Exhaust Manifold Service Life

JimS123

JimS123

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I was reading the Q&A column in a major boating magazine and was surprised by the answer from their reputed "expert". The question was regarding loose bolts on an exhaust manifold of a 1970 3 Liter stern drive.

The "answer" said that ....quote..."exhaust manifoilds are good for 6 years, 8 tops, fewer in salt water".

I won't argue the salt water issue, but my thinking is that a cast iron manifold should last many, many years in a fresh water environment.

Comments from the long time mechanics?
 
Don S

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Re: Exhaust Manifold Service Life

Fresh water cooled engines that never see salt water seldom fail, let alone in 6 to 8 years. The problem with a lot of the "Experts" that write articles for magazines, is that they are writers, not mechanics. Or the mechanic that talked to the writer had all his information edited by an editor that's even worse on the subject.

6-8 years in salt water is pretty close. But with flushing and using something like Salt-Away when flushing can even increase that on trailer boats.
 
Bondo

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Re: Exhaust Manifold Service Life

JimS123 said:
I was reading the Q&A column in a major boating magazine and was surprised by the answer from their reputed "expert". The question was regarding loose bolts on an exhaust manifold of a 1970 3 Liter stern drive.

The "answer" said that ....quote..."exhaust manifoilds are good for 6 years, 8 tops, fewer in salt water".

I won't argue the salt water issue, but my thinking is that a cast iron manifold should last many, many years in a fresh water environment.

Comments from the long time mechanics?
Click to expand...

Ayuh,.... Up here on the Sweetwater seas,... manifolds freeze, 'n split from not bein' drained,....

I've never seen any rot out, Ever....
40 years is common....

The notorious 1 pc. "Batwings" used on V6s by Merc, 'n OMC, I've seen ruinin' many a motor though...
 
Don S

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Re: Exhaust Manifold Service Life

The notorious 1 pc. "Batwings" used on V6s by Merc, 'n OMC, I've seen ruinin' many a motor though...
Click to expand...

Are you sure they didn't freeze? They are made out of the same cast iron as the 2 piece setup. Don't see why they should fail any quicker.
 
Bondo

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Re: Exhaust Manifold Service Life

Don S said:
Are you sure they didn't freeze? They are made out of the same cast iron as the 2 piece setup. Don't see why they should fail any quicker.
Click to expand...

Ayuh,... Nope,... Not sure of anything, not under My care,....

I which I coulda gotten my hands on a set off any of the motors I've seen it happen to, but couldn't...

I've heard the internet myth that core shift in the castin' process is the Issue,...

I know these motors up, 'n hydro-locked, mid-season, 'n trashed the motors...

I'd love to take a BFHammer to a bad 1, 'n See, exactly why they're failin'....
 
Don S

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Re: Exhaust Manifold Service Life

Having spent 12 years working in a SS foundry, trust me, core shift is real, and it happens. The bigger the core (one piece manifolds) the more things move and one side becomes thicker and the other thinner when they move.

I'd love to take a BFHammer to a bad 1, 'n See, exactly why they're failin'....
Click to expand...

I would rather take a saw and a camera to a 1 piece manifold distruction.
 
JimS123

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Re: Exhaust Manifold Service Life

Don S said:
Fresh water cooled engines that never see salt water seldom fail, let alone in 6 to 8 years. The problem with a lot of the "Experts" that write articles for magazines, is that they are writers, not mechanics. Or the mechanic that talked to the writer had all his information edited by an editor that's even worse on the subject.

6-8 years in salt water is pretty close. But with flushing and using something like Salt-Away when flushing can even increase that on trailer boats.
Click to expand...

That's kinda what I figured, but the column has no option to reply, so I couldn't question the response.

Usually, the answers are spot on. This was an unusual reply in my mind.

Thanks to all for the responses...
 
Bondo

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Re: Exhaust Manifold Service Life

I was reading the Q&A column in a major boating magazine and was surprised by the answer from their reputed "expert".
Click to expand...
JimS123 said:
That's kinda what I figured, but the column has no option to reply, so I couldn't question the response.

Usually, the answers are spot on. This was an unusual reply in my mind.

Thanks to all for the responses...
Click to expand...

Ayuh,..... Has that major boatin' mag, got a website,..??

I challenged 1 of those fellas spoutin' poo, 'n bad facts once on that major boatin' mag's website....

he backpeddled, stuttered, 'n sputtered something 'bout bein' an Outboard expert, 'n not an I/O guy....
So he Guessed at the gear ratios...

Was yer guy named Grid,..??
 
Friscoboater

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Re: Exhaust Manifold Service Life

That is good to know about the manifolds. I always heard even in fresh water you needed to replace them every 6 years.
 
Don S

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Re: Exhaust Manifold Service Life

friscoboater said:
That is good to know about the manifolds. I always heard even in fresh water you needed to replace them every 6 years.
Click to expand...

Isn't the internet and the "Experts" wonderful at times. :facepalm:

Just think of all the poor fresh water boaters out there that never "Heard" that and they have been using the same manifolds and elbows for 20 or 30 years with no problem. Bet if you pulled their elbows off you would find everything is still in perfectly usable condition.

Now, how do you know what I am saying is true? LOL, yeah, that's the problem, you don't.
 
Lou C

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Re: Exhaust Manifold Service Life

OMC manifold change 6-2011.jpgomc manifolds.jpgWell Bondo I've been using the OMC batwings (I have 2 sets) in salt water, used the first set 5 seasons, on the second set now and NEVER had ANY water in the engine, I pull the plugs every spring to replace em and there has never been signs of water intrusion. I for one feel the one piece design is superior to the standard 2 piece design in salt water. That joint eventually leaks and that is what rusts exhaust valve stems. Here is a pic of when I changed them the last time in 2010, look at the valve stems, this engine had been used in salt water at least 10 years if not more at that point.....Here is a pic of the old vs new manifolds, as you can see one port clogged but it was easily unclogged. I still installed the new ones to be on the safe side. If I could still get these, I'd use them for sure.
 
Friscoboater

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Re: Exhaust Manifold Service Life

Don S said:
Isn't the internet and the "Experts" wonderful at times. :facepalm:

Just think of all the poor fresh water boaters out there that never "Heard" that and they have been using the same manifolds and elbows for 20 or 30 years with no problem. Bet if you pulled their elbows off you would find everything is still in perfectly usable condition.

Now, how do you know what I am saying is true? LOL, yeah, that's the problem, you don't.
Click to expand...

Very True! LOL.
 
JimS123

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Re: Exhaust Manifold Service Life

Bond-o said:
Ayuh,..... Has that major boatin' mag, got a website,..??

I challenged 1 of those fellas spoutin' poo, 'n bad facts once on that major boatin' mag's website....

he backpeddled, stuttered, 'n sputtered something 'bout bein' an Outboard expert, 'n not an I/O guy....
So he Guessed at the gear ratios...

Was yer guy named Grid,..??
Click to expand...

No a different name. They do have a web site, but no links to the Q&A column. If they had one I would have replied back to them.
 
90stingray

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Re: Exhaust Manifold Service Life

OP, when i owned my 1990 Stingray, I had heard that manifolds were time limited too. I got a little worried as the 4.3's manifolds were originals. Instead of trusting the internet and just buying new, I decided i should remove them and inspect and to my surprise, they looked fine. They were over 20 years old BUT only had 300 hours of use. Reassembled with new gaskets and good to go!

Bond-o said:
The notorious 1 pc. "Batwings" used on V6s by Merc, 'n OMC, I've seen ruinin' many a motor though...
Click to expand...

I have heard that as well... and it makes you wonder why Merc only ran them for what, 3 years? My boat, unfortunately came with those 1 piece units. Just to make me sleep better at night, I changed out the manifolds last year to the "older" style manifold, riser, and elbow. I know the dry joint are a superior design... but hell my old boat made it 20+ years. That will be more than fine for me :)
 
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