2012 5.0 Ltr. MerCruiser overheating issue

[Chris Harrington]

Hey there, I have twin 5.0 Ltr. mercruisers on my 2013 Bayliner 315 cabin cruiser. I have been chasing an overheating issue since last summer in my port engine. Looking for some ideas as I've tried everything I've heard from experts to forums.

Here are my specs:

• Saltwater boat (short season, east coast of Canada)
• 400 hours
• Raw water cooled
• I have done some of the work but I have a very capable mechanic (who is very busy this time of year with our very short season in Nova Scotia).

Symptom:

• Takes the usual 10 minutes to get up to 175F
• Slowly makes it's way up to 200-225 then alarms
• sometimes revving in neural at 2500 rpms will lower the temp but then when at idle temp will rise again.
• Same symptom in the water or on the hard with muffs.
• Run the same tests with idle and rev with the starboard engine and it's fine, hardly goes over 175.
• Oil is clean, no sludge, milk or signs of water.
• Motor runs smooth.
• Very good flow of water coming from my exhaust. Not always hot though. You would think with an engine running 200k and about to alarm would be putting out hot water from the exhaust sometimes it does.....

What we've done so far and in this order:

1. Replaced the single point drain (threads broke off at the drain plug, not really relevant but this was about when the heating issue started last summer, adding for sake of details)
2. Replaced the thermostat.
3. Checked surface temperatures of hoses etc with lazer thermometer to be assured I am actually having high temps and not faulty sensors or guages. Engine is running hot.
4. Replaced the raw water pump (pump didn't look to bad but replaced it anyway.
5. Replaced riser and elbow gaskets (there was some restriction and thought that was my issue bit no luck)
6. Replaced central water pump (didn't look that suspect when took the old one out but replaced with new anyway.
7. Removed risers, elbows (again) and took manifolds off this time. Cleaned out bottom of manifolds as they we packed at the 2 bottom cleanouts with a carbon like black material then usual bits of rust I'll add a picture. Got water running much better through all ports with a water hose. Figured this was my fix. Not so .
8. Checked for Bravo-itis. While having the manifolds off we were able to remove and check the bell housing fitting and intake hose that goes to the raw water pump. All clear...
9. Tried running with no thermostat also. No difference.

What I haven't done yet.

1. I have not removed the drive on the port side (the overheating side). Just did some extensive work in the starboard side. Gimble bearing and some shifting work.

Ok, Go! Hopefully....

 

[tpenfield]

I had a similar issue that caused overheating for a season of boating. Did & checked everything . . .

At the end of the season, I removed the outdrive and there was the issue. a shell had grown inside the outdrive water duct, dislodged and was partially blocking the intake hose that goes from the bell housing to the transom assembly.

Removed the shell, checked the outdrive water duct for any more debris, problem solved.

 

[tpenfield]

BTW - you mentioned about getting cool water out of the exhaust ports. Keep in mind that a fair amount of the cooling water by-passes the engine and goes directly to the exhaust to keep it cool.

If you have restricted water flow, then there may not be enough pressure to 'push' enough of the hot water out of the engine.

Also, since you are raw water cooled and in the ocean, the insides of your engine block and cylinder heads probably look a lot like the exhaust manifold with the heavy scaling. It is possible that you are getting restricted flow withing the engine . . . probably the cylinder heads.

The remaining life expectancy of the engines is down to a few years at this point, this being its 12th season in the salt.

 

[Chris Harrington]

BTW - you mentioned about getting cool water out of the exhaust ports. Keep in mind that a fair amount of the cooling water by-passes the engine and goes directly to the exhaust to keep it cool.

If you have restricted water flow, then there may not be enough pressure to 'push' enough of the hot water out of the engine.

Also, since you are raw water cooled and in the ocean, the insides of your engine block and cylinder heads probably look a lot like the exhaust manifold with the heavy scaling. It is possible that you are getting restricted flow withing the engine . . . probably the cylinder heads.

The remaining life expectancy of the engines is down to a few years at this point, this being its 12th season in the salt.

This is helpful. Thank you. With the amount of water coming out the exhaust it seems like there would be plenty of water going in. But you're correct, doesn't seem that the hot water is getting pushed through the engine. Removing the drive is the next plan. Yes, up here in the cold salt water we seem to get about 20 years out of an engine. Keeping in mind we're only in the water about 4 or 5 months a year. I know taking it in and out of the water is likely worse than even leaving them in the water as it comes to salt in your engine.

 

[tpenfield]

The amount of time in the (salt) water does not seem to matter much. Once the engine is exposed to the salt, the oxidation process begins.

If/when you get to the point of re-powering consider a FULL closed cooling systems to get good longevity out of your engines.

 

[Chris Harrington]

Put water hose direct to the line before the raw water pump, eliminating the drive and it still overheated. Took about 15 minutes at 1500 rpm.

 

[Fun Times]

Need your engine serial number to help confirm yours has these items but you may want to try thoroughly inspecting the thermostat poppet valve and especially exhaust check valves at the bottom as they have been found to make the engine run hot if not working properly.

Item 11 and 15,

Thermostat and Housing, Standard Cooling​

Thermostat and Housing, Standard Cooling

www.mercruiserparts.com

Item number 19,

Exhaust Manifold and Elbow​

Exhaust Manifold and Elbow

www.mercruiserparts.com

350 MAG MPI ALPHA/BRAVO EC - 1A300000 THRU 1A611927 and MORE​

350 MAG MPI ALPHA/BRAVO EC - 1A300000 THRU 1A611927 and MORE

www.mercruiserparts.com

 

[Lou C]

I’d do the clear hose test to check for combustion gas getting into the cooling water from possibly leaky head gaskets. Temporarily replace the hoses feeding the manifolds from the thermostat housing with clear reinforced hose. Ideally test in the water & run it at idle & on plane while a helper watches for bubbles in the water flow. You can get more years from a raw water cooled engine in salt if you identify the cause & repair what’s needed. Might need new head gaskets & cyl heads inspected. I was able to do that with my old 4.3. Overheat damage from 2013 caused blown HGs in 2016. Fixed it that winter/spring of 16/17. But…I was getting bubbles in the clear hose test & sodium in the oil BEFORE the overheat back in 2011. So that (head gaskets leaking) had started even before the overheat.
My recommendation:
Clear hose test
Used oil analysis

 

[Chris Harrington]

Need your engine serial number to help confirm yours has these items but you may want to try thoroughly inspecting the thermostat poppet valve and especially exhaust check valves at the bottom as they have been found to make the engine run hot if not working properly.

Item 11 and 15,

Thermostat and Housing, Standard Cooling​

Thermostat and Housing, Standard Cooling

www.mercruiserparts.com

Item number 19,

Exhaust Manifold and Elbow​

Exhaust Manifold and Elbow

www.mercruiserparts.com

350 MAG MPI ALPHA/BRAVO EC - 1A300000 THRU 1A611927 and MORE​

350 MAG MPI ALPHA/BRAVO EC - 1A300000 THRU 1A611927 and MORE

www.mercruiserparts.com

 

[Chris Harrington]

Need your engine serial number to help confirm yours has these items but you may want to try thoroughly inspecting the thermostat poppet valve and especially exhaust check valves at the bottom as they have been found to make the engine run hot if not working properly.

Item 11 and 15,

Thermostat and Housing, Standard Cooling​

Thermostat and Housing, Standard Cooling

www.mercruiserparts.com

Item number 19,

Exhaust Manifold and Elbow​

Exhaust Manifold and Elbow

www.mercruiserparts.com

350 MAG MPI ALPHA/BRAVO EC - 1A300000 THRU 1A611927 and MORE​

350 MAG MPI ALPHA/BRAVO EC - 1A300000 THRU 1A611927 and MORE

www.mercruiserparts.com

I’d do the clear hose test to check for combustion gas getting into the cooling water from possibly leaky head gaskets. Temporarily replace the hoses feeding the manifolds from the thermostat housing with clear reinforced hose. Ideally test in the water & run it at idle & on plane while a helper watches for bubbles in the water flow. You can get more years from a raw water cooled engine in salt if you identify the cause & repair what’s needed. Might need new head gaskets & cyl heads inspected. I was able to do that with my old 4.3. Overheat damage from 2013 caused blown HGs in 2016. Fixed it that winter/spring of 16/17. But…I was getting bubbles in the clear hose test & sodium in the oil BEFORE the overheat back in 2011. So that (head gaskets leaking) had started even before the overheat.
My recommendation:
Clear hose test
Used oil analysis

Talked to my mechanic and although he's never done the clear hose test he'd like to do this as now we're starting to look at engine issues versus cooling system now that we've changed everything. Anybody have a link to a good video for instructions on the clear hose test to send my mechanic?