that through my 471's let it soak for 6/8 hours. Hook back up the sea water hose and open up the sea cock and run the engine for a bit. Watch the junk come out of the exhaust when you first start it up. You'll be amazed. It cleans out the heat exchanger and all of the sea water system with in the engine.
That cured my engine, running hot at 185/190 2000 rpm, now 175 at 2000 rpm.

I'm sure stuff grows quickly in that warm Gulf water , which also grows in the engine. Unless you run 5/7 days a week, crap will grow/form with in.

I thought Sen-dure was the only heat exchanger made for Detroits, J & T etc. ?

Not necessarily you generally have to treat each engine independently in my opinion .
when you say cast the only thing that cast is the holding tank for the antifreeze and the heat exchanger ,the heat exchanger which is a rectangle shaped unit is bronze and has a bunch a little teeny tubes running through it and holes that’s the thing they can get clogged up easily even after one year with sea growth .

You only have to remove one side, I think it’s the inlet side, anyway it’s the side with the flange on the Sun-dure heat exchanger, then slide it out with some effort ...
It’s more than moving just the tubes, there are end caps etc that have to be moved also.
Make sure you get new gaskets for the reinstall, don’t cheat with RTV crap. Also you will need to install a new big rubber o- ring that is in there too.
I get it all from J&T Mt Laurel Nj.

Anyway, I would still do the barnacle buster treatment first .
There is other stuff out there on the market to buy a different name but it does the same thing .

In my case only the Port engine would run hot. Starboard ran right at temp.

I can't answer that. All I can tell you id Lenco makes a HE for my engines. They make all kinds of HE's , oil, trans etc.
Maybe Sen-dure made the cast ones ?
The Lencos are not cast, more cooling capacity but do not last as long as the cast ones.

I think I figured it out, mine are J and T cast tank, not the Cylinder tube type that both Lenco and Sen-dure make. I thought all Detroits had a big ass heavy cast tank on the front of them to which the heat exchanger was in. I believe J and T made there own tank to which the big bronze rectangle HE was used.
I think we need Capt Ralph to chime in and unravel the mess I have created! Lol

I had an overheat problem many years ago that turned out to be the cast iron mixing elbows you call " dump cans " ? They were almost totally clogged w rust.
Went through two pair over the years before getting stainless steel ones from DeAngelo.

Are the exhaust mixing elbows stainless steel and look new or are they the old cast-iron ones ?
Just like Chesapeake 46 described .

I replaced one of mine two years ago got it from J&T they only come stainless steel now no more cast-iron elbows are made .

In my opinion stop guessing / over thinking and run some barnacle buster or whatever through the engine first and then go from there ....
$60 a gallon jug.
Get the engine warm first so all and any thermostats are opened up so you get that stuff throughout the engine and let her soak, see what happens .