I have a 1979 Uniflite with twin 270 crusaders. My engines have the half closed system, there is raw water in the exhaust manifolds. I saw a boat of the same vintage the other day and it looked like it had the same heat exchangers as mine yet it was a fully closed system. I am wondering if I could do the same. My heat exchangers do not have the extra pipes coming out of them. They are the 5" ones with the rubber caps held on with hose clamps. It would be nice to switch to the fully closed system without having to replace the heat exchangers. Anyone have this type of setup?
I do not have that exact setup, but I do have very similar units (twin SBC engines).
However, I have re-worked, repaired, replaced, altered and installed many Closed Cooling Systems over the years.
Usually when a Full System is required, the H/E (heat exchanger) is set up with the additional ports.
Maybe with the water temperatures in the Pacific Northwest the present heat exchangers could handle the increased load of keeping the manifolds cool as well...
While the seawater demand will typically undergo a very small change (going from a Half to Full Closed Cooling) if any, the size and heat exchanging ability of the shell-and-tube-bundle may change........ not to forget the additional ports within the E/G side (E/G = ethylene glycol) and a change to the T-stat housing.
In order to change this to a Full System, you will need to:
..... make sure that the H/E is capable of removing heat from not only the engine, but also from the exhaust manifolds.
..... see if the H/E can have the additional ports added to it.
..... make sure that your seawater pump is able to provide enough seawater.
..... block-off the seawater transfer ports between manifold and elbow.
..... you will need to change the T-stat housing as to accommodate coolant to/from the manifolds.
..... a means of splitting the "spent" seawater equally, and then directing it equally to the elbows. (elbows are always seawater cooled)
While I certainly like the idea of the Full System, I would ask myself if it's worth the effort and cost.