Exhaust Manifold water flow question

[nitedmn]

I have a boat with a '78 Mercruiser 898 (305) which I bought last summer. Shortly after buying it I had an overheating problem and I cracked both exhaust manifolds (the old "log" style mainfolds). I bought new Sierra manifolds and today I was working on putting the risers and end caps on them. After taking the riser off the old starbord manifold I discovered a metal plate between the manifold and the riser which appears to restrict the water flow to the riser. This plate only has ONE hole in it about the diamater of the tip of a pen. <br /><br />Should this plate be there? What would happen if I left it out?

 

[Don S]

Re: Exhaust Manifold water flow question

LEAVE THEM IN THERE. Did you honestly think they were installed just to make more parts for you to work with???????<br />That small hole is a vent to keep air pockets (and hot spots) from developing in the manifold. If you take it out, you will have water flowing too fast in the wrong areas and no flow where you should have and of course overheat problems.

 

[nitedmn]

Re: Exhaust Manifold water flow question

Thanks. That kind of what I thought but wanted to make sure.<br /><br />I guess I need to buy another gasket since the manifold I bought only came with one and I'll need a gasget for each side of that plate.

 

[Don S]

Re: Exhaust Manifold water flow question

You might also want to buy a Mercruiser OEM manual also. It might save you from makeing mistakes that you don't ask about.<br />You need book #3 for your engine.

 

[nitedmn]

Re: Exhaust Manifold water flow question

Thanks. That was on my list of things to buy but wasn't sure which one I needed. Now i know