Twin Merc. 6.2 Mags with Bravo 3 - EMCT Temperature Overheat Fault - Port side Manifolds (Only)

[Ploring]

Hi all, I've been reading threads like this vigorously trying to figure out if I need to replace my exhaust (and potentially my CATS) -- I have a 2013 Monterey SY 340 with twin Merc 377 Mags EC - with PCM 555 control modules.
SERIAL NUMBER(S):
Port; 2A079834
Starboard; 2A031052
My question -- Is there a way to inspect the inside of the manifold or riser for blockages without removing it? I think there may be some plugs built into it. I'm handy, but I'm not a mechanic so trying not to do any harm.
Background engines are raw water cooled in salt water with CATS and the Dry Joint original 2013 exhaust. I've been getting guardian faults off and on on both engines since buying in 2020 but it's getting more consistent. Starboard engine had the latest with it triggering guardian mode. I was at a loss until I bought a Rinda Techmate pro and finally plugged it in. It's now clear to me that the Port side Exhaust Manifold Coolant Temp (EMCT) Sensor seems to be the issue. Fault history showed 220 degrees which is too high. Like most people who have researched the Merc Dry Joint exhausts, I'm hearing very little in the way of a maintenance schedule for replacement. One person on this forum @Searay205 advised that he removed manifold and they were spotless inside. I think it's unlikely that my exhaust could be 9 years old and still good. However, my mechanic (who is all but retired but coaches me for free on the phone) says he has never seen them fail on the inside before failing on the outside. He suggested that I swap the EMCT sensors to see if they give the same readings from the opposite side. I did that on my Starboard engine and the Port side EMCT is still running 50 degrees higher at low rpms on the dock. I didn't test to see if I could trigger the alarm yet... Also when I swapped it, the port side was dry (unexpected), but the starboard side drained some water (expected). To me this means that the flow of water is getting plugged up in the Port side 4" elbow. I'm pretty much ready to bite the bullet on the expense to replace the exhausts (as much as $18K!!), but finding people who work on Sterndrives seems to be VERY difficult right now.
PS - Looks like I made a rookie mistake and hijacked an old thread vs posting new. Trying to figure out how to delete my post on the old thread...

 

[alldodge]

Hey, thanks for the info and serial number
Looked your starboard motor up at Mercury site and it shows closed cooled and only the elbow gets raw water. Your Manifold should use coolant from the heat exchanger. Elbow may need replacement one day but do agree with your retired Mech. it should show it self on the outside with something

Your motor may be running hotter for a few things. Raw water pump/impeller may need replaced. Heat exchanger may need to be cleaned. Thermostat or hoses may have an issue.

Do both motors temp show about the same?

 

[tpenfield]

Do the engines have Full closed cooling ? or a Half system

A picture of the engines would help in that regard. If I were in the situation, I'd be taking the exhaust system apart to see if there is a clog in the passageways which is restricting flow.

Salt water running through the new style (CAT) manifolds gets expensive, since they last about 7 years, and the replacement is crazy money.

 

[Ploring]

Hey, thanks for the info and serial number
Looked your starboard motor up at Mercury site and it shows closed cooled and only the elbow gets raw water. Your Manifold should use coolant from the heat exchanger. Elbow may need replacement one day but do agree with your retired Mech. it should show it self on the outside with something

Your motor may be running hotter for a few things. Raw water pump/impeller may need replaced. Heat exchanger may need to be cleaned. Thermostat or hoses may have an issue.

Do both motors temp show about the same?

 

[alldodge]

Holley Crud Bat Man, they are raw water cooled. CATs with raw SALT water, fresh would be bad enough, but salt, oh this is going to get expensive.

I feel really bad for ya

 

[Lou C]

Oh my God, that pic sums up why I'd never ever own one of these!
Either old school carbed I/O with wide open engine compartment for accessability
or
Modern 4 stroke outboard
or
A good condition Shamrock keel drive straight inboard with GM power, carbed of course...
that's all.

 

[Ploring]

Pic of starboard engine- my son helping to load the genset battery. I don’t think it ever had a heat exchanger. I am 99% sure I would be able to recognize but…. I have been wrong in life hahaha. Last year the water pump bearing started to fail on this stbd engine, so I bought a complete replacement online and my mechanic installed while in water. I do wonder about the thermostat hoses being plugged. If I attempt to disassemble the riser - what parts should I plan to have on hand?

 

[tpenfield]

O-M-G . . .


What those guys said. Raw water cooled. Why was I thinking closed cooling?

The outsides to look fine . . . so it is a matter of getting a look at the insides.

 

[Ploring]

Holley Crud Bat Man, they are raw water cooled. CATs with raw SALT water, fresh would be bad enough, but salt, oh this is going to get expensive.

I feel really bad for ya

Yeah I kinda figured replace exhaust when I bought her but …the CATS x 4 was a big miss!

 

[Ploring]

Oh my God, that pic sums up why I'd never ever own one of these!
Either old school carbed I/O with wide open engine compartment for accessability
or
Modern 4 stroke outboard
or
A good condition Shamrock keel drive straight inboard with GM power, carbed of course...
that's all.

It may be cheaper to repower with a quicksilver carb’d 383 honestly

 

[alldodge]

THIS IS NOT legal advice

Being a 2013 you might be in the time frame area of not mandatory. Its my pea-brain understanding that mandatory CATs were required in 2014. If this is the case "you might" (note the might and legal thing) be able to change to non-CAT

Yeah I kinda figured replace exhaust when I bought her but …the CATS x 4 was a big miss!

And if you do go back with CATs, I would strongly think about heat exchanges also. Its never been a good idea to go from a slat motor to antifreeze, but in this case I would think about doing it

It may be cheaper to repower with a quicksilver carb’d 383 honestly

Only if its legal, need to check

 

[Ploring]

Sorry forgot to answer this Q - both motors core temperatures are fine- it’s just the port EMCT fault’s on the port side Manifold’s getting hot. This was the starboard that day recently

 

[alldodge]

If it was mine, I would take the exhaust apart

 

[tpenfield]

I've seen invoices for replacing the CAT Exhaust on twin engines in the $12K range.

If you did an engine swap I'd go with the 6.2 350 HP SeaCore. (what I have). Probably cost a small fortune though.

Has the boat/engines been in salt water since new? They are not SeaCore either, by the looks of them.

go for something that looks like these . . .


.

.

 

[Ploring]

I've seen invoices for replacing the CAT Exhaust on twin engines in the $12K range.

If you did an engine swap I'd go with the 6.2 350 HP SeaCore. (what I have). Probably cost a small fortune though.

Has the boat/engines been in salt water since new? They are not SeaCore either, by the looks of them.

go for something that looks like these . . .

View attachment 365433
.
View attachment 365432
.

Those look really nice!

 

[Ploring]

Those look really nice!

Yes unfortunately it’s been salt since day 1. We bought her in August of ‘20. So you can imagine how nice it was to have an escape. I had a raw water cooled 7.4 on my last boat so got used to replacing manifold and risers on schedule but the Dry Joints have been a bit of a mystery on maintenance. I did have two of those blue plugs break off on the fuel cooler for “no reason” but maybe this is related??? I ended replacing them with stainless and anti-seize after a very salty water ugly engine room clean up (thank you salt away!!!) Thanks to all for your comments. I should have a full quote from a yard tomorrow. I am sure it’s going to be ridiculous.

 

[Ploring]

If it was mine, I would take the exhaust apart

I’m guessing it’s not as hard as I am probably making it out to be. I worry I will not have the right tools, snap a bolt head off, not have a good angle to get in to extract (shoot I don’t know if I have ever extracted). I’m you tube handy but I also break things.

 

[alldodge]

Breaking things can and do happen. Being a salt boat there is more a chance that can happen.

 

[Ploring]

Just an update here- I went ahead and ordered a pair of risers. I figured if only the port sides are getting hot then start there. Of course ordered a kit which came with 1 starboard and one port vs two port risers but I found that the post cat O2 sensor will reach even if it’s a starboard riser. I will swap if it works. Got them installed. Passages from manifold to riser and in riser were definitely obstructed! Test at the dock seems to show better cooling but real test on water pending.
Part2: Now I seem to have a new problem! My post cat O2 are faulting #354 and #355 On the Rinda. That’s an issue with the sensor heater not working. VesselView says I should “check the fuse”. My buddy tested the power to the sensor harness and it’s getting 13v so it’s not power but I don’t know? I CANNOT trace the sensor harness to a fuse however. Everything is bound up in tape and conduit. Anyone know where the O2 sensor fuses are??? On top of this I am getting a Starboard Cylinder Bank fuel trim too lean error #322. I feel like somehow I tripped the ECM into not being able to reach the sensors and now it’s definitely running rough. Misfire 10% of the time. Anyone know where the fuse is? Photos of the Rinda faults and some shots of the old port risers.

 

[Searay205]

You should have PMed me. I removed my cats years ago since the post O2 sensors kept failing after about a year (max volt cat simulator). You post cat O2 sensors are bad (obvious in picture), Wagner makes a replacement for the quicksilver/mercuriser O2 for about 60% of the price $55. When you removed the O2 sensors to replace elbows you torqued them, they rust and expanded again elbow and then when you unscrewed that busted the POS. Usually I recommend quicksilver but for an O2 sensor who cares. Pre Cat o2 sensors never seam to fail. With the new elbows your temp problem should go away. My manifolds were perfect same age as yours. In the elbows its the air to water interface that expedite corrosion.

The max volt cat simulator $460 works flawlessly and after 100? plus hours never a code for o2 sensor again. I love the smell of exhaust vs skunk also. My pinging with 87 octane also disappeared with removing the Cats generating 1200F heat. On my 100 plus mile trip Saturday my EMCT was 138F-140F is that cool enough??? I imagine my new elbows will be lifetime since my manifold temps are so much COOOOOOOOLER without the furnace fking cats. There you go, you want cooler EMT simple remove cats......

I looked at retrofitting old style manifolds but I glad I didn't, the new cat manifolds are very smooth, no square edges or corners for sentiment to build. Most old style manifold failures I seen is the result of sediment causing the manifold to overheat and crack. I sure you have the multi-drain system. A couple times a year when flushing open it up and let water go into bilge during flushing. This purges any sediment and makes sure all your check balls are clean in case you drain for winter.

Throw your old cats in attic if you remove. You can probably get $1K each for them. I believe they are $2400 new each, and that my friends is what killed the sterndrive engine and why we see outboards on everything until they require cats are those......

The POS cats are very fragile, you run rich you fk them, you shut engine off after hard runs without cooling the engine down (think run aground) you hurt them, all the alarms you have now, I think 41 vs 3 are to protect the fragile Cats. How much environmental damage was done making the cats? making o2 sensors that fail? for boats that see 500 hours in 10-15 years....

Your PCM is not a PCM 555 that is for not cat engine. I believe your is PCM 009 but I have to look at my manual which I don't have right now. You could always retrofit to a PCM 555 with new wiring harness and knock sensors but once you get past the cats your engines are reliable.