small corrosion from bad manifold

[_vn_]

hi, just took off risers and manifolds from mercruiser 6.2 mpi 2002 built
both manifolds seems to be in good condition, no corrosion inside, risers also seem to be OK
when looked into engine ports on port side i noticed some corrosion spots.
i will be replacing both sides manifolds/risers, however - what do i need to do about those corrosion spots? do i clean them or let them burn trough ?
thanks !

 

[Grub54891]

We like pictures!

 

[Scott Danforth]

Need pics

Just helped a friend with a 2004 6.2 that was taken out by his manifolds

Failure mode appears to be rust thru on the manifold

If you have the single point drain, you may want to check the lower block hoses and the manifold drains

 

[_vn_]

here are some pics, i tried to find some with inside manifolds - but i didn't see any,

 

[Ncherry84]

Myself personally....I wouldn't worry about cleaning up that little bit. I'd just run it. A properly tuned motor would just burn that out and carbon over it. May have inadvertently got some moisture in there somehow....but for that little bit and so much material there it would be decades if ever before it became an issue.

 

[Grub54891]

Looks like just condensation surface rust. Not an issue. Bolt her together and run it.

 

[_vn_]

Looks like just condensation surface rust. Not an issue. Bolt her together and run it.

hi, are you saying i can still run those manifolds and risers? i had this boat for 5 years, at least third owner.
kept it in the lake, fresh water, always trailered. just brought to Long Island this season, however also trailered and always flushed out with fresh water. i have no idea if those manifolds and risers were ever switched, however they look like they only have carbon inside, even layer, no funky stuff. when opened risers no rust clusters leaked out, just some brown water. i'm in front of a dilemma, should i spend 750 now or let it run?
the reason i opened them is i was in the ocean couple weeks ago and engine was cutting out on low rpms but going back on on its own, eventually it stalled out. when restarted it ran really rough and metal clunking was heard. i noticed that oil was low and after adding some oil - it ran good all the way back to inside the bay, however when parking it at the beach it would cut out on low rpms. i was running mercury vessel view mobile and it threw overspeed code, since this vesselview can only give you current codes i'm not sure what was it a result of, but mercury support tech suggested i get it further diagnosed. i already have rinda coming on wednesday but had this itch to open manifolds since every person i spoke with points to them. also boat had been starting hard lately, increasingly hard, i had to press button to open choke up when cold started for last 4-5 times. to spend or not to spend - that is the question

 

[jakwi]

That is the $1000 question that no one will really want to answer.

Here is what you know for sure, you have water in your exhaust ports.

This indicates a leak, either from a failing gasket between the risers and manifolds or from corrosion in the manifolds themselves.

Generally, from what I've been told manifolds and risers hold up much better in fresh water, so it may be that you are fine, but the risk is yours, as a mistake can very well cost you your motor.

If you think the risers look like they only have surface rust inside then you could have the mating surfaces decked, and then put a fresh set of gaskets on them, and complete a pressure test, but remember that a passing pressure test today is no guarantee that it will pass tomorrow.

Surfacing the mating surfaces in my area is about $20 per surface, with a 3 inch spacer in my case that was $80 per side, so $160 plus another $20 to $30 in gaskets for a maybe. In my case I am running in salt water and it had been 7 years with questionable care from the PO. So I bit the bullet and replaced them. By pure visible inspection I was tempted to give it a shot, but in the end it's a lot of money to lay out for a maybe.

Only you can decide what is right for you. If you have a friend with a machine shop, and the resurfacing doesn't cost you anything, then Hey give it a shot.

For me the peace of mind, just knowing that they are in good shape was worth the money.

oh, and one of the symptoms I had before I replaced mine is that it would start hard if I left it to sit for more than a few days. and it would take a really long time to warm up and settle into a smooth idle. 20 minutes or so after reaching temp. I think, but don't know for sure, that it was taking that long to burn off the water that was sitting in the bottom of the manifold.

Good Luck

 

[Scott Danforth]

the pictures show condensation from not being run. this is common in a marine engine when you have condensation as well as water in the water jacket and high humidity in the exhaust pipe

clean the gasket surfaces, acetone check and pressure check the manifolds, replace them if you want/need. bolt them up and go boating.

fresh water manifolds usually last decades. salt water manifolds die between 5 and 10 years

however that little bit of rust in the exhaust is nothing. the exhaust ports on my motor sitting on a pallet in my garage rusted more than that.

below is what happens when the dry-joint manifolds fail..... after 7 years of salt water with a rack stored boat that is flushed after every use. the manifolds fail, leak water into the ports and the motor hydro-locks. then when the marina mechanic doesnt look at the boat for 6 weeks..... results in a new engine.

 

[_vn_]

the pictures show condensation from not being run. this is common in a marine engine when you have condensation as well as water in the water jacket and high humidity in the exhaust pipe

clean the gasket surfaces, acetone check and pressure check the manifolds, replace them if you want/need. bolt them up and go boating.

fresh water manifolds usually last decades. salt water manifolds die between 5 and 10 years

however that little bit of rust in the exhaust is nothing. the exhaust ports on my motor sitting on a pallet in my garage rusted more than that.

below is what happens when the dry-joint manifolds fail..... after 7 years of salt water with a rack stored boat that is flushed after every use. the manifolds fail, leak water into the ports and the motor hydro-locks. then when the marina mechanic doesnt look at the boat for 6 weeks..... results in a new engine.

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this looks very different from what i have did you flush it out with just water or used some kind of saltoff or similar?

another thing i remembered is that starboard side riser ran noticeably hotter (could not keep hand on it for longer than 3-5 saeconds), i think in range of 30-50F hotter than port
when i pulled water hose from starboard manifold a lot more water came out of it than port side also.

 

[Scott Danforth]

this looks very different from what i have did you flush it out with just water or used some kind of saltoff or similar?

another thing i remembered is that starboard side riser ran noticeably hotter (could not keep hand on it for longer than 3-5 saeconds), i think in range of 30-50F hotter than port
when i pulled water hose from starboard manifold a lot more water came out of it than port side also.

the motor is toast. it was replaced with a new reman from Mercruisers

its on a pallet and will be parted out.

regarding your water flow. pull the whole hose assembly and clean out the hoses. there may be a blockage somewhere if you have a significant water flow difference.

 

[Grub54891]

Lets see: I have three rigs, two from 1984, one from 1985. All fresh water, manifolds still fine.

 

[_vn_]

so i ordered the new setup for 750, might save 400 or so but i'd rather have piece of mind that manifolds are fine for next 3-5 salt water years of boating
i can probably mate, clean and test them for free but it will take me some time and i'd rather have another few boat outings this year
thank you all for provided input !

 

[Lou C]

I replaced mine every 5/6 seasons here in Long Island Sound region and never had water in the engine from the exhaust. Accept it is part of salt water boating and move on....

 

[jakwi]

From what I've read, and experienced, a temp difference between the port and starboard side is fairly normal due to the flow through the thermostat housing. How much that difference is, and what is normal is the real question. I think, and bear in mind I've only had one of these boats, that so long as the rubber hose that connects the riser/elbow to the Y-pipe isn't smoking and melting then probably you're ok. The real issue, as far as I can tell is that you don't want to melt the flapper valve, which is rubber and directly in the flow of the exhaust. (you should probably replace the flapper valves while doing the other work) After the flapper valve you could probably consider exhaust gas flow dynamics when cooled versus not cooled on both sides of the engine, but in my mind the difference will be so negligible as to not matter at all, unless you are running a really high performance engine at high rpms

As Scott said a blockage on one side could cause a temperature difference, so no disrespect is meant, and I have to say I noticed a difference in temp just like you. Someone on this forum, probably Scott, mentioned a possible blockage. When I replaced my manifolds I pulled all of the lines, and replaced the thermostat. I inspected everything as much as I could, and it was all wide open. Even the manifolds didn't look that bad. In the end, with brand new manifolds, risers and elbows, the temperature difference was basically the same. I didn't measure it with anything but my hand so I can't say for certain that it didn't change at all. I think it is just the way it is.

One FYI though several weeks after I changed everything out I had a hose clamp break right in the middle of the band. Salt water is amazing. It could have sunk the boat, so my advise is to buy good quality new clamps and replace them all when you do your manifolds.

 

[jakwi]

below is what happens when the dry-joint manifolds fail..... after 7 years of salt water with a rack stored boat that is flushed after every use. the manifolds fail, leak water into the ports and the motor hydro-locks. then when the marina mechanic doesnt look at the boat for 6 weeks..... results in a new engine.

Good lord this is my worst nightmare. It makes me want to drain the manifolds every time, but I know that makes them rust worse. It seems like they would have come up with a downward flowing manifold so this couldn't happen.

 

[Lou C]

The only cure for this is prompt replacement. It may be that having the dry joint system lulls people into a false sense of security. While the joint between the manifold and elbow won't deteriorate as fast as the old style wet exhaust joint, the elbows or manifold still can and will rust through! If in a high corrosion area (and Fla salt water certainly is) 3-5 years is what you may have to do. Here our season is shorter, water is less salty so 5-7 works without exposing you to excessive risk. I am now on exhaust system #4 on my engine. 3 sets of the original OMC one piece units (never had leaks from these) and the latest the 2 piece Volvo style conversion as the one piece batwings have been NLA for many years.
You can also test them by removing off the boat and prop them up level and fill with acetone (careful flammable) to see if it leaks in any of the exhaust ports, acetone has less surface tension than water...