Mercruiser 377 MAG MPI overheating with Guardian (2014 260 EC)

drbeep

I'm at my wits end. I'm really hoping someone can help me.
I bought this boat a year ago and it has been one issue after the other. The biggest issue I have had is the over heating issue. It only overheats when approaching 4000 RPMs for 15 to 20 minutes. Guardian kicks in and I have to throttle back. Staying on idle does not cool down the engine. I have to take it 1500 RPMs to increase water flow and then it will cool back down. Temp reading is around 225' when guardian kicks in. Four mechanics have looked at this and each one did something different.


Here's what's been done so far:
New water pump and impeller
Heat exchange flushed
Lower unit intake inspected
Hoses inspected
O2 sensors replaced

Not related but also performed:
Fuel pump
Steering pump
Gas tank
Cap and Rotor

I have found two discussions online regarding this issue. 
One indicated to replace the Engine Water Pressure Sensor (881879T11). Ordered this.
The other is an issue described as Bravoitis. Definition from Offshoreonly: "The crushing of the forward end of the water hose and retainer of the belle housing to transom plate water hose, which will restrict water flow into the sea pump with a severe heat increase in the pump from friction and causing rubber impeller failure." I did have the lower unit removed during the gas tank replacement this was noted by the mechanic but I'm not confident he knew what he was doing.

Really hoping for some feedback from the community.

In addition to the over heating issue, Vessel View shot out an alert stating: Catalyst Oxygen Storage detected a fault. 


This didn't stop the motor from working and alerted hours before the over heating.

Thank you

YYZRC

Are the risers original?  Are you in fresh water or salt water?  Is the boat closed cooled?

drbeep

Good questions. Boat is in salt water. I bought the boat used so I don't know if the risers are original. One of the risers were running hotter that the other. It was removed cleaned. Temps are close to each other after the cleaning.
There is a raw water pump and a heat exchanger. I think this makes it seawater cooling.

LaRea

My vote is Bravoitis caused by corrosion in the fitting where cooling water passes through the transom.  Same thing happened with my boat, and it took months to figure it out.  You can inspect it with the boat in the water by disconnecting the hose fitting and checking for obstruction, but the repair is an out-of-water experience.

I'm assuming your boat does not have the "dual pickup" plumbing, with a second thru-hull water intake with a strainer.

Black_Diamond

There is an improved hose for the water intake on the Bravo’s. The original design can collapse under higher rpm if not installed correct. The new “Z” shaped hose has a hard plastic part now.  Almost certainly your issue. 

drbeep

Thank you LaRea and Black_Diamond.
To replace the intake hose, I see that the lower unit must be removed. Is this right?
Has anyone tried installing a through hull instead?
Thanks.

YYZRC

I wouldn’t bother trying to fix the bravoitis issue. Instead, add a thru hull pick up. Rinker did this on some of the closed cooled boats, including my former 2008 330. 

aero3113

How about your circulating pump (water pump) that’s mounted on the block? They can fail. The metal veins can corrode and cause loss of flow.

aero3113

actually if you have a heat exchanger your fresh water cooled.

drbeep

aero3113 said:

How about your circulating pump (water pump) that’s mounted on the block? They can fail. The metal veins can corrode and cause loss of flow.

I replaced a water pump already. Is there more than two?

aero3113

If you’re fresh water cooled the odds of the veins corroding are pretty slim. The circulating pump I’m talking about is the common water pump that’s on car instillations. It’s possible that there still could be an issue with it, they do fail on cars.

YYZRC

Usually when the circ pump fails it leaks at the bearing and stains the bilge below. 

drbeep

YYZRC said:

Usually when the circ pump fails it leaks at the bearing and stains the bilge below. 

No water leaks in the bilge is visible.

aero3113

Has anyone ever heard of a circulating pump vane slipping on the shaft? I wonder if it’s possible that can happen 🤷🏻‍♂️

Black_Diamond

Yes the lower unit needs to come off to replace that tube.  

Adding a thru hull to bypass the outdrive is not a good idea.  Al posted on that long ago. Part of the cooling for the outdrive is that water intake.  

Liberty44140

BD I believe Al said to not remove cooling through the bravo as the drive needs to cool, but he liked what my 06 342 350 horizons came with from the factory which was dual intakes. It got raw water both through the drive and a thru hull that came together in a y before a sea strainer that went to the pump. That should be the right system and probably what YYRC mentioned in his 33. 

YYZRC

^^ this - best setup. 

LaRea

I'm not a fan of dual pickups.  I bought that option on my 342, but I wouldn't do it again. 

When properly maintained, the Bravo 3 provides enough cooling water for up to 425 HP.  The dual pickup adds more points of failure that could sink a boat.  It adds more complexity and more things to service.  And I always had trouble getting my water pumps to prime after launching in the spring. 

YYZRC

I would be more concerned about being stranded at sea in guardian mode with a storm approaching than I would worry about the small additional risk of sinking due to an extra thru hull. 

LaRea

Admittedly, we're planning for low-probability events here.  Personally, I found the thru-hull system to be a pain in the stern when I had it.  

davidbrooks

Take a hard look at the water intake at the transom assembly. It is supposed to be replaced when you do bellows but is a real pain and a lot of mechanics skip it. When I replaced my transom assemblies the water hose was blocked. It had an opening the diameter of a Bic pen. 

kordo

May I suggest a simple test to help identify the problem.  Remove the blue drain plug on the water distribution housing on the starboard engine and run the engine at different rpms, note the flow.  Do the same for the port engine and if there is a difference, you have a problem before the pump.  If not, you have a problem after the pump.  This helped me identify a twisted water intake hose in the drive.  Good luck.

drbeep

kordo said:

May I suggest a simple test to help identify the problem.  Remove the blue drain plug on the water distribution housing on the starboard engine and run the engine at different rpms, note the flow.  Do the same for the port engine and if there is a difference, you have a problem before the pump.  If not, you have a problem after the pump.  This helped me identify a twisted water intake hose in the drive.  Good luck.

I have a single engine.

drbeep

The mechanic at the marina said that my engine is newer and the transom is a newer design that isn't prone to bravoitis. I took this pic last year when the gas tank was replaced and he confirmed. What do you guys think?



He suspects its the riser manifolds. This is a pic on the starboard side when the motor was removed last year.



What do you guys think?

LaRea

You personally took that picture last year?  You have what looks like a brand-new transom assembly.  Not gonna be Bravoitis.  

YYZRC

I would replace the risers. 

rasbury

So I have been here. A novice tree mechanic with no shade. 
Since you have closed cooling that takes a lot out of the picture. Our 270 closed coiling has the dual pick ups. I replaced the transom asy and with the motor out did replace the risers and the elbows- but the manifolds are coolant only so not a corrosion issue. 
Overheating a motor is serious stuff. Mine did and toasted the flappers in the exhaust which could allow water to flood the motor through exhaust. Inspect the plugs/cylinder for coolant? Engine oil? I figure overheating on a motor almost like a person having a fever- you have to figure it out! Thermostat? Could be simple...pull hoses or feel if water is moving? Two pumps, one for coolant and one for raw water to cool through the heat exchanger.  I'm not sure on my dual if the bravotitus got it that it would not pick up enough water through the thru hull to keep it cool...