Converting 5.0 mpi to closed cooling

[Searay205]

Hello,

I have a 2011 Mercruiser5.0 mpi Catalyst engine. Just dropped $1600 on manifolds and risers. Does anyone have any experience with converting a salt water engine to closed cooling? My new manifolds have zero scale, I am wondering if my engine block has enough rust scale that it will cause plugging issues in the exchanger.

On a side note the manifolds are extremely heavy and awkward. 70Lbs for manifold and 20 lbs on riser. My current ones are 10 years old and I decide to replace at 260 hrs 100% saltwater use. I can handle the manifold now but in 10 years I wont be able to LOL. How the head bolts dont shear off due to weight is a mystery. Thanks in advance!!!

 

[Bt Doctur]

get a lete model 5.7 standard carb,efi,or mpi package and drop the cats

 

[Scott Danforth]

Hello,

I have a 2011 Mercruiser5.0 mpi Catalyst engine. Just dropped $1600 on manifolds and risers. Does anyone have any experience with converting a salt water engine to closed cooling? My new manifolds have zero scale, I am wondering if my engine block has enough rust scale that it will cause plugging issues in the exchanger.

On a side note the manifolds are extremely heavy and awkward. 70Lbs for manifold and 20 lbs on riser. My current ones are 10 years old and I decide to replace at 260 hrs 100% saltwater use. I can handle the manifold now but in 10 years I wont be able to LOL. How the head bolts dont shear off due to weight is a mystery. Thanks in advance!!!

Dont worry about the motor. In 10 years the block will be rusted thru

Yes, you already have too much salt buildup and rust to put an HX on

To put a HX on your boat, you will need a new block and heads and intake.

Run the boat as is, enjoy it as is, then sell it and buy a boat with an HX

 

[Searay205]

Good point who know where the boat will be in10 years. Makes sense!

 

[alldodge]

2011 and CATs, have always heard CATs came in during 2014

 

[Searay205]

Cats started CA in 2008. Mine is a 2011 and it has them and boat was purchased in FLA. Funny thing is the 2011 V6 and carb V8 doesn't have them. In 2012 I believe they dropped the carb option and they all have Cats. My doesn't have cats as I have eliminated them. Cats aren't the problem its the increased complexity of the PCM. I would be shocked if outboard dont have cats by 2024.

I debated retrofitting to the old manifold style but between finding new old stock, guy that bought risers and didn't need I got my total price down to what it would cost to convert to old style manifolds using Mercruiser parts. Sticking with "cat manifolds" is plug and play and avoids any questions when sold. I can easily reinstall cats if i wanted to but who would....

 

[QBhoy]

Your manifolds will last longer if you flush them out and fill with AF each winter. Strongly believe the damage is done to manifolds on salt boats...mostly when they are in storage and lying damp and empty. Your block will last longer than you will..if you leave it full of AF during storage

 

[Searay205]

I agree oxygen content is much lower in water than air lol. I keep my engine full of water, except a month ago when Houston hit 19F. I agree with engine lasting 4ever. Had a 3.0 liter that was 35 years old when sold, flushed after each use and kept full of water. manifold if flushed only fail at back side of exhaust passages where hot exhaust gases boil the water resulting in erosion/corrosion.

 

[Lou C]

At least here in Long Island (definitely salt water maybe not as salty as Fla) your block and heads will not rust through in only 10 years, when I had my engine apart in 2017 it had been used in salt more than 15 years (15 just by me, not sure about previous owners but I bought it here so it could be as long as 20 years then). When I had the heads off due to blown head gaskets the cooling passages in the block had a lot of scaled up corrosion but not rusted through anywhere. The heads, what happens is that the cooling passages start to erode and might not seal against new head gaskets. The machine shop I went to recommended replacement so that's what I did. I had been filling it with AF every winter. I've always heard both sides of this debate (it helps so do it & there isn't enough O2 inside the engine (assuming you replace the drain plugs etc) to cause corrosion in storage. Who knows for sure?!
To me it's the same as spraying engine oil pans with Corrosion X or trailer leaf springs, you do that and they last 2x as long if not longer. My 1988 has the original oil pan, its been moored in salt water nearly 20 seasons. You isolate the metal from oxygen.
But to answer the OPs question no I would not try to convert a run in salt cast iron engine to closed cooling. You will never get all the rust out of it and it will last as long as it lasts.
I think here you can figure on getting 15-20 years before you run into problems due to salt water corrosion AS LONG AS the exhaust system is properly maintained. I have heard of heads rusting through behind the valves or intakes rusting through, but never heard of blocks rusting through.
So if you're trying to make yours last as long as possible one thing you could do is replace the cyl heads at about 15 years of raw water cooling, this is fairly easy job to do with the engine in the boat as long as you have good access.
To those with CAT engines, if there is no inspection for boats where you live, what are the legal repercussions of removing the cat exhaust? I can't imagine these abominations on an outboard.

 

[QBhoy]

At least here in Long Island (definitely salt water maybe not as salty as Fla) your block and heads will not rust through in only 10 years, when I had my engine apart in 2017 it had been used in salt more than 15 years (15 just by me, not sure about previous owners but I bought it here so it could be as long as 20 years then). When I had the heads off due to blown head gaskets the cooling passages in the block had a lot of scaled up corrosion but not rusted through anywhere. The heads, what happens is that the cooling passages start to erode and might not seal against new head gaskets. The machine shop I went to recommended replacement so that's what I did. I had been filling it with AF every winter. I've always heard both sides of this debate (it helps so do it & there isn't enough O2 inside the engine (assuming you replace the drain plugs etc) to cause corrosion in storage. Who knows for sure?!
To me it's the same as spraying engine oil pans with Corrosion X or trailer leaf springs, you do that and they last 2x as long if not longer. My 1988 has the original oil pan, its been moored in salt water nearly 20 seasons. You isolate the metal from oxygen.
But to answer the OPs question no I would not try to convert a run in salt cast iron engine to closed cooling. You will never get all the rust out of it and it will last as long as it lasts.
I think here you can figure on getting 15-20 years before you run into problems due to salt water corrosion AS LONG AS the exhaust system is properly maintained. I have heard of heads rusting through behind the valves or intakes rusting through, but never heard of blocks rusting through.
So if you're trying to make yours last as long as possible one thing you could do is replace the cyl heads at about 15 years of raw water cooling, this is fairly easy job to do with the engine in the boat as long as you have good access.
To those with CAT engines, if there is no inspection for boats where you live, what are the legal repercussions of removing the cat exhaust? I can't imagine these abominations on an outboard.

Hi Lou. There would be literally all the O2 in the world available to the engine...even with the drain plugs back in. Of course. It’s wide open to the atmosphere when the boat is out the water in storage and left not filled with AF. No doubt about it.

 

[Searay205]

easily remove cats with zero issues except alarm but there is a device that sends a signal to PCM. Post cat O2 sensors only purpose is to tell the PCM the cats are working. PRecat o2 very important determine air fuel mixture. the problem with cats engines vs non cat engines it the multitude of additional alarms the cat engine have.

No worries CA is requiring cats in all outboard motors and PWC by 2028.

Another disadvantage of cats is the manifolds weigh 75lb vs 40lbs and the cost is high, again replacing every 10 years digestible every 3-4 ridiculous. Funny cat engines are still cheaper than new outboards per hp. For example a new 350 mag mpi with cats is $13k. A 300hp outboard is $20K without cats....

 

[Lou C]

Its things like this that make me keep the old one!
Set of points & condenser and a Quadrajet rebuild kit (less than $100 parts) and there you go. The "benefits" of technology are greatly over-rated.