Manifold corrosion in 340 engine

[seawinder]

Have other owners of Indmar monsoon 340 engines had problems with corrosion of the aluminum exhaust manifolds? I could't figure out where all that water in the bilge was coming from at the end of this season in my 2004 boat, and why the bilge pump kept running.... Until i had the boat in the shop to winterize and spotted a leak from one of the plugs used to cast the aluminum manifold. According to the dealer, a number of owners have had to replace the aluminum manifolds with the heavier cast iron ones that are less prone to corrosion in brackish water. Of course the boat was under warranty when the leaks occured, but not when i discovered it so I'm on my own for the labor to change this, although indmar did send the the cast iron manifolds in exchange for the leaky ones. The guy at Indmar acted like they were doing me a big favor and seemed happy it was reported one month out of warranty. I removed the leaking manifold. Of the nine welded plugs in the casting, more than half were showing peeling paint with corrosion almost all the way thru. two were leaking thru pinholes in the center of corrosion. Naturally these leaks were in spots that were hardest to see when the boat was running.

I can weld these back up with my tig welder and started to do so, but i"m afraid it will leak again in two years or so, and i already had to send the starter out to be rebuilt cause it got wet. So I guess i will have to go with the cast iron. They arrived today, with new bolts and gaskets and hose fittings. But one question i have is that that i have to drill and tap the holes for the fittings in each manifold. There appears to be a similar hole that could be drilled in the riser for a fitting as well, but I have no reason to do so if there is nothing to hook up to it.

Has anyone else been thru this process? Is there going to be any noticable power drop? I don't mind the extra weight.

[bigD]

No problems so far, I ALWAYS flush the engine after the Deltas brackish water, and occasionally I flush the engine just because it's going to sit for a while. Maybe it saved me.

[99response]

You may loose 5 HP. In 03 the monsoon was 335 hp, in 04 they went to the EXT exhaust and went up to 340 hp. I'd be shocked if you notice.

As for drilling and tapping the manifolds? I'm pretty suprised you'd have to do that. Also Indmar doesn't use gaskets on exhaust manifolds just that great stuff.

Chris

[JAGMAN]

I run in brackish water too. I haven't noticed any problems, but after reading this post I will look much more closely at the ETX manifolds.

That said, did you flush after each session? I just want to know what I can expect.

[99response]

I believe the problem with these manifolds was they were using a different metal to fill the casting holes, which caused galvanic corrosion which is exacerbated in salt/brackish water use.

Hopefully they've resolved the problem but not sure how long ago they relized it.

-Chris

[electricjohn]

Makes me glad I only have the 335 hp version.

[SacRiverRat]

Yea... figure I'm even safer with the '02 325hp version

[Hman442]

Yea... figure I'm even safer with the '02 325hp version

[seawinder]

I completed the job of replacing those manifolds...i did not have to drill holes, the job went pretty smoothly. manifolds bolt to heads, then the riser bolts to the manifold with a gasket.

the dealer here on the chesapeake tells me they have replaced at least ten of these. I don't hnow how many were warrranty jobs and how many not. so if you are close to the warranty expiration date, look closely at those manifolds, both sides, facing out and facing the engine. there are nine plugs welded. if you see any of the black paint lifting off the center, there is corrosion underneath...beware, once the paint bubbles off, you can poke thru pretty easily . the manifolds have been changed on the new version of the engine so this dissimilar metal problem in the welds/plugs no longer an issue. more diligent flushing may have delayed this problem for me but some of those who had this problem say they "flushed after every use'. thanks to those who responded

[Chaabo]

http://www.themalibucrew.com/forums/index.php?showtopic=6436

Unfortunately the pics have been removed.

But that is (was?) a common problem.

[JAGMAN]

Thanks to Seawinder for posting this thread. I was winterizing today and decided to look for corrosion around the welded plugs on the ETX manifolds. I had one spot that had pealing paint. Scraped it away, and sure enough water was leaking out of it. I've got 7 months left on the warranty, and hope that the dealer will replace both manifolds with new ones (even though only one is leaking).

This whole thread makes me wonder, the Indmar manual specifically states that the ETX manifolds are very corrosion resistant and should out last traditional two-piece manifolds. I hope that if the dealer does replace the manifolds and that the new ones don't have dissimilar metals for the casting and the plugs...

I do run in brackish water (~1/7th the salinity of saltwater), but have religiously flushed after every use. Have a Flush-Pro, and closed-cooling.

I wonder if there is a way to go to a fully closed cooling system, rather than a half system like I have now?

[99response]

If you flush every time and already have closed cooling, manifolds should last awhile and you should not have to upgrade to a fully closed system. Have the dealer warranty the EXT's and see what happens. Worst case they last another 3 years then you go to cast iron ones.

-Chris

[MoonDawg]

That is too bad about the ETX manifolds... You can replace your ETX manifolds with new ETX's but they are costly... around $2500 for the set. If that happened to me I would replace the manifolds with EMI Thunder stainless $1800

Edited December 4, 2007 by MoonDawg

[JAGMAN]

That is too bad about the ETX manifolds... You can replace your ETX manifolds with new ETX's but they are costly... around $2500 for the set. If that happened to me I would replace the manifolds with EMI Thunder stainless $1800

Since I am still under warranty, I am going to have the dealer (assuming they see things the way I do) replace the old ETX's with new ETX's and hope for the best. Best case, they've fixed the ETX's so i won't happen again; Worst case, when the new ETX's fail replace them with cast iron.

The point at which the failure occurred was the center of of the welded plugs, where there was a pinhole. I think it was caused by the wrong choice of metal, and the fact that there is a thin spot on the center of each plug.

EDIT: OBTW, this is not the first boat I've had in this environment. The last one I had had cast iron exhaust manifolds and is at 12 years and counting on the original manifolds. This ETX failure does not bode well for Fresh Water ETX users either. By my calculations Fresh water only ETX will likely have a ~5 year failure point if they suffer from the same galvanic issues at the welded plugs.

If I had to replace these on my own I would do it myself, and grind out the old freeze plugs, and weld in new ones made of a different material.

Edited December 4, 2007 by JAGMAN

[Woodski]

Other options on replacement manifolds include Stainless Marine, Eddie Marine and Hardin. All three make aluminum replacement exhaust manifolds. The upside is that they are quite light, removing a paltry 90 #, nice gain for slalomers and footers. I have found they do require a bit more attention in watching the gaskets, but they do run a lot cooler than cast iron ones. Also, they all tend to have runners built in as compared to the big chamber of the cast version, therefore offer an increase in performance. They are very popular for the big block GM engines, mostly used by the off shore crowd.

[BlastRlxi]

Other options on replacement manifolds include Stainless Marine, Eddie Marine and Hardin. All three make aluminum replacement exhaust manifolds. The upside is that they are quite light, removing a paltry 90 #, nice gain for slalomers and footers. I have found they do require a bit more attention in watching the gaskets, but they do run a lot cooler than cast iron ones. Also, they all tend to have runners built in as compared to the big chamber of the cast version, therefore offer an increase in performance. They are very popular for the big block GM engines, mostly used by the off shore crowd.

Will they fit under the engine cover on a DD or VD without modification?

[Woodski]

Yes, most are no larger than the cast ones you currently have and all the ones I have seen will fit under the enigine cover. I installed a set of Stainless Marine units and a larger exhaust system to complement the larger diameter secondary elbow.

[Gordo]

So, my 2004 VLX 340hp Monsoon has aluminum exhaust manifolds? I have always run in fresh water, but, reading this thread, it sounds like its a matter of time? Dang - guess I need to check my Bu out - she's taking her winter nap, but it might be warm enough to get on the lake here this weekend.

[MoonDawg]

So, my 2004 VLX 340hp Monsoon has aluminum exhaust manifolds? I have always run in fresh water, but, reading this thread, it sounds like its a matter of time? Dang - guess I need to check my Bu out - she's taking her winter nap, but it might be warm enough to get on the lake here this weekend.

My kids are doing the snow dance tonight so they don't have to go to school tomorrow... The weather service has forecast our first winter storm watch (1-4 inches) tonight... my season is done for.

[jphillips]

Your lucky... my boat was parked a month ago, right beside the skating rink... which is now about 2 or 3 days away from being ready for its first skate.

[Gordo]

I looked at my manifolds on my 2004 VLX. They sure dont "feel" like they are aluminum....more ike they are cast iron. Maybe this is just "hoping"? Who can confrim that my manifolds are aluminum??

[MoonDawg]

Gordo,

Here is a stock aluminum manifold. An early ETX without catalytic converter.

I dream of my 96 monsoon looking like that :-)

[doughickey]

Your lucky... my boat was parked a month ago, right beside the skating rink... which is now about 2 or 3 days away from being ready for its first skate.

Does Malibu warranty windshields for puck damage? Would your insurance cover the following comprehensive claim "Windshield of ski boat shattered by flying puck"? May raise a few eyebrows.

Might wanna move that boat a bit further away next year.

[jphillips]

Thought it all through... The boat is at center ice and about 20' away with the back of the boat facing the rink, which it has boards all around it. While I get to use the farmers field I try to stay in the area behind my house. We kind of figure any fly pucks over that way should be tips and should really have no force in them.

[Gordo]

Gordo,

Here is a stock aluminum manifold. An early ETX without catalytic converter.

I dream of my 96 monsoon looking like that :-)

Well, thank goodness my manifolds don't look like that (although those are darn good looking!). Mine are painted black. And they are not designed like that at all - pretty traditional "car" looking exhaust headers. It never crossed my mind that they could be anything but cast iron the way they look.

Edited December 13, 2007 by Gordo