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2006 Horizon 8.1 exhaust manifold lifespan

O

outobie

Regular Contributor
Hello Guys:

I'd like to get your thoughts on my manifolds.

I just bought a new to me boat with 2006 Mercruiser Horizon 8.1 V-Drives with 750 hours. the elbows and exhaust manifolds are Originals, now 13 years old.

I bought the boat from the original owner who lift kept the boat it's entire life in the middle of the Chesapeake Bay (brackish water).
with the engines being Fresh Water Cooled and the Elbows being Stainless with Cast Iron manifolds, do I still need to worry about them?

what is the recommended way to care for them? Is there any raw water run through the manifolds on these? do I need to inspect them or replace them with some specific interval?

everything has been maintained by the book with receipts for regular maintenance but there is nothing for the manifolds in the service schedule that I can find. the engines run perfect and I'd like to keep them that way

thanks
 
Last edited:
There are full and partial FW systems out there. In the full systems, the exhaust manifolds have anti freeze in them.
I got over 6 seasons on a pair of MERC dryjoint elbows (raw water cooled) on a full system kept in Barnegat Bay by flushing the raw water system with tap water every couple of trips, and monthly and end of season with saltaway. They were still in great shape when I pulled them.

I have a "T" right after my thruhull pickup for flushing.
 
The Mercruiser 8.1 is not available in a full cooling system. If the Iron manifolds are 13 years old I would change them. Cheaper to replace the manifolds then to replace the long block.
 
Thanks Chirs:

I'm leaning towards changing them for piece of Mind but I'd love to see an actual schedule or inspection. is there any maintenance schedule from Mercury about exhaust manifolds?

also what about the elbows? the Elbows are stainless so I'm assuming they are ok?
 
Don't know about Mercury schedule but I think most folks inspect every 3-5 years depending on how aggressive the water your boating in is. Stainless should be ok for the elbows
 
outobie said:
Thanks Chirs:

I'm leaning towards changing them for piece of Mind but I'd love to see an actual schedule or inspection. is there any maintenance schedule from Mercury about exhaust manifolds?

also what about the elbows? the Elbows are stainless so I'm assuming they are ok?
Click to expand...

Elbows are stainless.... When the Manifolds are 8-10 years old I change them.
 
alright I'll be adding those to my winter maintenance list.

to double check my memory. manifolds come with the mating surfaces painted.

- I should block sand the paint off to get to smooth clean bare metal mating surfaces before mounting
- manifold gaskets are installed dry (no Mercury perfect seal?)
- all mounting bolts get coated with Perfect seal (not locktight or antisieze)
- for the heat exchangers I know I replace the gaskets on the end caps, but how do I clean them out? my other boats have been raw water cooled.

for the rest of my winter service to make sure the motors are fully up to date on maintenance, I'll replace:
- all rubber hoses,
- thermostat and
- drive belts while I'm in there along with
- plugs,
- plug wires,
- fuel filters and
- clean the flame arrestor.
- change the oil & filter
- change the transmission oil and filter
- what am I missing?

do I need to mess with the lift mufflers? (these are Vdrives not sterndrives)

thanks
 
outobie said:
alright I'll be adding those to my winter maintenance list.

to double check my memory. manifolds come with the mating surfaces painted.

- I should block sand the paint off to get to smooth clean bare metal mating surfaces before mounting
- manifold gaskets are installed dry (no Mercury perfect seal?)
- all mounting bolts get coated with Perfect seal (not locktight or antisieze)
- for the heat exchangers I know I replace the gaskets on the end caps, but how do I clean them out? my other boats have been raw water cooled.

for the rest of my winter service to make sure the motors are fully up to date on maintenance, I'll replace:
- all rubber hoses,
- thermostat and
- drive belts while I'm in there along with
- plugs,
- plug wires,
- fuel filters and
- clean the flame arrestor.
- change the oil & filter
- change the transmission oil and filter
- what am I missing?

do I need to mess with the lift mufflers? (these are Vdrives not sterndrives)

thanks
Click to expand...

re: "to double check my memory. manifolds come with the mating surfaces painted. "

On my OEM replacement dry joint elbows, Merc did not mask the threads on the tapped holes for the water feed. I'm assuming they don't for the feed on the manifold either. It was a VERY tiresome job for me to clear these threads so that the brass fittings (water feed nipple) would seat properly since I did not have the correct size tap (nor could I find one locally) to clear the threads.

re: "- for the heat exchangers I know I replace the gaskets on the end caps, but how do I clean them out? my other boats have been raw water cooled."

On my boat at least, my routine fresh water flushes and occasional saltaway treatment have kept them clear.
 
Last edited:
outobie said:
alright I'll be adding those to my winter maintenance list.

to double check my memory. manifolds come with the mating surfaces painted.

- I should block sand the paint off to get to smooth clean bare metal mating surfaces before mounting
- manifold gaskets are installed dry (no Mercury perfect seal?)
- all mounting bolts get coated with Perfect seal (not locktight or antisieze)
- for the heat exchangers I know I replace the gaskets on the end caps, but how do I clean them out? my other boats have been raw water cooled.

for the rest of my winter service to make sure the motors are fully up to date on maintenance, I'll replace:
- all rubber hoses,
- thermostat and
- drive belts while I'm in there along with
- plugs,
- plug wires,
- fuel filters and
- clean the flame arrestor.
- change the oil & filter
- change the transmission oil and filter
- what am I missing?

do I need to mess with the lift mufflers? (these are Vdrives not sterndrives)

thanks
Click to expand...

Leave the paint. No sealer.

Leave the hoses unless they are dry.
 
just to follow up on this. I replaced my manifolds with new OEM Mercruiser ones. the old ones looked damned near perfect. it didn't seem worth it to save them or sell them but if I hadn't already bought the new ones I wouldn't have bothered to replace them.

I was told by the original owner that he never replaced the manifolds since 2006 and with 700 hours lift kept on the Chesapeake (solomon's Island)...so after 14 years in brackish water the manifolds looked very good. the Stainless elbows I reused as they were perfect. I wouldn't expect these manifolds to ever need replacing again for the life of the motor so long as it stays in the brackish waters of the chesapeake.
 
outobie said:
just to follow up on this. I replaced my manifolds with new OEM Mercruiser ones. the old ones looked damned near perfect. it didn't seem worth it to save them or sell them but if I hadn't already bought the new ones I wouldn't have bothered to replace them.

I was told by the original owner that he never replaced the manifolds since 2006 and with 700 hours lift kept on the Chesapeake (solomon's Island)...so after 14 years in brackish water the manifolds looked very good. the Stainless elbows I reused as they were perfect. I wouldn't expect these manifolds to ever need replacing again for the life of the motor so long as it stays in the brackish waters of the chesapeake.
Click to expand...

Cheaper than a new engine... Were the old manifolds Iron or Aluminum?
 
Iron...I think the Aluminum ones were discontinued a few years earlier.

I'm glad I changed them and would do it again...but I don't believe I needed to...it's more for piece of mind rather than actual need
 
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