Need a little technical help please - effect of salt water on cast iron exhaust.

[TerryW]

Hi Folks,

My raw water (non-closed) exhaust system was overdue its 5 year strip down and inspection so I pulled it apart. I wonder if anyone can enlighten me on what is happening at the flange joints with respect to degradation please?

The photo shows an elbow that has been skimmed about 5 - 6 thou. It has had 6 years of use in salt water. If you concentrate on the flange between the water jacket and exhaust (near the bottom of the shot) you can see a dark area and some brown streaks. I watched the skimming process carefully. As the skimming proceeded, the dark areas changed shape but never got back a particularly consistent 3/16" of clean bright cast iron.

My question to the metallurgists out there is this: is the dark area where the porous structure of the cast iron has started to degrade?

If I get the piece milled will I actually find 3/16" of good flange?

Your help will be most gratefully accepted. Thanks in advance.

Terry

[Centerline2]

You are correct.... you can do nothing to stop it, which is the reason for the exhaust needing to be replaced periodically...
As the metal cools down after running, it has a tendency to absorb what it is in contact with.

dont bother with grinding more away, as what is seen is still strong even if stained... the elbows will need replacing to insure the SAME thing that is happening to the walls of the elbow doesnt cause an engine failure... long before the dark areas become a problem at the flange.

stainless exhaust components are less suseptible to this, but it is expensive and it does not last forever as some believe... but it does last much longer than the cast iron.

[Ruffryder]

This is why I always recommend EDP.

[builderdude]

Terry, it’s time to replace the exhaust components. I see rust scale on the interior of the exhaust chamber indicating either leakage at the gasket surfaces or worse, the parts are about to crumble apart.
Edit: this is the exhaust elbow, so leakage at the gasket surface wouldn't run uphill. IMO the elbow is starting to rust through.
Curios What the exhaust chamber in the manifold looks like

[boatworkfl]

When running salt water in a non heat exchanged engine you must flush with fresh water after docking.
Or buy stainless steel.

[RobMick]

Salt water is just brutal, the Volvo 5.0 in my Chaparral was replaced in 2015 by the previous owner....why they didn’t replace the exhaust elbows at that time is beyond me. Although this boat was stored “indoors” in SE Florida it’s entire life, I ended up replacing most of the wire connections throughout the boat, replacing exposed items like the horn and docking lights, shower heads...other nice “hidden gems” that were just eroded or I should say corroded away were the trim pump mount was shot and pump was laying on its side....it was never a factor really in deep water Florida, it I brought the boat up to Hell this past year to just what I am speaking about....to really tear into it and see what was what and address any issues. Looking at the boat overall, as you can see from the pics, for a 1999 she’s in pretty good shape...take away lesson I guess would be unless you really tear into the components under the deck, you will not know for sure how badly thensalt has taken its toll.

[RobMick]

Our 1987 Sea Ray 300, its whole life has been up north here in Lake Erie......she has none of the issue that my Chaparral does. Regular maintenance. Great, solid “tank” of a boat. Lesson....? Wait until you get up north and start your search for a fresh water boat...

[builderdude]

RobMick,
Although the sea water transfor port looks pretty rusted up on your Chaparrals exhaust elbow the exhaust chamber looks fantastic. No evidence of rust through compared to Terry’s elbow.

[wufibugs]

Hunter sailboats used Yanmar diesels in which the engine was a closed cooling ;system. The motor looked like it had been rebuilt fairly recently by the PO. The first time I took it out I got about 1000 yards before it overheated. Turns out the cast iron exhaust mixing elbow was completely obstructed with rock-hard carbon deposits. Although they do make a stainless replacement, it is prohibitively expensive. Access to sailboat motors is notoriously tight and removing and replacing the elbow was a job best left to a contortionist or someone with absolutely no other choice. Being the latter I did the job. From what I'm told this required maintenance every 8 years or so because there really is no easy way to flush the exhaust system of a boat that lives in the water. [One can allow the raw water pump to suck fresh water from a container that sits below the pump, but that's pretty difficult to accomplish on most sailboats where the pump is about 5" or less above the engine bilge. I've been told not to force or gravity feed water through the raw water pump as this risks damage to the impeller or getting water into the combustion chambers.]

[Pcpete]

Terry, don’t even mess with the old ones. Builder nailed it and those are engine killers. I’ve had good experiences with the aftermarket manifolds, even running partial closed cooling. Chief has some good advice about a fresh water rinse after being in the salt. I often use salt away as a wash down and would suggest using it in your rinse. When you are checking the manifolds in the future, give them a bath in muriatic acid overnight. It loosens the rust and you can get to good metal faster and cleaner.

[green650]

Not enough was machined off to clean off the mounting surface 100%. Removing only .005 is nothing. That’s not the problem though. It looks like your water passages are a little clogged by corrosion. I wouldn’t risk a motor and all the work replacing it by reusing those.
I think I paid around a thousand for new genuine Merc manifolds for a 454.

[Yendrabuilt]

Last year I blew out a elbow hose, so I pulled the manifolds/risers and they had a lot of rust flakes and muck in them. So I blasted them out with a pressure washer from every angle, probed with wire, blew them out with air, twisted three strands of fencing wire and ran them on a drill and got those flakes and the loose rust out. Having used products like Duro Extend and Rustoleum rust destroyer in the past, I thought what the hell why not dump some in and let it set in there and dump it out, and blow air for proper distribution and keep it from pooling. I don't know how it's working in there yet time will tell. I'll pull them again in the summer of 2020.

There is a cast iron kettle on my wood stove that I use to put humidity in the house during the winter. That kettle would have rusty muck in it every time I filled it, so I coated the bottom interior of it with Extend. Even after running out of water and getting the bottom hot multiple times, there is no more muck in the bottom. We will see it the stuff will work in an exhaust manifold.

Those little rust flakes that form in cast iron accumulate in the risers and it starts to block the out flow, there goes the hoses. 30 some years in an automotive machine shop I have machined a lot of cast iron, if you see thinning of iron in the gasket area you can count on the interior walls are thinning also.

[toy4two]

When running salt water in a non heat exchanged engine you must flush with fresh water after docking.

How is this done in a slip?

[boatworkfl]

For an out drive I believe you can buy muffs to do this, they are spring loaded.
You can take them to a radiator shop and have them cleaned if they are serviceable.

Google them.

[builderdude]

How is this done in a slip?

Perko flush pro is one option.
https://www.hodgesmarine.com/Perko-F...per0456dp7.htm
You could also plumb in a 3 way valve (bronze) to do the same.