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exhaust manifold corrosion

Gern BlanstonGern Blanston Posts: 138
edited August 2011 in Other Stuff
I have an Indmar MCX in my boat. I noted the other day that my exhaust manifold has some corrosion on it.  It is occurring in these small little "caps" that have been welded into it.  I think they are referred to as a sacrificial anode, but am unsure.  In talking to Indmar, I'm told that this occurs because of electrolysis - the water interacting with the aluminum.  He more or less implied that i should be draining the block after every time I ski.  No one I know does this except at the end of the year to winterize their boat so the comment struck me as....odd.  One of the caps corroded through the other day.  I temporarily repaired it by slopping some JB Weld onto it. 

The guy from Indmar further states that I should remove the manifolds, have them drilled out, and then have new caps welded in.  Or, I can spend approximately $1,100 and get a new cast iron exhaust manifold set.  I have no idea what kind of costs I'm going to run into having the manifolds, drilled, welded, and repainted only to have this happen again in approximately 6 or 7 years (my boat is an 05).  Has anyone else experienced this?  What did you do to correct the problem?  With all the aluminum blocks out there now, will this be an issue for them as well?

Additionally, I'm concerned that because Indmar changed the exhaust in 06, that I'm going to have ECM issues with the cast iron exhaust (should I go that route).  Is this concern unfounded?

thanks in advance for any insight or direction you can provide!


  • MCskiFreakMCskiFreak Posts: 323 Baller

    There are others that have experienced it too, going the route of having them drilled and patched is the easiest and cheapest option. There were a couple of guys over on TT that used JB weld, but I wouldnt recomend doing that. IIRC there was also a guy selling a set of cast iron manifolds on there.

    Matt Welton - Resident boat nerd
  • DWDW Posts: 1,825 Crazy Baller

    You can drill and tap the hole then install an anode that is threaded as opposed to welding one back in.  Easy to replace once used up.  They are available from Stainless Marine in Florida.  You want the anode as it is the sacrificial element in the system, and hopefully not the manifold itself.

  • eleeskieleeski Posts: 3,515 MM Trick Skier / Eccentric Person
    The cast iron manifolds on my 04 MC (replacements of the stock ones) corroded through. Being lazy, I JB welded up the hole (using JB Stick) It worked quite well. After a while the repair burned through. More epoxy putty. It's been several years now, the other manifold corroded through also. I found some high temp epoxy putty which lasts a bit better. But there is always a stick of putty in the boat for a needed quick repair.

    My old Nautique had a similar failure. I drilled out the hole and tapped in threads and screwed a bolt in with some silicone seal. This lasted quite well also.

    I had to buy new manifolds for the American skier. That wasn't too hard either as I had used anti sieze on the manifold bolts during an earlier replacement.

    [Deleted User]
  • rodaroda Posts: 73 Baller
    My '05 MCX did the same thing. Pulled them and had an aluminum airboat shop install new aluminum plugs in all locations. They cut the plugs from aluminum stock.

    A neighbors '06 MCX had same issue, I cut an aluminum disk the size of a quarter and used JB weld putty to hold it in place. It has held for almost a year now without issue.
  • Thanks to you all.

    The site that I've found cast iron manifolds the least expensive is yet it's still a good chunk of change that I'd rather put to something like a new ski. I believe i can find a place to weld in the new caps and feel that this would ultimately be a lot less expensive.

    My follow up question is this: does it make sense to have the newly welded manifolds to be painted or powder coated? That should then prevent any kind of corrosion. Or would this be a bad thing for some reason?
  • RichardDoaneRichardDoane Posts: 3,973 Mega Baller
    powder coating rocks over spray paint everytime
    BallOfSpray Pacific Northwest Vice President of Event Management, aka "Zappy"
    [Deleted User]
  • macmac Posts: 60 Baller
    I had the same issue/'05 MC MCX engine; I took the exhaust manifolds to a TIG welder, had all the plugs replaced, sandblasted inside and out and powered coated for $180...looks like new...mac
  • skiannaskianna Posts: 1 Baller
    I have the same issue/04 MC 197, MCX engine; no visible corrosion, but one of the anodes started leaking, luckily on my last ski day of the season last Nov. Trying to decide best course of action.
  • RynoRyno Posts: 252 Baller
    edited January 2012
    Same deal happened with my old mans 04' Malibu LXi. We cutout the caps and replaced them with new alloy ones. However at the end of the day these engines have been designed for cars, and as such are not sufficiently marinized to handle a life in and out of the water.

    The best protection you can do is flush the boat every time you finish up for the day. Ensure the boat has been run long enough for the thermostats to open, then put a dose of "Macs" through the engine.

    The local river I ski at is semi salt, with a large ski/caravan park on it. Over the last summer we had 4 Malibu's go pop due to corrosion.

    Obviously your engine will last a lot longer if it's used in only fresh water. But if it's in salt and you're not flushing it properly, you'll be lucky to get more than two seasons out of a set of manifolds (let alone the damage it's doing to the rest of the engine).
    Ryan McGill - South Coast, New South Wales, Australia
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