Gasket for exhaust elbow

[Rich Kuehne]

Have a question about the exhaust manifold assembly and a gasket. The manifold is attached to a riser or elbow. The riser goes up into an upside down U and then out the exhaust. Coolant travels through the manifold assembly and then back to the exchanger. The U requires a gasket at the top. The gasket has one opening at top dead center for the coolant to pass through as is keeps the entire manifold assembly at tempreture. The mainifold has around four openings for the coolant to flow through. However, this gasket blocks three of these. Would there be a reason for this.
They are Crusaders, 454, fresh water cooled.
Thank you
Rich

[MikeP]

Yes, this is by design. DO NOT open the other holes in the gaskets. THe point is to ensure that the water fills the elbow/riser and that there are no hot spots.

[yachtsmanbill]

Correct!! My gas boat had a block-off plate and 2 gaskets.( MERC 330s ) I milled out a new 1/2" thick plate and drilled and tapped for an EGT thermocouple. Longer studs were also necessary. Have yet to hook meter up. Check carefully for water and exhaust leaks when finished. Use lots of P-oil to prevent studs from breaking, and never- seize the new stuff !! ws

[Rich Kuehne]

Thank you for the information. No plans to modify the gasket, just did not know why the four water chambers were there and then have three blocked by a gasket. Makes sense that it will keep the unit at temp.

Well this is the weekend for the shake down run. Rebuilt 454s and trans. All sound great. All fluids are pumping and the temp is stable. One more check on the clamps and hozes. Install the gasket on stbd riser and we are off.

Thank you
Rich

[yachtsmanbill]

FYI -- mine were originally Raw water cooled and all 4 passages were for exhaust cooling-- the block offs keep the heat exchaner water in. The r/w style needs an additional cooling line off the thermostat by-pass to cool hoses and one to cool manifold -- hope this helps. The mercruiser manual show the systems in great detail. ws