Freshwater cooling coversion and 3" spacer block water flow passages

Raytard

New Member
Mar 30, 2015
17
Alberta
Boat Info
97 Sea Ray 270 Sundancer
2006 Crown Trailer
08 Dodge 2500 deleted 6.7
Engines
7.4 merc bravo 1
Hi there, I am doing a raw water to FULL fresh water cooling conversion on a 7.4LX. I have seen in the Mercury bulletins that they recommend putting the block off gasket between the manifold and the spacer. And not between the spacer and elbow? I was hoping to put the block off gasket on top so the spacer would also see antifreeze and be protected better.
Anyways, my main question is, how does the spacer get cooling all around its four ports when a block-off gasket is installed? It seems that the plug on the spacer is only connected to one port. I am pretty sure from having them apart last season that each passage is not connected to each other on the spacer right? If that's the case, then only one port will see coolant (or raw water depending on where I put the gasket).
What am I missing, is there certain spacers specific to fresh water systems only?

Thank you for your replies, so far I've found the Mc324 kit for around $1050 and up. Add manifolds, spacers, bellows kit and a steering pin overhaul kit, and my Canadian wallet is going to take a big hit:smt119
 
Do you have carb or MPI if MPI you will need to change computer or get it reprogramed by a speed shop in northern calf. On a 19 year old boat it is a waste of money to even think about save your money for a new gm 454.
 
Sorry what? I have throttle body efi, not Mpi. What would be the difference if I plan on running the engine at the same temperature.
 
Sorry what? I have throttle body efi, not Mpi. What would be the difference if I plan on running the engine at the same temperature.

The Engine is not going to run at the same temperature as a raw water cooled one.
A FWC runs Hotter and at a consistent temperature .
 
Ok, I see were this is coming from. So maybe 10 degrees more? I run 170 most of the time so I will take my chances.
Back on track, can any one enlighten me on how a standard 3" exhaust spacer gets full surrounded cooling in all 4 ports when a block off gasket is used on either the top or bottom ?
 
It is a function of where you install pipe barbs and hoses. With blocking on bottom.


Coolant enters manifold and exits manifold. Raw enters spacer and exits in throat of exhaust hose.

With blocking on top coolant enters exhaust manifold and exits spacer. Raw enters riser and exits into exhaust
 

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