Exhaust riser gaskets

[SCORPIO]

I'm going to pull my elbows to inspect them and the manifolds for corrosion/wear. What style gasket should be used on an engine with a half fresh water cooled system? (Manifolds and risers have salt water running thru them). I see the restrictor style with two oval slots and two small holes and I also see what are listed as 'full flow' gaskets. I've always had raw water engines up until now and they used the restrictor style. I would imagine the FWC engines need more flow to dissipate the heat from the exchanger. Does anybody know for sure? I want to have the gaskets in hand when I start the job so it doesn't drag out into several days waiting for parts to show up. Thanks!

 

[Espos4]

Do you have spacer blocks?
If so, there are 2 gaskets per side.
I have spacer blocks and 1 restricted flow and 1 full flow gasket on each side.

They are a bit pricey, about $35-$40 each.

 

[SCORPIO]

No spacer blocks, just the manifold and elbow.
I read a Merc service bulletin #99-10 dated Jan 2001 and it states that, 'CLOSED COOLED ENGINES WITH RAW WATER FROM THE HEAT EXCHANGER GOING TO THE 90-DEGREE FITTING ON THE BOTTOM OF THE EXHAUST MANIFOLD: USE P/N 27-863726 GASKET- 4 SLOT BETWEEN THE EXHAUST MANIFOLD AND THE EXHAUST ELBOW.' This is how my system is set up, so I'm thinking I should be using the four slot 'full flow' gaskets. I have also read posts on various forums stating that you need the restrictor gasket to keep the manifold full of water. I don't know how the manifold could run low on water since it is being fed from the bottom by the outdrive water pump and water can only exit as it is pushed out by new water coming in from the drive. Am I over thinking this or is there some suction effect caused by the exhaust gas leaving the elbow that could pull water out of the manifold faster than the pumps ability to replace it?
Just don't want to make a mistake here with brand new ( in the last three years) engines.

 

[Espos4]

To clarify, I have dry joint manifolds.

I see you have a 1999 which I presume are non-dry joint.

Different gaskets. My only recommendation is to use the same style that you already have in there. I know this doesn’t help your quest to pre-purchase the correct gasket. Sorry.

 

[Strecker25]

The key that I’ve read is how they’re fed from the t stat. You mention the 90* elbow at the manifold, is that the only water feed to the exhaust? If so, I believe full flow. If you have hoses also going to the elbows, restrictor.

Edit, not tstat in your case but same idea jus coming from HE

 

[SCORPIO]

These are NOT dry joint. They are the older center riser style manifolds. They are fed by only one hose on the bottom of each manifold, nothing feeds into the risers. So only one hose each side.
The old engines had the four hose system but the new ones are single hose bottom feed.