Aluminum exhaust manifold vs cast iron

[fmalott]

i was told that aluminum is the better choice to extend life of motor 1983 470 merc the cast iron cracks and leaks in cylinder is this a common problem for this motor? i was looking on ebay for prices found one for $400 the item said "riser must have long bolts to fit manifold can be used to replace cast iron model but will require long bolt style elbow available in our store" can some one explain why different bolts and what does it mean elbow
THANKS for everybodys patients i want to learn every inch of this motor

 

[Roman S]

Re: Aluminum exhaust manifold vs cast iron

If you run your boat in fresh or sweetwater, good aluminum exhaust manifolds save you some weight. The more expensive solutions have engineered individual runners. In salt water, they are a bit more dubious. Also, I don't know whether there is aluminum manifold for your application. If you do a search, you get more info.
RS

 

[fmalott]

Re: Aluminum exhaust manifold vs cast iron

thanks for advice roman i'm not concerned about weight i can find manifolds no problem but your response does not answer my question

 

[zbnutcase]

Re: Aluminum exhaust manifold vs cast iron

Yes the aluminum one is the one to have, but you have to use the matching elbow (and bolts) because when they switched to aluminum, the elbow became the expansion tank. Older ones had the tank at the front of the manifold. The elbow, AKA riser, is the part that connects the manifold to the exhaust tube; it is also where the cooling water(raw water side) exiting the engine mixes with the exhaust gases. And on these engines with aluminum manifold, it is also the coolant (anti-freeze side) expansion tank, hence the radiator cap on it.

 

[fmalott]

Re: Aluminum exhaust manifold vs cast iron

ok i'm understanding a lot more now thanks zbnutcase one last thing is it a common problem with cast iron manifold to crack or is it just every blue moon and not worry and just inspect regularly

 

[zbnutcase]

Re: Aluminum exhaust manifold vs cast iron

Not a problem I am aware of on these engines, as they are full of anti-freeze, unlike the vast majority of other marine engines which are full of sea water, and they crack all the time in freezing weather,maybe thats what your thinking of?

 

[fmalott]

Re: Aluminum exhaust manifold vs cast iron

no just under normal use do they crack more often then not

 

[spdracr39]

Re: Aluminum exhaust manifold vs cast iron

No, they don't.

 

[fmalott]

Re: Aluminum exhaust manifold vs cast iron

let say it does crack what would replace with cast iron or aluminum which ever is cheaper i guess

 

[rodbolt]

Re: Aluminum exhaust manifold vs cast iron

yes cast iron ones DID crack and DID leak coolent into the manifold and usually took out #4 cyl.
along with a head gasket due to the over heat.
thats why merc dropped the cast iron one and only offered the AL one as a kit form to replace the buggery cast iron ones.
had nothing to do with freezing.
last kit I bought from merc was just over 700 dollars and about 1997.
its also why now I refuse to work on 3.7 motors but will relate anything I remember.
good thing nightmares fade fast.

 

[fmalott]

Re: Aluminum exhaust manifold vs cast iron

then do i have anything to worry about meaning it will then crack and i will have to replace or is there any chance it will not crack there's got to be some that did not crack

 

[rodbolt]

Re: Aluminum exhaust manifold vs cast iron

not ALL did,not ALL vegas rusted away.
if its not cracked now run it.
when it cracks first thing you notice is a slight rise in operating temps, a graysish smoke at idle, a light miss at idle and if you lean over the trasom you will smell that sickly sweet smell of hot antifreze.
I dunno why they crack, maybe the same reason the inline 6 manifolds had a tendancy to crack internally.
the 2.5 and 3.0 inlines have been known to do it as well.

 

[fmalott]

Re: Aluminum exhaust manifold vs cast iron

thanks rodbolt i will save this post so i know what to look for and smell for, do the aluminum ones crack at all or what problem do they tend to have

 

[zbnutcase]

Re: Aluminum exhaust manifold vs cast iron

Aluminum ones are pretty much bulletproof-the iron ones mostly too, any manifold can crack given the right conditions...

 

[fmalott]

Re: Aluminum exhaust manifold vs cast iron

so to make a long question short keep your eye on the motor and signs of running bad and keep fingers crossed