2016 Mercruiser 6.2L ECT DTS Axius Cooling System Issue

If you haven't seen it yet, i found your service manual and it shows the water flow and suggests the strainer (F) I mentioned earlier is for the fuel module... The link will start at the beginning that covers both standard and closed cooling but you got to scroll through them to see the differences and the notes on the next page that may and may not cover the previous water flow guide shown of each design differences.


a -
Seawater inlet
b -
Seawater pump
c -
Power steering fluid cooler
d -
Y‑fitting
e -
Drain fitting
f -
Fuel supply module water inlet strainer
g -
Fuel supply module
h -
Distribution housing
i -
Drain fitting
j -
Y‑fitting
k -
Water circulating pump
l -
To engine block (from water circulating pump)
NOTE: When the poppet valve opens water will flow into (r and s)
90-8M0099748 eng DECEMBER 2015
m -
To crossover (from engine block)
n -
Crossover with 60° C (140° F) thermostat
o -
Exhaust manifold seawater inlet and drain
p -
Exhaust and seawater outlet
q -
Poppet valve assembly (green)
r -
Exhaust elbow seawater inlet (poppet valve closed)
s -
Exhaust manifold seawater inlet (poppet valve open)
t -
Starboard exhaust manifold drain hose
u -
Port exhaust manifold drain hose
v -
Starboard engine block drain hose
w -
Port engine block drain hose
x -
Oil cooler

I am up early this AM. I think this is the page you are referring to . . .
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Yes, thought you had the manual too but always worth a second scan through. Since you're up that is. good night on my end.

This diagram from the parts list shows slightly different routing to the poppet valve (I believe).
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More so need to go by the manual vs a parts guide as parts catalog is usually found off in its routings and then since your manual was made in 2017 vs the linked 2015, it would be worth seeing if they are the same or not and if different then the later one (17) is the up to date one mostly because mistakes were found as time went on either by MerCruiser employees or dealer service techs in the field and reported as so for correction...<That happens a lot more than one would hope.

Well, I’m also thinking the manual is the more correct version, as the only way for raw water to exit the system is via the risers. The manual more clearly shows that.

Ted, Im not an expert, just trying to wrap my head around some of the goofy crap from Fond du Lac

do you have the schematic of the glycol side plumbing?

i can see the manifold exit to the expansion tank in the pics. I assume the lower hose in just under the center cylinders is the supply for the manifold. and the riser has two supply hoses?.

the EMCT or Exhaust Manifold Cooling Temp would indicate the manifold and not the riser. or does Mercruiser call the riser temp sensor EMCT?




from the diagram, you have 4 O2 sensors and I am guessing that item 17 is the ECT sensor. which is not measuring manifold temp, however more riser temp

if so, the sensor is in the salt water. could you simply have a sensor that has corroded to out of spec?

may be worth swapping sensors to see if the issue follows the sensor.

also, you could have corrosion build-up on the glycol side. would be worth pushing a cheap $8 endoscope camera into the glycol side to see if you can see any corrosion buildup (without making too big a mess in your bilge)

@Scott Danforth and others . . . Here are the flow diagrams for both the raw water and the glycol sides of the cooling system.
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Raw Water Side

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Raw Water Reference Chart

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Glycol Side

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I'm headed out to the boat soon to finish up my work from the past couple of days. Hopefully will come back with some more Diacom Data.

Ted, I would almost measure flow in lines G. which in a closed system with hot glycol is a PITA.

Scott Danforth said:

Ted, I would almost measure flow in lines G. which in a closed system with hot glycol is a PITA.

Click to expand...

I could temperature probe it fairly easily . . . not sure about measuring the flow.

In other news . . .
I drained, neutralized, and purged the oxalic acid that had been sitting in the risers overnight. Then I buttoned everything up and took the boat out for a test run with Diacom recordings.

Starboard Engine (Fred)

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Port Engine (Barney)

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The good news is that with RPM's over 4K, I did not get an exhaust overheat warning, and the exhaust showed signs of cooling down once the rpm was reduced. Amazingly, I was getting about 20 psi raw water pressure at 4,000 RPM. So, progress has been made.

I plan on opening up the 'strainers' that are right after the oil cooler, to see what kind of danger lurks within. I doubt they have ever been 'serviced'. Essentially all of the raw water that comes into the engine must exit via the risers, so a flow obstruction leading to the heat exchanger can manifest itself as hotter exhaust temperature.

Ted, the rule of thumb with motors. 1/3 the fuel goes to turning the crank, 1/3 goes to heating the block, 1/3 goes to heating the exhaust

Scott Danforth said:

Ted, Im not an expert, just trying to wrap my head around some of the goofy crap from Fond du Lac

do you have the schematic of the glycol side plumbing?

i can see the manifold exit to the expansion tank in the pics. I assume the lower hose in just under the center cylinders is the supply for the manifold. and the riser has two supply hoses?.

the EMCT or Exhaust Manifold Cooling Temp would indicate the manifold and not the riser. or does Mercruiser call the riser temp sensor EMCT?

View attachment 410188


from the diagram, you have 4 O2 sensors and I am guessing that item 17 is the ECT sensor. which is not measuring manifold temp, however more riser temp

if so, the sensor is in the salt water. could you simply have a sensor that has corroded to out of spec?

may be worth swapping sensors to see if the issue follows the sensor.

also, you could have corrosion build-up on the glycol side. would be worth pushing a cheap $8 endoscope camera into the glycol side to see if you can see any corrosion buildup (without making too big a mess in your bilge)

Click to expand...

Hi Scott . . .

I hope this helps.
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The ECT (glycol temp) is in the crossover casting that is in front of the engine. "Item #17" is the EMCT, but in a closed cooling configuration it is more appropriately called the "RCT" (Riser Temp).

There is an internal block-off gasket (#13) that separates the glycol side from the raw water side where the exhaust manifold and riser mate.

The riser is feed by 2 hoses (orange arrows) leading from the poppet valve. Raw water pressure pushes the poppet open and gives flow to the lower hose (not sure what the psi threshold is to begin opening the poppet).

In a fully raw water cooled configuration (Red label 6.2L), the EMCT would be measuring the raw water as it flows from the manifold to the riser.

BTW - My O2 sensors say the exhaust gases temp is in the 1,435˚F range.

tpenfield said:

Hi Scott . . .
"Item #17" is the EMCT, but in a closed cooling configuration it is more appropriately called the "RCT" (Riser Temp).


BTW - My O2 sensors say the exhaust gases temp is in the 1,435˚F range.

Click to expand...

the labeling is what i figured.

thanks for that.

and at 1100+ is why when the raw water stops flowing, the rubber exhaust couplings that have a 250 F max turn into crispy critters...... its also why I run silicone/nomex hose vs the rubber.

tpenfield said:

is that with RPM's over 4K, I did not get an exhaust overheat warning, and the exhaust showed signs of cooling down once the rpm was reduced. Amazingly, I was getting about 20 psi raw water pressure at 4,000 RPM. So, progress has been made.

Click to expand...

good news on getting what ever flow obstruction in the system cleared out with the oxalic acid.

There is not much information about the 'strainer' (8M0095457) in the cooling system. So, as part of my checking of the cooling system, I took the cover off the strainer.
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Of course, it is smack dab behind the engine mount . . .

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Pretty much a bypass device with a 'screen' for the line to the fuel canister (fuel cooling).

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The body of it is open space for the larger amount of water heading to the heat exchanger. No other screen or anything on either end.

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So, I buttoned things back up and took the boat out for another run and ran some additional data recordings.

I'll post some graphs once I go through the data.

Here are my recordings from this morning . . .

Since I did the Port engine first yesterday, I started with the Starboard engine today. The key difference is that coming out of the harbor, the exhaust riser temp is in the 140˚F range and goes up from there. When I record the other engine, it is already up to cruising temperature (180˚F ish). The graphs show similar results as yesterday, just the situation swapped. I also did not run the recordings for as long as yesterday.
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Starboard:

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Port

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Today I ran the boat a little faster . . . more in the 4300-4400 RPM range. It was all good. Raw Water pressure was in the 20-23 psi running at/above 4K RPM.

Extended family peeps start arriving tomorrow, so the boat should be all set.

Nice Job Ted and thanks again for taking us all along for the ride too.
And glad you got things "cooled down" just in time for the enjoyment time of it all with the expecting of family.

Ted, drink one or two for us......

Thanks everyone . . . I appreciate the guidance and moral support.

I am not sure what the temperature is supposed to be. I looked in the engine manual (section 7) but did not see any specification for riser temperature range. I think 190˚F ish still may be too hot, but maybe the CAT risers run hotter.