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Exhaust manifold


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I have a small hole in my exhaust manifold that is leaking water. Since the season is short here in Mass I was going to just repair the hole and replace the manifold in the spring ( $900 for a new one ) Any suggestions on what to use?

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1 hour ago, JasonK said:

A friend told me running with a leaky manifold can cause a valve seat to drop. At least he thinks that's why his did.

I'm not sure how that makes any sense.  It could potentially cause the engine to overheat, and the bilge to fill up with water, but it would be tough to miss long before either of those happened.  

Not sure what the point of those thin, round areas are on those manifolds, but eventually they spring leaks there.  My buddy has those manifolds on his 2005 Response.  He has patched them with J.B. Weld.

(If replacements are $900 each, I'm assuming you have the newer style, one-piece manifold.)

Edited by powbmps
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2 hours ago, srdd455 said:

I have a small hole in my exhaust manifold that is leaking water. Since the season is short here in Mass I was going to just repair the hole and replace the manifold in the spring ( $900 for a new one ) Any suggestions on what to use?

If you have the aluminum manifolds and one of the core plugs is leaking, you can get those fixed.  I bought a used set that were leaking (and had several leaks fixed with JB weld).  Had all new core plugs, on both manifolds, welded in for $100.  I used .100" thick aluminum, which I think is about twice as thick as the original.

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7 minutes ago, MadMan said:

If you have the aluminum manifolds and one of the core plugs is leaking, you can get those fixed.  I bought a used set that were leaking (and had several leaks fixed with JB weld).  Had all new core plugs, on both manifolds, welded in for $100.  I used .100" thick aluminum, which I think is about twice as thick as the original.

MadMan,

Minor hijack, but any idea what the benefits of that manifold style is?  As far as I can tell, they are the only difference between the 2003 Monsoon 335 and the 2004 Monsoon 340.  $900 each vs. $250 each (above the 2003 style) is pretty steep for 5 hp.  Weight savings maybe?

Edited by powbmps
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3 minutes ago, powbmps said:

MadMan,

Minor hijack, but any idea what the benefits of that manifold style is?  As far as I can tell, they are the only difference between the 2003 Monsoon 335 and the 2004 Monsoon 340.  $900 each vs. $250 each (above the 2003 style) is pretty steep for 5 hp.  Weight savings maybe?

I agree, it's not much bang for the buck horsepower wise.  And, depending on what you use your boat for, less weight might be a negative.

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It was leaking (on the outside as far as he could tell) after he didn't drain it for winter. Ran it for the next summer before changing it. He believed either the water running down the outside on to the head, or an internal leak causing a cool spot on the head. It was a very small leak.

Any other guess why his valve seat dropped, at 900 hours, after that summer? Cross out surfing listed. He didn't surf. 1989 Mercruiser motor.

Where is the hole at that's leaking in the OP's post?

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I'd at the very least take the risers off (just buy a couple of new gaskets which are cheap) and inspect what's going on.  At least you can tell the health of the manifolds.  If there is any evidence that there is perforation through the inner jacket you really have to replace.  Otherwise you are rolling the dice on a much more expensive bill... just sayin....

Edited by solorex
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2 hours ago, powbmps said:

I'm not sure how that makes any sense.  It could potentially cause the engine to overheat, and the bilge to fill up with water, but it would be tough to miss long before either of those happened.  

Not sure what the point of those thin, round areas are on those manifolds, but eventually they spring leaks there.  My buddy has those manifolds on his 2005 Response.  He has patched them with J.B. Weld.

(If replacements are $900 each, I'm assuming you have the newer style, one-piece manifold.)

I do have the one piece. I will try the JB weld

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@srdd455:  You should be able to salvage the manifold at least short term with JB Weld.  I highly suggest you remove and inspect for any inner leakage so you don't end up with water in the cylinder.  That would happen after you shut off the engine during the cooling cycle.  If you have noticed any hard starts, that may be a clue that there is some inner leakage.

@powbmps:  The aluminum one piece manifolds offer a couple of advantages,  significantly lighter weight (if that is what you are after) and improved exhaust scavenging.  The old open chamber cast iron manifolds are not very efficient when it comes to exhaust scavenging, hence the trend as the HP war heated up, to improve the flow path.  One item to watch, expansion rates between aluminum and cast iron are very different, that 'exercises' the manifold gasket leading to quicker wear.  Another advantage, aluminum manifolds run much cooler than cast iron, as in no issue to lay your hand on the manifold when hot.

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