1999 7.4 MPI Exhaust manifolds

[earnies2]

the boat has 160 hrs on it the manifolds are original the boat has never been in salt water only fresh water. how do you tell whan it is time to change the manifolds? is their some signs to look for or test to do to check the manifolds. and if i do replace them should i usr cast iron or alumium?8)

 

[bruceb58]

Re: 1999 7.4 MPI Exhaust manifolds

If you only use the boat in fresh water then the manifolds will last a very long time...more than likely, you will never have to replace them.

 

[Bondo]

Re: 1999 7.4 MPI Exhaust manifolds

Ayuh,...... Up here in the Sweetwater,......
30 Years and still going Strong is Common.......

 

[earnies2]

Re: 1999 7.4 MPI Exhaust manifolds

Ok that's good to know but how do you tell whan it is time to change the manifolds? is their some signs to look for or test to do to check the manifolds. and if i do replace them should i use cast iron or alumium?

 

[rodbolt]

Re: 1999 7.4 MPI Exhaust manifolds

normally its when either the risers clog and start heating up or the engine idles funny and a spark plug inspection indicates a water burn.
in fresh water the iron seems to last a long time.
as far as iron or AL it depends on the originals.
over the years merc has used a lot of materiel/styles on manifolds,cooling systems and materiels.
in my area 3 years is not uncommon for failure.
I have a PCM 8.1 out of the hull now that actually rusted a hole through an exhast runner and was blasting gases hot enough to melt 2 plug wires and the port front motor mount, engine was installed new in 03.
in fact barring a rainout reinstalling it is todays project, or at least it was when I left yesterday .