2012 Merc V-6 I/O cat converter exhaust question...

[Lou C]

I've got a friend with a 2012 Merc V6 I/O with the cat converter exhaust. Used in salt water just like out boat, moored approx. 6 month season. Their mechanic is advising replacing the manifolds and elbows as it typically done here with cast iron exhaust every 5-7 years. The cost parts and labor is approx. $4500. I was not able to find Merc OE pricing on these units, only on V/P units and the parts are indeed expensive. But I don't know if they are made of cast iron or aluminum and if they last the same or longer as cast iron in our environment. Thoughts? Suggestions?

They asked me if I'd get another boat with I/O and cat exhaust and of course my answer is NO WAY. At those parts prices then outboards start to really make more sense here.

 

[alldodge]

Unable to say for sure, but always thought the CAT motors are closed cooled. If they are closed cooled then only the elbows would need replacing. The elbow alone is from $750 to $1200 for both (item 7) depends on how much rise is needed

https://www.mercruiserparts.com/bam/subassembly/31527/16591/110

Personally, don't think I'll ever on a CAT motor, so no new ones for me. Also the outboards have CAT's now

 

[Lou C]

Where have you seen cats on outboards? There was talk of this insanity on outboards but its not reality yet. Let's start with how O2 sensors do not like a wet environment and go to the high temps of Catalysts in a closed engine compartment that depend on water cooling.
Thanks for the link to parts prices, I'll pass that along to them so they can judge if the repair cost is fair.

 

[Lou C]

PS for a good laugh I looked at engine parts prices (Merc's 4.5 V6) which looks awfully suspiciously like a slightly modified GM V6. $6 grand for a long block. Ridiculous as are the individual parts prices. This nonsense will spell the end for sterndrives. Priced out of the market with no advantages left but closed cooling. And all the built in disadvantages of sterndrives with a big new one (Cat Converter $$$ exhaust)!

 

[muc]

(Merc's 4.5 V6) which looks awfully suspiciously like a slightly modified GM V6.

Iv'e been told by MerCruiser that they don't source any parts from GM for this engine.

 

[Bt Doctur]

could pick up a nice 6.2 for that much

 

[Lou C]

Iv'e been told by MerCruiser that they don't source any parts from GM for this engine.

Well if they don't it is surely very similar in design to the GM V6. As in, still has a 90* included angle between the cyls, so it still has the need for the same balance shaft as GM used, and actually other than some differences in the head castings and block, it looks like they bought the design from GM. Even the spacing of the exhaust/intake ports in the cyl heads, the roller lifters and the parts that keep them aligned, it all looks very similar. But what they charge for parts, will drive smart people to outboards I think unless they just must have a sterndrive boat.

If Merc was designing their own inboard V6, you would think they would have designed it from the ground up to use a 60* included angle between the cyl banks, as every other modern V6 has. The GM 4.3 like the Buick 3.8 were made by removing 2 cyls from a V8 design which creates balance problems. They modified the crank to alleviate some of this but adding the balance shaft smoothed it out a good bit more. The old 4.3 is 3/4ths of a 5.7 with the same bore and stroke.

 

[Scott Danforth]

while it is a Mercruiser built motor, it is also modeled after the GM motor to an extent. including keeping the GM bolt pattern on the crank and the flywheel.

 

[Lou C]

Did they just wait for the patents to run out, build it in house and make all the parts 3 x as expensive as GM?