Mercruiser Catalyst Manifolds are Lifetime / No replacement necessary

[Searay205]

Wanted to followup on Mercrusier Catalyst manifolds. 2010 Mercruiser 5.0 MPI used in saltwater for 300 hours. Flushed 90% of time. No other treatment but flush. Run hard. I ordered and replaced my Mercruiser catalyst manifolds $2000. It was a waste. Original manifolds looked fantastic. I removed freeze plugs scraped away some black crap/marine garbage and like new black coating underneath. Manifolds would have lasted life of engine. PERIOD, do not replace manifolds. On to risers. Discharge of riser that goes into rubber connector completely corroded, I had to bust it out of boot. On bottom of riser on discharge side there is tube that discharges water which is in addition to the the casting passages, it was the only way water was exiting the riser/engine. Surprised it wasn't overheating but it wasn't (verified with Rinda scan tool). So Riser needed replaced due to end condition BUT actual riser where there are water passengers wasn't thinned or corroded to any extent. I took a drill and drilled numerous holes and found full thickness. I checked right were superheated exhaust hits after exhaust passes through catalyst so its the worst environment. Bottom line if engine not overheating run the manifolds and risers indefinelty, if overheats and can find reason check risers. I found large chunks of rust in my outdrive when doing water pump for years, guess I know where it was coming from, the riser where the water and air mix. Doestn hurt anything as long as you still getting enough water to pass through. Nobody makes aftermarket cat manifolds so if you have cat manifolds you have lifetime manifolds no replacement necessary!!!!!

Mercruiser in early 2000 started use a EDP coating on the cooling passages on engines, heads and a little after that manifolds. Its works. I changed many manifolds, Found many corroded and thinned. I found Zero with the Mercruiser catalyst manifolds. I found this out from a guy that worked for Mercruiser in the 80-90's. Sounded like he knew what he was talking about, he was selling coating for pump volutes etc( I work in petrochemical industry). I could even see the casting ridges and seams, Unreal. Well I hope I save someone some $$$$$. Great job Mercruiser! My boat is seawater cooled, no closed system. I have a lot more details on the coating applied on the Searay forum I posted back in 2018.

 

[achris]

My 2006 4.3MPI is still on original manifolds. They are also EDP coated.

 

[Searay205]

Mercruiser product manual says for corrosion protection EDP coated manifolds and dry-joint risers. Soooooo does that mean the risers are EDP coated and are dry joint or just dry joint. My guess is just dry joint as my risers has extensive corrosion at the discharge which is irrelevant. If your 2006 has them which is the old style manifolds I would only go back with mercruiser if one did need replace (freezing?) as I seriously doubt the aftermarket manifold makers utilize EDP coating. I like to crap when I scraped the crud off and there is a shiny coating. Oh well life goes on....

 

[tpenfield]

I have twin 2016 Mercruiser 6.2L engines (with CAT's) on my new-to-me boat. The engine block and exhaust manifolds are closed cooled (coolant). So it is just the risers that I need to be concerned with.

Perhaps I will check them in a year or 2 to see how they are holding up in the salt water. The boat has been in salt water seasonally since 2016.

It would be great if the risers held their own and did not need frequent replacement.

 

[achris]

Mercruiser product manual says for corrosion protection EDP coated manifolds and dry-joint risers. Soooooo does that mean the risers are EDP coated and are dry joint or just dry joint. My guess is just dry joint as my risers has extensive corrosion at the discharge which is irrelevant. If your 2006 has them which is the old style manifolds I would only go back with mercruiser if one did need replace (freezing?) as I seriously doubt the aftermarket manifold makers utilize EDP coating. I like to crap when I scraped the crud off and there is a shiny coating. Oh well life goes on....

Not sure what you're asking here. (I've read it three times and I'm still confused).

All Merc manifolds, risers and elbows after 2002 will be dry-joint from factory.

I have dry-joint (being 2006) manifolds and elbows (no risers), and I replaced the elbows about 7 years ago. The old ones were pretty crusty at the outlet end. From what I remember reading when I was looking at buying this engine, the manifolds and elbows are ceramic coated before being EDP coated, and I suspect it's the ceramic coating that gives the protection, not the EDP (Electro-Deposition Paint), it's just paint after all.

Chris..........

It also appears you are referring to 'risers' when you mean 'elbows'. As risers are also a part of some exhaust system setups, that becomes confusing. Here's a diagram from Merc's own manual on the terminology...

 

[Searay205]

Thanks!!! I never knew risers and elbows were different, thought same part. On the catalyst engines there are no risers. Elbows come in different "lengths/heights".

I busted my elbow apart with sledge hammer to inspect the water jacket thickness. Tons of inner wall left, some plugging. I wouldn't touch manifolds or elbows unless you are getting engine temp issues.

tpfield,
I would guess your elbows will be "frozen" in your rubber connector from the swollen rust. The ends do get corroded (no harm) its where the exhaust and water meet. At the same time you will be messing around with your very delicate catalyst$$$$$$$. I would not touch!!! Let them live there life for decades. With the closed cooling you are golden.

I removed my catalyst 3 years ago (in my attic in a box). I Got tired of replacing my rear oxygen sensors every 18 months at $100 each (rear only). Used the Max Volt simulator $420 which was plug and play. I see another company makes a simulator for $89 but you need two so $190. The Max Volt Works flawlessly!!! Oh exhaust smells like exhaust now instead of skunk and no more predentination when running 87 octane when wide open (most of the time lol).

 

[QBhoy]

Hi..I am also a little confused about what is being asked...But got me thinking about a cat exhaust fitted on an engine identical to mine and only 7 years younger...where is the cat actually located in the exhaust and does it reduce her power at all ?
Also thought it a good excuse to show off my lovely, immaculate, near 20 year old mpi and her full Corsa Marine system...

 

[QBhoy]

here she is...one of her big side exits on show

 

[tpenfield]

My new-2-me boat has CATS (sometimes it will have dogs too ). I should take a picture of the exhaust today. Nothing posted so far looks like them. Model year 2016.

 

[tpenfield]

Here are some pictures of the CAT Exhaust of my Merc's . . .

They are Seacore 6.2/350 HP 2016 vintage. (S/N's in signature)
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The manifold/CAT portion is part of the closed cooling system. The elbow/riser at the end of it is the portion that is (and has been) exposed to sea water.
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I am just wondering if the elbow/riser is going to need the typical periodic replacement ???

My previous boat had the old school 7.4L with full closed cooling and stainless steel elbows. It was about as maintenance free as you could get in salt water.

 

[Searay205]

Sorry for the late response. I wouldn't replace the elbows until they restrict water flow leading to high engine temps which could be decades. You have no risk as far as corroding through to combustion side. I busted mine apart and even thought the bottom 1/3 was rotted off in the aluminum pipe going to transom the wall thickness of the elbow that could leak water into the exhaust side was 1/4" thick. My manifolds were in exceptional condition. Remember the discharge of the elbows is where exhaust gas and water meet, very corrosive environment but who cares, going out back of boat anyway.