2016 Mercruiser 6.2L ECT DTS Axius Cooling System Issue

nola mike · Jul 17, 2025

What was the solution last time? Did you try swapping raw water intakes between engines altogether rather than tying them together?

Scott Danforth · Jul 17, 2025

Ted, I would run some barnacle buster down the line, then see if the water pressure comes back. could also have a plugged HX. just pop the end caps off and look in the tubes.

tpenfield · Jul 17, 2025

I do run barnacle buster each year through the raw water side and let it sit over night, then flush and winterize.

Last time this happened the problem seemed to fix itself . . . maybe the barnacle buster did the trick.

For now, I found the white hose that I used last time to tie the two systems together and we shall see how that does. I think the exhaust risers might need some attention.

tpenfield · Jul 17, 2025

Quick update . . .

The magic white hose did the trick (for now) . . . both engines now getting sufficient water psi.

My sea water strainer set-up really needs an easy way to back flush. The strainer does its job and filters out the marine life that gets sucked in, but the downside is that it sometimes gets restricted.

Scott Danforth · Jul 17, 2025

Ted, not sure if your seastrainer fittings are bronze or marelon. however i recall someons makes a 3-way valve for hose flushing that you can run the motor in one position on a hose, backflush the seastrainer in the other position and the center is hose inlet plugged. dont remember who makes it. I believe it was marelon material, so maybe forespar

tpenfield · Jul 17, 2025

Hi @Scott Danforth . . . What's a marelon?

They are not bronze . . . a plastic of some sort as are the strainer bodies.

I have great ambitions of this being my last year with I/O's, so just trying to make it through the season

Lou C · Jul 17, 2025

Isn’t Marelon plastic?
Yeah every year I think the same thing last year with the I/O and just keep fixing it! Have thought of a much newer outboard boat but given I’m turning 70 in the fall I don’t know I’d get the use out of it for it to be worth it with our short season….

tpenfield · Jul 17, 2025

Lou C said:
Isn’t Marelon plastic?
Yeah every year I think the same thing last year with the I/O and just keep fixing it! Have thought of a much newer outboard boat but given I’m turning 70 in the fall ….

Me 2.

Scott Danforth · Jul 17, 2025

Marelon is the ABYC certified plastic used in thru hull fittings below the waterline

tpenfield · Jul 19, 2025

I’m getting exhaust over heat warnings on anything above 3600 RPM - so I assume that the risers will need attention.

tpenfield · Jul 19, 2025

This might be a question for @Fun Times , @muc , and a few others, but all are welcome. . .

This season I am seeing that the port engine is going into guardian mode (3000 RPM limit) when I run the engines above 3600 RPM. This has happened a couple of times, and generally the engines will run for about 10 minutes at 3700-3900, and then the port engine will go into guardian/3000. (Mercruiser 6.2 CAT engines - SeaCore ) The ECT values are in their normal range (165-169˚F) while this is happening.

To address the exhaust over-heat warnings that I am getting, I plan on doing a few things. . .

1) I'll run a Diacom recording for each engine and compare the exhaust temp readings (EMCT) for each engine.

2) I probably will take a look at the poppet valves. My understanding is that the valves allow additional water to flow to/through the risers at higher engine speeds. Let me know if I got that right . . .

I'm wondering if the poppet valve might not be working properly . . .

3) Finally, I'll take a look at the risers to the extent that I can see from the hose fittings. Maybe I should run an oxallic acid solution through them to see if that helps.

I'm at the peak of the family and guest visits for the next few weeks, so not a lot of opportunity to tear the engine/exhaust apart.

T.I.A. for any insight on the poppet valves or the exhaust over-temp.

Fun Times · Jul 20, 2025

dubs283 said:
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

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

View attachment 383689

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

Looking over your parts catalog I located an engine oil cooler like Dubs mentioned in 2023 which is item number 37 below, (and may had gotten confused with the power steering cooler which is usually open flow on the inside), https://www.mercruiserparts.com/bam/subassemblydetail/49503533/28372678

8M0107033 Mercury Marine Cooler OEM | eBay

New Mercury Marine Cooler OEM.

www.ebay.com

But just as or maybe a bit more importantly is it appears your model has a strainer in the cooling system already? as you added one too? that may need inspected...
See item numbers 16 / 17 in the parts link above which the strainer looks like this,

8M0095457 Mercruiser Stern Drive Bravo GM 6.2L V6 Strainer Assembly & Hoses | eBay

MPN: 8M0095457. This strainer is in goof used condition.

www.ebay.com

But yes, the exhaust check valves do basically wear out /get stuck too causing odd temp type symptoms so they should almost become a maintenance item because of your boats past life before you bought it plus the waters you tend to run in as well 'especially with the past experiences you had and mentioned in this thread.

As you can see in the parts catalog your cooling system has a lot of fittings that could get a bit clogged up too that might cause you issues but low on the priority list....Hopefully...

Just for the newer model 8.2lL oil cooler reference 8M0045696 looks like this, https://www.ebay.com/itm/285301281387?_skw=8M0045696&itmmeta=01K0KBJZ0Q2721SZ7CJQPWM3GE&hash=item426d48126b:g:RxYAAOSwHxJkb5lU&itmprp=enc:AQAKAAAA0FkggFvd1GGDu0w3yXCmi1cWOMFH6+GgPcGQGM2MoxzMJjYJGz0jAdQ2FIf1rZw6eG0LvpxXOIME8hcmWrIdWx1auyfiXCc0Yf07r6/WCt5TfwMU1cQs4H9hFVybc+LMvXoEUnB5sqLaaWWoRPUtabGdGitaXl3vaqK7lhLBEECz0WhAxh0CpaaIYH9Iw9mAKwbqvJqXjzch8ViwrlAPo5M4MyDv8b+OdjGa/dADHkUSNAMTvIvt1QpAN/m4Jb2/nwn8eg+3ri1vqIoVyTlia/E=|tkp:Bk9SR77wy-uEZg

Genuine Mercury Marine parts, large inventory, fast shipping. 6.2L MPI 350 EC 2A456613 THRU 2A530775

6.2L MPI 350 EC 2A456613 THRU 2A530775

www.mercruiserparts.com

And don't forget your Poppet Valve Assemblies

Check valve Items 19 - 23 and then the high up in the box is a check valve number 29, https://www.mercruiserparts.com/bam/subassemblydetail/49503521/28372678

MerCruiser 6.2L 300HP 377CID Riser Check Valve & Barb Fitting PN 8M0103408 | eBay

Find many great new & used options and get the best deals for MerCruiser 6.2L 300HP 377CID Riser Check Valve & Barb Fitting PN 8M0103408 at the best online prices at eBay! Free shipping for many products!

www.ebay.com

tpenfield · Jul 20, 2025

Thank you for the reply . . . I will look into the 'strainer assembly', as that may have some residual blockages from the 5 years of operation prior to my putting sea water strainers in before the sea water pumps.

tpenfield · Jul 20, 2025

I think I found in this picture where the 'strainer' is located.
.

.
I'll take a look and see if that is clogged, etc. If not, then I'll take a look at the poppet valve.

Fun Times · Jul 20, 2025

Oh boy, that looks fun to get to and add a bonus to that photo, you found the oil cooler too.

tpenfield · Jul 20, 2025

Fun Times said:
Oh boy, that looks fun to get to and add a bonus to that photo, you found the oil cooler too.

Are you pulling an all-nighter?

My California peeps will be here next week, so hoping to have the boat operational for their visit.

And yes, the port side of the port engine is nearly impossible to get to. I might practice on the port side of the starboard engine first, as that is an easier reach.

Fun Times · Jul 20, 2025

tpenfield said:
Are you pulling an all-nighter?

My California peeps will be here next week, so hoping to have the boat operational for their visit.

And yes, the port side of the port engine is nearly impossible to get to. I might practice on the port side of the starboard engine first, as that is an easier reach.

Today was a workday with tomorrow off but have plans in the early afternoon to go look at a car as a gift for someone in the family today but lately we've been staying up late like this on Saturday's thinking we're missing out on something in life if we went to bed so early with the day off on Sundays.

But getting ready to go get some rest in a few but definitely I wanted to do some studying on your engine issues to see if maybe I could help get you headed in some sort of direction before turning in.

Hope you can get something figured out in time to enjoy the time with the CA friends.

It would be nice to see what's physically inside under that cover of the strainer as I didn't even know it was there until I saw it in the parts catalog tonight... Perfect to do a small write up on it as you're good at doing write ups as you endure these engine adventures.

tpenfield · Jul 20, 2025

I've grabbed a few images from the Internet that show the parts under discussion.
.

.
Above is the rear view of the engine, showing the P/S cooler and poppet valve. It looks like water to the risers branches off at the back of the engine via the 'Y' pipe (#12 - 8M2003728). So, the 'strainer' would not be part of the raw water flow to the risers. I think my focus should be on the poppet valve at this point, and then the strainer as needed. (for now)
.

.
I believe I have the primary and secondary hoses from the poppet to the risers labeled correctly ? .

My guess at this point would be that I am not getting good flow (if any via the secondary) to the risers.

tpenfield · Jul 20, 2025

Also, I've been wondering what these things attached to the fittings were . . .

.
Apparently a check valve (8M0103408) . . . I guess it is to allow the raw water hose(s) to drain while the engine is not running?

tpenfield · Jul 20, 2025

Update for today . . .

I checked the following . . .

Port engine:

Coolant in H.E. = full (both engines were & are full)

Poppet valve: I removed the cover of the valve assembly . . . no build-up or anything and the spring action of the valve seemed normal . . . I could open the valve with a moderate press (maybe a few pounds of force)

.
Secondary Raw Water Hoses to Riser: I removed both port & starboard hoses (of the port engine). Slight rust and scaling, but nothing major. I probed the fitting and could easily get into the water duct within the riser. I then left each hose disconnected and briefly started the engine so that raw water would flow out the secondary fitting, which it did.
.

.
Since there was nothing obvious, I took the boat out and ran some Diacom recording for both engines . . .
.
Port Engine:
.

Port-Engine-EMCT-July-20-2025 - Copy.png

.
Starboard Engine
.

Stbd-Engine-EMCT-July-20-2025 - Copy.png

.
It looks like the starboard engine is able to recover, while the port engine riser temp keep going up.

I'm not sure at what temperature the Guardian kicks in, but I would think it is 200+˚F

Tomorrow, I will take a closer look at the risers.

2016 Mercruiser 6.2L ECT DTS Axius Cooling System Issue

Vice Admiral

Grumpy Vintage Moderator still playing with boats

Moderator

Moderator

Grumpy Vintage Moderator still playing with boats

Moderator

Supreme Mariner

Moderator

Grumpy Vintage Moderator still playing with boats

Moderator

Moderator

Moderator

Moderator

Moderator

Moderator

Moderator

Moderator

Moderator

Moderator

Moderator