2016 Mercruiser 6.2L ECT DTS Axius Cooling System Issue

[tpenfield]

Greetings,

Branching off from my 'boat is being a boat' thread, I am posting about an issue with the starboard engine cooling system (Serial # in my signature below) Keep in mind that the engines in my boat are the in-house Mercury built engines, not the GM 6.2 that preceded them.

Fun Facts

• New impeller last year (about 30 hours on the impellers, they are spec'd for about 300 hours between replacement).
• Sea water strainers on both engines BEFORE the seawater pump.
• Bravo 3 outdrives with both side and nose cone water pickups
• SeaCore version of the 6.2, so full closed cooling.

Symptoms and efforts so far:

1. Raw water pressure is low on starboard engine at cruising speeds (spec is at least 20 psi at 4000 RPM)
2. At low RPM both engines are within spec for raw water psi, and in fact the starboard engine reads higher than the port engine.
3. As the RPM increases the port engine psi rises as it should; the starboard engine reaches 14-16 psi and goes no higher. See the screen shots of the raw water psi
4. I cleaned out the sea water strainer on the starboard engine as it had some marine life debris in it. No difference.
5. I sealed off the fitting for the fresh water flush, in case the valve was leaking air. No difference.
6. I ran the boat at WOT for about 1 minute to see how the raw water psi and ECT reacted. the psi was port 24 psi, stbd 18 psi both at 5200 RPM. (Boat speed was 42 mph) port ECT was 171, stbd ECT was 178.
7. I ran the engines up to about 4900 RPM for another 30 seconds or so, noting that the WOT run had gotten the stbd psi up a bit. (from about 14 to 18). After the short run @ 4900 RPM, the starboard engine went into guardian mode, based on exhaust temperature. (see vessel view warning message) 2000 RPM limit . . . I limped back to the mooring to go fetch my Diacom computer.
8. No codes as per the Diacom. I ran about 4 minutes of recording at about 3600 RPM and noticed that the starboard side exhaust manifold temperature (Stbd EMCT) was about 25˚F higher than the port side of the engine (Starboard engine for these) (see video)

VesselView screen shots . . .
Stbd engine starts out higher in psi than the port engine

.

.

.
Stbd engine 'hits the wall' at about 2000 RPM and pressure does not rise thereafter.
.

.

.
After the high speed runs . . .
.

.


Diacom recording . . .
.
View attachment IMG_4921-a.mov
.
Looking for input, ideas, next steps.
.
I am thinking that there is a restriction somewhere before the sea water pump, which may explain why the psi starts out higher than the port engine, but then reaches a limit (14-18) psi. This has been the case on all of my 4-5 outings this year.

At cruising speeds (3500 ish RPM) there seems to be enough water flow to avoid any guardian issues. I'd like to see if I can resolve it, as it may only get worse, and probably cause more guardian mode when it is most inconvenient.

FWIW - on my previous boat, I did have a barnacle shell that lodged itself in the water intake at the bell housing. I'd hate to have it be the same thing.

I have a new impeller on order, just in case.

Here is a link to the Diacom recording file if any of the mechanics on the forum would like to take a look. https://drive.google.com/file/d/1DRqUjdCDcdxvhezkGRUdQvS_hv0NElaP/view?usp=drive_link

 

[tpenfield]

Quick update . . . my video stopped a bit short of the full recording. The stbd side EMCT got up to 186˚F while the port side was at 161˚F . . . so 25˚F difference. Not sure if that is significant enough or not. Perhaps so on a WOT run. I am also not sure what the EMCT is reading Coolant or raw water exiting to the risers.

 

[alldodge]

I'd like to know more about the exhaust sensor that told the PCM it's to hot

Next, have you tried swapping the water pressure sensors?

 

[drewm3i]

Temps verified at the exhaust with an IR gun? Has a past impeller blown up in the cooling system before? On my 454, I found a lot of pieces at the oil cooler when I first got the boat. You may vary, but I would check the PS/Oil cooler if you have one.

 

[tpenfield]

Thanks for the replies . . .

The water pressure sensor is buried amongst hoses, not an easy swap. I suspect that the pressure is probably reasonably correct, given the exhaust overheat.

The impellers that I removed last year were in very good shape. 100% intact. The water pressures last year were very consistent.

I did some IR gun checking with the engines at idle and did not see any significant differences, side-to-side or engine-to-engine.

I may do the Diacom recording at higher RPM to get more data, or even if it goes into guardian mode.

 

[Lou C]

Since the Guardian was active due to exhaust overtemp, I'm wondering if there could be some clogging in the exhaust elbows. Not sure how long the new style exhaust elbows last in salt water but the boat is '16 that means that it has done 7 seasons? Was it used each season? I haven't heard a lot about the new cat converter exhaust so I'm not sure if you have to follow the same protocol we follow in salt water: every 5-7 seasons, at least inspect the elbows and manifolds, and replace anything that looks questionable.
Would the water pressure read out drop if there was clogging in the elbow on that side?
There is always I guess the possibility of marine growth in the water intakes or internal water passages of the outdrive on that side, I had that problem about 10 years ago and wound up having to split the drive to remove the plastic water screen that was behind the water intake holes in the lower unit. Try as I might I could not get stuff to quit growing on it, so I tossed it and it's been running at normal temps ever since (160).

 

[Scott Danforth]

Ted, pull the PS cooler and check for debris.

 

[tpenfield]

Since the Guardian was active due to exhaust overtemp, I'm wondering if there could be some clogging in the exhaust elbows. Not sure how long the new style exhaust elbows last in salt water but the boat is '16 that means that it has done 7 seasons? Was it used each season? I haven't heard a lot about the new cat converter exhaust so I'm not sure if you have to follow the same protocol we follow in salt water: every 5-7 seasons, at least inspect the elbows and manifolds, and replace anything that looks questionable.
Would the water pressure read out drop if there was clogging in the elbow on that side?
There is always I guess the possibility of marine growth in the water intakes or internal water passages of the outdrive on that side, I had that problem about 10 years ago and wound up having to split the drive to remove the plastic water screen that was behind the water intake holes in the lower unit. Try as I might I could not get stuff to quit growing on it, so I tossed it and it's been running at normal temps ever since (160).

My thoughts are that if the restriction were at the end of the sea water flow (exhaust) the pressure would be high, if not higher than it should be. If the restriction were earlier in the coolant flow, then the sea water pump would be 'starving' for a full supply of water.

Another thing is that the restriction (where ever it is) does not really come into play until the flow rate increases. I have the water flow diagrams, so maybe I'll go over them to see if anything makes sense.

Head scratcher for sure.

 

[tpenfield]

Ted, pull the PS cooler and check for debris.

Yes, that makes sense. Particularly if a pice of the impeller broke off as the next stop is the PS cooler. Just have to find it at the back of the engine.

 

[tpenfield]

Quick Update . . .

There is a temperature sensor at the bottom of the exhaust riser - Mercury P/N 885342002. So, I assume that is what the 'EMCT' temperature readings are from. I answeredmy question, the EMCT is the raw water and the ECT is the coolant. I can run a recording of the port engine for comparison.

The current theory would be the low water pressure is not creating enough flow on the raw water side to properly cool the exhaust, so it goes into Guardian mode at a certain temperature.

If I do find debris at the P/S cooler, it would probably mean that the 30-hour old impeller lost some bits.

 

[tpenfield]

Just reading through some dialog and comments about EMCT overheat issues, I came across this one comment . . . "Too many things to go wrong with Smart Craft. Gets your blood pressure up and your wallet out. This will be my last boat with SC. Analog worked well for many years, KISS"

Funny

I am also wondering if the later year model Bravo outdrives still have the "Bravoitis" issue? The boat has lived in salt water seasonally June 2016 -> July 2023. First was Stanford CT (4 years), then Manor Harbor NY (2 years), now Falmouth MA (2 years).

My current theories are:

• Marine life restriction at the bell housing intake.
• Bravoitis
• Impeller bits at P/S cooler

One other thing to mention is that I ran 'de-scaling' solution in through the raw water side during pre-season prep. Let it sit overnight and flushed it in the morning. On my previous boat, I found this to be an effective way of purging the calcium build-upon the raw water side.

 

[dubs283]

Until you gets eyes on parts everything with your issue is speculation. It's good to get ideas but until put to practice they're just ideas

The suggestion of checking the p/s cooler is good. Do that. My guess is the cooler isn't honeycomb like older styles though, but still worth a look

Unsure if your engine has an engine oil cooler like the 8.2L engines. If so, they are honeycomb and do collect debris quite easily

I would bypass the sea strainer prior to the sea water pump. Seen more than one draw air without leaking much/any water during operation/static

If all this yields the same result ime it's time to start taking major components off/apart

 

[Scott Danforth]

You found a shell last time, this time you find Nemo?

 

[tpenfield]

You found a shell last time, this time you find Nemo?

We should take odds on the likely causes and see who wins . . .

 

[Scott Danforth]

I need to find a restriction myself....... Last trip out my pressure was low. However I have an outboard pressure gauge hooked to a tee fitting .... No smartcraft, just old school analog.

 

[tpenfield]

The P/S fluid cooler is P/N 8M0095482. I believe it looks like this . . .



I am wondering if it is a straight-thru cooler as Dubs mentioned, rather than the honey comb style.

 

[nola mike]

My thoughts are that if the restriction were at the end of the sea water flow (exhaust) the pressure would be high, if not higher than it should be. If the restriction were earlier in the coolant flow, then the sea water pump would be 'starving' for a full supply of water.

Another thing is that the restriction (where ever it is) does not really come into play until the flow rate increases. I have the water flow diagrams, so maybe I'll go over them to see if anything makes sense.

Head scratcher for sure.

Are you able to see which temp rises first? WAG is that once you start to stress it and pressure doesn't rise, exhaust temp would rise first followed by ECT.

 

[tpenfield]

Are you able to see which temp rises first? WAG is that once you start to stress it and pressure doesn't rise, exhaust temp would rise first followed by ECT.

Yes, I can play back any of the data from the recording to see how they relate.

The software only let's you choose 3 elements at a time for graphical display.

 

[Scott Danforth]

it should be a 50 tube bundle of 1/4" copper tubes.

 

[tpenfield]

We went locally today, so as not to risk it. Only 12 psi at 3400 - 3500 RPM. It was at about 15 psi coming out of the harbor, then dropped once getting up to cruising speed.
.

.

.
it certainly seem like something is floating around in the raw water side and gets sucked into a restriction at higher RPM.

I kept the speed at a moderate level to avoid Guardian mode.