Mercruiser exhaust riser plumbing

[SWBuechler]

I have replaced the engine in my 1979 Bellboy and, in the process converted from log style exhaust to center riser exhaust. I have searched the shop manual and can not figure out how to hook the various hoses up. The cooling system uses both coolant and raw water. Raw water comes in through the stern circulates through the heat exchanger and then, some how, expels through the exhaust. I can't figure out if the hoses go through the risers or just to the exhaust manifolds. Additionally, the gaskets between the exhaust manifolds and risers confuse me. It seems to me no coolant should enter the exhaust manifold OR risers but I can't see how to prevent that. I guess what I'm looking for is an understandable diagram showing the plumbing for a V8 5,7 L Chevy exhaust system with a pre alpha (R) mercruiser outdrive. Any help will be appreciated.

 

[Bt Doctur]

Does the heat exchanger have the capacity to cool the manifolds or just the engine? If your using A/F in the manifolds you need a block-off plate between the riser and manifold.and an additional hose fitting on the manifold. the water exiting the heat exchanger goes to a T fitting and then to each riser.
google Bluewater inboards 5.7 Wellcraft Coastal

 

[Bt Doctur]

 

[Bondo]

It seems to me no coolant should enter the exhaust manifold OR risers but I can't see how to prevent that.

Ayuh,...... Welcome Aboard,..... It could be plumbed either way,....

BD's diagram shows closed coolin' for Just the block,... probably how yer's should be,....

Other times, with a larger heat exchanger, the manifolds would be included, by usin' a block-off plate 'tween the manifolds, 'n risers,...
In that case, the raw water is expelled only through the risers, 'n coolant is in the manifolds, just as the block,.....

 

[SWBuechler]

That's VERY helpful. The heat exchanger does not have the capacity to cool the manifolds. I'm pretty certain that the manifolds are cooled with raw water. That brings the question of riser gaskets up. The gaskets that came with the risers look like the one pictured here. Do the slots go fore and aft or port and starboard? Also, whats up with the little holes on the opposing sides? It seems to me that if the intent is to block off two of the four sides then those little holes will defeat that purpose.

 

[Bt Doctur]

gasket only fits one way,their steam holes and are needed. the water exiting the heat exchanger goes to a "T" fitting and then to the bottom of the manifolds.