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

[Searay205]

The first thing I would do is become intimate with your cooling system and how it flows. how enters and where it goes. You can do that in Air Conditioning there are diagrams everywhere. Second since you have a huge boat is validate flow while in the water so you dont have take it out. I shooting from the hip and thats easy for forum members to do as I not physically working on your boat.

 

[Ploring]

Update: Hi All - Based on all of the feedback on this forum, the fact that the exhaust seems (by all record) to be 9 years old WITH raw water cooling, I opted to continue with the exhaust "flow restriction" testing instead of Bravo-itis testing. If you recall - I had done both Port Risers previously. Temp at higher RPM's improved but I still ended up with EMCT faults/guardian mode. So... Today I replaced the manifolds the port sides of both engines. Took her out for a spin. Port side was flowing beatifully!! Never and PORT EMCT never got above 125 degrees!! HOWEVER the STARBOARD side ended up getting hot and faulting out at 212 degress.... SO, to me, it's pretty clear that I have a restriction problem and both sides need to be updated. I'm probably wrong about something but this seems like the most logical next step. Manifolds and risers for both engines on the Starboard side are now on order... $3500 with shipping. So I'm up to $7K, but I'm not replacing the CATs or the rest of the accouterments (sensors, plugs, ball valve etc.). I will let y'all know the outcome once it's installed.

 

[alldodge]

Geezers that's expensive

 

[Ploring]

Here are repeats on the TIPS that I picked up here for REMOVING the 78 pound manifolds.
- Grab a 2x4 and cut it to fit across the engine compartment over the manifolds.
- Use a strap that has a "cinching clamp" on it to support the manifold off the 2/4 with the strap while taking out the bolts.
For INSTALLING
- Grab some 3/8's "all thread" bolt material (coarse thread 16). Electricians use this for hanging conduit. Create 2 headless studs that are 5 1/2" long. The manifold bolts are 4 3/4 so being longer the studs allowed for extra that a made it easy to back them out later.
- Screw the studs in on either end of the block and dry fit the gasket then slid the manifold onto them. Allowed us to "hang the manifold: while we fitted the rest of the other manifold bolts in. Then we backed these studs off and put the final two bolts in.
- Also I was really worried about one of the manifold bolts being frozen into the block. This was NOT a problem. The Bolts came out super easy.

 

[Ploring]

Yeah - I imagine these cost 2x as much as they would have in 2019. Covid-flation. Bummer. I had planned to do the exhaust given the age of the boat but I figured about half the price.

 

[Searay205]

Well before you throw the old manifolds away do some destructive testing with a sledge hammer and safety glasses. Real cool if you had a port band or band saw you could slice in half.

 

[Searay205]

PartsVu have the manifolds for $629 with free shipping. I think they charge tax. Elbows vary depending on height.

 

[Ploring]

Update- starboard side completed last Sunday. It appears to be a success!
Sea trial results:
Port sides Avg. EMCT : ~110 degrees
Starboard sides Avg. EMCT: ~125 degrees
RPMs: 3950 both engines
Speed over ground: 27 mph
Test at speed: 8-10 minutes.
Short test but this was plenty long based on prior faults.
Pictures of riser bottom port was totally plugged, gasket was starting to compromise. Other pic is inside of the riser exhaust exit buildup. I was dangerously close to doing damage to my engine.
Thanks to everyone who responded. You helped figure it out and gave me confidence to try to repair it myself. … fingers crossed that this will hold up!

 

[tpenfield]

Nice work on replacing the exhaust. A raw water cooled engine in salt water is going to have a limited life span. Getting 9 years out of the exhaust is a good run. At some point, the engine block want some attention. 15-20 years on the block in salt water is a good run as well.

On your next boat, you will want to look for a full closed cooling system (or outboards) Most of the 350 and 6.2. SeaCore engines are set up with full closed cooling. The 8.1's are not - block only.

 

[Lou C]

Here in the salt I’ve replaced the exhaust every 5-7 seasons & have avoided problems with overheating & clogging. On my old OMC one piece exhaust the ports were pretty small & started to clog between years 5-6. The later style center riser exhaust I replaced them with has much larger ports so they may last a few years longer. This engine has been in salt 20 years and I’ve replaced the exhaust 3 times over that time interval. Each exhaust system cost wise was about $750 for parts.

The raw water cooled engine, well my experience is that the blocks don’t rust thru but the hottest parts of the cyl heads can after many seasons in salt water.
I replaced the heads after a head gasket failure because the machine shop that checked them out found cracks (past overheat) and the cooling passages were getting eroded due to salt water use. So changing the heads after about 15 seasons can give the old short block a new lease on life. Any new or reman engine I’d put in would for sure have closed cooling! Two must haves for an inboard are closed cooling & a remote oil filter…I’m getting tired of pulling out the seats to get at the drain plugs & the oil filter every year for winterizing…

 

[Searay205]

This validates my theory, only the exhaust elbows get consumed. Manifolds stay good. All that rust and crap that looks horrible in you pics is in the gas water stream at exit, no way water can go from exhaust to combustion side that far down stream. When I replaced mine just based on time (no temp issues) I actually twisted the exhaust elbow in half trying to get out of rubber bellow then had to smash the bust half out of rubber bellows. Again no overheat and obviously no water in engine.

Great news is it wasn't the bravotis,

 

[Lou C]

here's what my old OMC batwings looked like after 5.5 seasons in our salt water. Not to bad, one port is clogged.
next pic is the later style 2 piece exhaust, see how much larger the cooling ports are....but they run at exactly the same temps....at idle about 100, hottest they get is about 135* after coming off plane.

 

[Searay205]

I suspect if you ever remove your cats you will see much less fouling and plugging in the future. Instead of 900f plug going through your elbows on the gas side, trying to boil the salt out of the water you will just have 180F gas temp since the gas is cooled as it goes through the manifold. Your outdrive would appreciate it also.....

 

[Ploring]

Had another long trip on the water this weekend 26nm in total. Many of the miles at 4000 rpms. I agree in full - next boat or next set of engines needs to be closed cooling or OB's. I also know that I need to check the risers/elbows a lot sooner than the last time. Now that I know how I'm in a better position to be proactive about it.

 

[Searay205]

2013 to 2022 or 9 years of continuous salt water exposure (I assume you keep in the water around the clock) is impressive. Failure wasn't result of manifolds/elbows allowing seawater into engine, it was high temperatures. I think you run manifold(s) to high temperature alarm. Why not? This assume you play in the same lake, and you are not doing the "loop" or thousands of miles in one trip.

 

[tank1949]

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...

if you got 9 years out of any iron being exposed to salt water, you have been lucky. I'd pull all that have been soaked in Salt water and manually test. 18K for risers and manifolds seem very high, but I am cheap and do most of mechanic work myself.

 

[Searay205]

its not 18K for risers and manifolds. Its 18K for 4 catalytic converters (should be reused) 8 oxygen sensors (should be reused) and gaskets. Manfolds and elbows for 5.7 mpi is $2500 delivered. I don't know where the 18K came from but I am sure someone will take it if you pay it.

 

[Ploring]

if you got 9 years out of any iron being exposed to salt water, you have been lucky. I'd pull all that have been soaked in Salt water and manually test. 18K for risers and manifolds seem very high, but I am cheap and do most of mechanic work myself.

Honestly if I had the time and the inclination I probably could have taken @Searay205 's suggestion and used a pressure washer to try to blast everything out of the water ports in the manifolds and risers to see if that could clear them enough. It did not appear that the manifolds were rotted so much as the ports were just REALLY clogged up. The question I guess is what was it that was clogging them? Was it built up scale or was it bits of iron (from the engine core) wrapped in scale. I reused almost all of my temp and O2 sensors (one 02 sensor was replaced) and brass plumbing fittings. All in with MA taxes and shipping it cost $7K for all the parts (4 manifolds, 4 risers and respective gaskets). I did NOT shop hard for price, I was looking for availability. I did reuse the CATS and all the original bolts. They didn't look great but they tested fine. For the cost of a $45 riser gasket, I'm TOTALLY cool waiting for the CATS to fail. CATS are about $2900 EACH to replace. One local shop said they would do a 100% replacement of the exhaust system (including all 4 CATS) for $24K PLUS labor which they estimated to be a WEEK ($7K). Took me and my buddy about 8 hours to do the whole thing (and we slow because we were learning). One could say I saved about $24K but I'm sure the shop would have used more new parts so it's not apples to apples.

 

[alldodge]

The shop that replaces CATs can take them to the junk yard and get a few hundred for them

 

[Searay205]

Please don't ever replace your cat elements, eliminate them. Get rid of 4 rear oxygen sensors, run cooler exhaust, mitigate the chance of pre-ignition, extend life of exhaust elbows. Take savings and donate to local parks and wildlife. I am surprised you get more than 18 months out of your rear O2 sensors as they stay wet weeks after boat removed from water. Check out pic below. I smashed my elbow open with a sledge hammer so you can see how much wall thickness remained. 12 years of saltwater use (FLA and TX). Zero overheating issues. Zero saltaway. On a side note I bench press 190lbs 8 times and I really had to smack it numerous times to break it open so tons of collateral damage just due to smashing. On the secon pic you can see how part of the elbow broke off when removing from rubber boot. who cares that where exhaust and water meet. on new one and old one you can see how small the discharge water passages are, on bottom a 3/16"? hole and top is a rectangular discharge.