Dry-Joint Exhaust ??

Something to note on the 8.1S exhaust system than generally doesn' get mentioned. The bottom of the manifold has a drain. This allows the entire system including the heat excangers (water, oil and trany) to drain dry. Hence, why there is no zincs on the 8.1s. Which also helps with extended life. Ever look at the side exhaust on first start and it takes several seconds for water to spit out. Well that's why.... the system is refilling.
 
Something to note on the 8.1S exhaust system than generally doesn' get mentioned. The bottom of the manifold has a drain. This allows the entire system including the heat excangers (water, oil and trany) to drain dry. Hence, why there is no zincs on the 8.1s. Which also helps with extended life. Ever look at the side exhaust on first start and it takes several seconds for water to spit out. Well that's why.... the system is refilling.[/

That’s handy. Does it just drain into the bilge?
 
That’s handy. Does it just drain into the bilge?
No, out the drive or out the shaft seal depending on your set up. Lowest point out to sea level.
 
No, out the drive or out the shaft seal depending on your set up. Lowest point out to sea level.

Ah, ok. I always wondered about why it took a few seconds before it started ‘spitting’. I also was hoping the draining was going to be a simple explanation for the water that’s always in my bilge (even a day after sucking it all out) but that’s a different thread. :)

Thanks! I’m going to sleep better tonight. :)
 
There have been issues with 8.1's of engine damage from leaking manifolds, so they should still be checked periodically. The main problem was with the all aluminum manifolds that were being used all the boats - either fresh water or salt water. The salt water boats had issues due to the salt water corroding the manifolds from the inside out (rather quickly). Some got lucky and the corrosion hole would show on the outside of the manifold which could be spotted by a watchful eye in the engine room. Others weren't so lucky and the corrosion hole was thru to the exhaust gas side of the manifold causing water to drain back into the exhaust valve areas upon shut down. This caused exhaust valves to rust and could also be enough water to hydrolock a cylinder if the exhaust valve was left open upon shut down. Once the engine was restarted with a cylinder full of water - BANG! Engine ruined.

Now, with cast iron manifolds the time it would take to have the same corrosion problems is longer vs aluminum, but not eliminated. In time, the cast iron ones could still leak internally due to corrosion and cause the same issue. Don't be thinking that a "dry joint" exhaust will never have internal water leakage problems - they just won't leak from the joint - instead it could be a pinhole through the casting caused by corrosion.

I operate in fresh water and have the aluminum manifolds and am confident that they will last 20+yrs. You may want to get other's opinions as to the expected longevity of cast iron manifolds in salt. From what I've seen in other posts, it is difficult to inspect these manifolds for future corrosion issues within the chambers. Once they leak, the damage is soon to follow!
 
Interesting how aluminum exhaust manifolds corrode quickly in salt, but the aluminum Y pipes don't ?
 
Interesting how aluminum exhaust manifolds corrode quickly in salt, but the aluminum Y pipes don't ?
Big part of the problem was the drain on the aluminum water rail below the aluminum manifold had a stainless fastner. Now mix aluminium, stainless and salt and you have a very basic battery. The result is a plugged drain due to heavy corrosion and then the saltwater could not exit the rail or manifold exasperating the battery effect.. I went thru this when I got my 410. From fresh to salt and in 6 months water rails were shot and major pitting in side the manifold. Changed all to cast and all good. I plan every 6 years to change the manifolds due to saltwater. Just the price of saltwater cruising.
 
There have been issues with 8.1's of engine damage from leaking manifolds, so they should still be checked periodically. The main problem was with the all aluminum manifolds that were being used all the boats - either fresh water or salt water. The salt water boats had issues due to the salt water corroding the manifolds from the inside out (rather quickly). Some got lucky and the corrosion hole would show on the outside of the manifold which could be spotted by a watchful eye in the engine room. Others weren't so lucky and the corrosion hole was thru to the exhaust gas side of the manifold causing water to drain back into the exhaust valve areas upon shut down. This caused exhaust valves to rust and could also be enough water to hydrolock a cylinder if the exhaust valve was left open upon shut down. Once the engine was restarted with a cylinder full of water - BANG! Engine ruined.

Now, with cast iron manifolds the time it would take to have the same corrosion problems is longer vs aluminum, but not eliminated. In time, the cast iron ones could still leak internally due to corrosion and cause the same issue. Don't be thinking that a "dry joint" exhaust will never have internal water leakage problems - they just won't leak from the joint - instead it could be a pinhole through the casting caused by corrosion.

I operate in fresh water and have the aluminum manifolds and am confident that they will last 20+yrs. You may want to get other's opinions as to the expected longevity of cast iron manifolds in salt. From what I've seen in other posts, it is difficult to inspect these manifolds for future corrosion issues within the chambers. Once they leak, the damage is soon to follow!

Thanks ...this is exactly why I am concerned. Not because I have aluminum, but I am pushing sea water through a cast iron manifold so corrosion is bound to happen eventually. That and I have no idea how old the iron manifolds are. I will talk to my mechanic this spring and go with his recommendations.
 
Thanks ...this is exactly why I am concerned. Not because I have aluminum, but I am pushing sea water through a cast iron manifold so corrosion is bound to happen eventually. That and I have no idea how old the iron manifolds are. I will talk to my mechanic this spring and go with his recommendations.


If cold saltwater then 5-8 years. Warm saltwater slightly less.
If freshwater up to 20 years.
 
Dry joint vs. Wet joint are completely different in design. The water passage for wet joint exhaust is right at the connection between the riser and manifold. The water passage for a dry joint setup comes from an offset connection several inches back from the joint itself. The wet setups fail when the small sealing area corrodes and then water drains back down to the cylinders. You just don't have those issues with a dry joint setup.

The only thing I may consider with a dry joint setup is to install a flush system for salt water applications. Otherwise, run it and enjoy.

Take a look here. It should be much more apparent - http://www.mooreperformance.info/Mercruiser-V6-manifold-kit-2002-2003-2004.html

Doug

Just bought a 1999 Sundancer 310 Inboard, 5.7 Blue water MPI small block, raw water cooled, 400 hours on engines. Engine was in Lake water for 20 years. Pristine. Compression 180+ in all cyls... First time in Salt water is with me :)

I asked the local merc rep if they would do a conversion to fresh water cooling - which I knew would be roughly $3.5K per engine - and he said that in his opinion it wasn't worth it. He said the engine would have other issues before I could leverage the investment. The guy sounded honest enough to recommend I just install a good flushing system and flush it systematically. I did install Perko flushing strainers and the west marine salt off applicator.

Then I read about the wet/dry joint exhaust and asked him and he said he didn't know about it but probably would not work on my model. If i look at the parts, they all look like they could fit since the manifold for small block was the same for a while...

Any thoughts?

One of my engine serial numbers is L302260

Is there any specific version of the small blocks from 1999 that may or may not work with dry joint exhaust?

Fer
 
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mercruiserparts.com Find a closed cooled sbc and all the hoses will have part numbers. Mercs heat exchangers are pricey so you can do better with aftermarket like Seacamp, Mr. Cool, etc. Merc hoses will work with their coolers

Look at engines with a 0W prefix.they will have dry-joint. Try this number 0W345831
 
So manifold & riser dry joint is a good idea but closed cooling is also a good idea. You'd have to go aftermarket because Merc is really expensive. I bought a lake boat in August 2020 and last winter had it converted from raw water cooled to closed cooling and no regrets. So the expense of dry joint manifolds for your application if you also do closed cooling is better because the manifolds are part of the closed cooling loop and will last much longer. Raw water cooling means manifolds & risers every five years.
 

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