2015 Motor MerCruiser 4.5L 250hp NO EC - OVERHEATING!

[leosmdp]

If anyone can help or give any tips about this project I would be more than welcome!
Could find too much info about this motor on the web so I posted this maybe it will help others like me in the future!.
I bought this boat used in a deal for a guy who I guess notice the condition never had made a flush in the system in this poorly but nice 2015 Motor MerCruiser 4.5L 250hp NO EC- ( this model doesn't have a Heat exchanger and raw pump in the same motor belt) I guess this is the oldest version this kind of motors.
The Motor has 105 HS. I bought a Vessel View and checked. Compression Ok Start at the moment.
The problem Overheating (I just drove it to the ramp (for about 15 min) and nothing came as a fault in the system) Noticed Water Temp was around 160 degrees, Oil was old, and wanted to damage nothing.

After I read a lot and nutrient my brain with any kind of info started to disarm the whole water system.
1- found rust sediments in HOSES so I pressed hard with my hand and cracked the glued metal sediment fragments inside the hoses' walls and flushed
2- I noticed that the RISER AND MANIFOLD were in good condition. I flushed them with fresh water, and put today in them Ospho Surface Prep. (they don't have any cracks on the walls inside and the outside are solid ) , any other rust treatment surface product to recommend?, I know is better to change it but I don't have 2600 right now
3- FLUSHED every single hose outside and put a hose inside the motor as well to clean it.
4-WATER PUMP cleaned it look ok twist smoothly (couldn't disarm cuz it doesn't have nuts in the back)
5- THERMOSTAT(I tried it in hot water and opened, it in good condition ) but it was dirty and rust cleaned.
6-POPPET VALVE was fully of rust sediments (Photo) with signs of use beginning of material fatigue over the rubbers ( so i changed the DIAPHRAGM and origins)

So i didn't yet disarm the steam drive but is a Mercury Alpha Gen 2 where the raw impeller is located (I order a new one as well)
I will change the spark plugs, oil, oil filter, fuel filter, gear lube....

If any mechanic over there can give me more tools to check before putting everything on it would be more than welcome.
Cheers!

 

[alldodge]

Welcome
It looks like your on the right track to stop the overheating

 

[leosmdp]

Thanks alldodge for your only reply!
I did the whole process, put everything right with torque on manifold and riser (tested outside with good water flows ok) (38 nm), new sparks plug gap 0.51 (20nm) , new anodes, new pcv.
New raw water pump complete on the alpha gen 2 sterndrive.

BUT yesterday I went to try it after a lot of work completed and it gave me the SAME PROBLEM. ENGINE GUARDIAN CUT THE POWER //. I made a slow (At 1500 rpm ride / temp always at 180 with top of 230 here with the guardian)
521-20 ENGINE STBD ( ENGINE COOLANT TEMPERATURE STARBOARD )
A TEMP SENSOR CALUE IS HIGHER THAN NORMAL

The only thing that did not change was the thermostat (I tried it in boiling water and it opened at 140 degrees) I will order for a new one anyways.
And the thing was circulating water pump that I observed and it turned well but I no longer have more resource to do.

I posted some temp reads with gun temp
I noticed in the crossover connection hose difference temperatures.

If anyone can help me or recommend a mechanic to solve this here in Fort Lauderdale zone.

attached several photos

 

[leosmdp]

here I posted the gun temp checked during the test.
manifold always maintains the same temp on hot.
but the difference came from the crossover hose from one side port is 150 and the other 190!. before hitting the 220 error.

 

[Lou C]

Ok it’s hard to say but from the pix I’m wondering if the water passages in the exhaust manifolds & elbows are clogged. They don’t look corroded but I’d hook up a garden hose to them & see if they flow well & flow the same each side. Those temps seem really high seeing as how the engine is at idle with no load on it.
I’m not totally understanding why your thermostat housing is so hot either. Normally the housing is cooler that that since the stat opens at 140*. Unless it is opening too slowly or not all the way.
One thing that is a cause of mysterious overheating is a leaky head gasket causing combustion gas to get into the cooling water from a leaky head gasket. I wonder if that’s happening on the cyl head that feeds the side of the cross over that is at 190*?

 

[leosmdp]

Lou c, yes I feel the same but I don't know where?.. when I took out manifolds and risers I cleaned as much I could I put the garden hose in every hole and water flows right... hoses I already cleaned, poppet I change the diaphragm and also made a test with water
I didn't change the thermostat (already ordered a new one), the circulation water pump and the T in the bottom of the manifold (FITTING ASSEMBLY) I do not know the actual function but water comes when I tested with the garden hose.

 

[Lou C]

Again I'm not familiar with these newer Merc engines and the cooling system is a lot more complex than the older models. However, on the old models the way you would test for leaky head gasket putting combustion gas into the cooling water, was to replace the hoses feeding the exhaust manifolds with clear hose. Then put the boat in the water (for a valid test) and run it at idle, and after warming up, above idle. If you see bubbles in the cooling water stream going to the manifolds that could be a sign that a head gasket is leaking allowing hot combustion gas to heat the cooling water.
We had a Subaru Outback with the EJ 2.5 flat four engine that did this, twice. When the head gaskets on these blow, the don't put antifreeze in the oil, they put exhaust gas in the cooling system and cause episodic overheating at higher speeds. The cure was new head gaskets.
I have a relative who owns a boat with the new Merc 4.5 200 hp but he has not had any problems with his like this. It runs at a cool 140* all the time. Even in salt water.

Last thing I can think of, it has cat converters, correct? I thought I saw that in the manifold and saw the O2 sensor on the exhaust elbow....on cars if a cat converter clogs up or goes bad it will obstruct the exhaust and overheat the exhaust system. Not sure if Merc's system is the same as automotive in that respect.

 

[leosmdp]

Thanks again Lou, I will do that as well. yesterday I saw on YouTube a mechanic who recommend put clear hoses to check the system (he found that the problem was the circulation water pump cracked (but his error was a sudden change from 70 to 190)).
the test I made yesterday was on the ocean I didn't force the motor always less than 3000 rpm and after the error at continue 1600 rpm // temp 185.
motor is 107 hs.
Any kind of help, no matter how small, will be welcome...

 

[leosmdp]

Lou
the Catalytic thoroughly cleaned the manifold riser and catalytic (with acid ospho and later neutralized with baking soda..) i put a garden hose and the water flows ok after assembling everything.
Things didn't go well I changed the thermostat, and nothing changed.
I replaced the hoses from the crossover to the manifold for clear and notice that from the crossover to the manifold travel only gas when is on the motor not water I don't know if this is correct..(when I stop the motor water came from this duct) ( From N to M on both sides)
I will put today a clear hose 2 1/2 from the pump to the hose assembly ( FROM J to I ).
and from the thermostat to the hose assembly. ( FROM M TO I)
i still didn't replaced the circulating water pump (another 350 ...) but she move smoothly and was ok when i disarm (couldn't see the impeller inside cuz is sealed the assembly)
that's my last shot may be as you told me are the head gaskets. but before disarming I need to make sure (is a huge work).. or call a mercury-certificated

 

[Lou C]

Ok let me make sure I'm understanding what you're saying...you get air bubbles from the hoses marked in blue from the cross over to the manifolds when the engine is on, but water flows when you shut it off? Now one thing with this test, is it can be inaccurate if done with the water muffs on land because those can suck in air. It is most accurate when the boat is in the water and the outdrive is sucking in water via the water intakes like in normal operation. If that's the case, I would check for water in the motor oil or water in cyls, both can happen with leaky head gaskets but not in every single case.

On my engine I had a bad overheat about 10 years ago. After that it seemed fine, I replaced the burnt up parts in the exhaust system, and it ran fine (good compression, no obvious water in the oil) for 2 more seasons. At the end of the 3rd season, it started with hard starting, some water in 2 cyls and water in the oil. I pulled the boat and rigged up a way to test that (a little different than the clear hose test) what I found was that exhaust gas was definitely getting in the cooling water and would seep into 2 cyls when the engine was shut off. I took it apart and it was definitely both head gaskets blown from the overheat, and both heads had cracks in the center cyls exhaust seat. I rebuilt it with reman heads, new gaskets and new cyl head bolts. Took a while but not a hard job.
The teardown:

reman heads installed, hydraulic lifters adjusted, ready to be put back together....

 

[Lou C]

Also, believe it or not, this Merc 4.5 that you have, really appears to be an adaptation of the old GM 4.3 V6 you see in my pix. Yours has a balance shaft, slightly modified cyl heads and a modern EFI system but the basic design is very very similar. The one down side is that engine parts come only from Merc and are like 2x--3x as much as standard GM engine parts. So repair cost wise they are similar to outboards now.
#7 in your pic seems to be some kind of fuel cooler, that was also used on other Merc EFI engines.
For my use I really like the old school GM engines with simple electrical systems and carburetors.
They can be maintained and repaired for little money, as long as you understand old school systems. Like working on a classic car. I had cars with points ignition and carburetors (actually the same Quadrajet 4bbl) back in the '70s. They don't run as well as modern fuel injected engines but are far easier to deal with as far as repairs, parts cost etc.

 

[leosmdp]

Lou let me explain better, the test I made it with fresh water and in the place where I parked the boat with a garden hose connected to Dual Flow Rubber Motor Flusher attached to the alpha sterndrive. yes maybe is sucking air but still only hot air comes out from the crossover to the manifolds (both sides) when the motor is on, and when the motor is off water back from the manifold, and throw the hose to the crossover. ( in these hoses should travel water or compression air?)

Today I will put those 2 1/2 clear hoses to see if water flow at least to the thermostat I'm not a mechanic as you can notice ...
The motor has great compression and turns on without any effort at all.
it has no evidence of water in the system.
I changed the engine oil and it didn't have any water either.

but I bought it with the overheating problem and... yes could be the head gasket burned from the last and only owner...
Thanks for your time and effort to explained me, im a rookie in this subject.

 

[Lou C]

Ok I’d like to see you do the same test with the boat backed into the water. That way no confounding variables like sucking a bit of air which can happen on the water muffs.
BTW the only advance warning I got on my engine before I had water in the cyls was when I did a Blackstone oil analysis (in 2011, and 2015). Both showed sodium (from salt water) in the oil which indicated that water was getting in the oil (but not enough to show on the dipstick) . The overheat was in 2013. So the head gaskets were actually starting to leak even before the overheat.
I did 2 oil analyses (2021& 2022) after I fixed it & it was much better. No elevated sodium & wear metals like alu, iron & chromium all much lower. Water in the oil & high wear metals is not good for engine life.

 

[leosmdp]

Great info there! I just order the sample kit from Blackstone! to have more info and compare maybe in the future when this issue is solved!
(sadly I already changed the old oil and put in a new one last week)

 

[leosmdp]

I will run some tests today with a couple of flushes with salt remover maybe I will try with vinegar and Dawn soap (as I saw in YouTube)
I filled up a bin full of water to prevent air bubbles from entering the system.
(The hot water from the engine (hot) will not be received by this container to maintain a flow of water at 80/90 degrees F.)

 

[alldodge]

Two things not good

The impeller in the drive will have a hard time sucking up from a tub. The water needs to be at or above the level of the pump, so at least even with trim rams

One of the clear hoses is kinked.

 

[leosmdp]

alldogde thanks!, as you can see is also attached a garden hose connected to Dual Flow Rubber on the drive I only fill up with water to prevent some air suction. yes water is also above the impeller suction.
yes I note the kinked but was impossible to turn is sooo hard that hose, also that hose is bigger than the original I will run the test and keep posted.

 

[alldodge]

Thanks for clarifying

The red dots should only have moving water moving in them when motor is off and motor is being winterized (draining). The large one under the thermostat would have very little if any. Water comes up other hose to water circulating pump. This pump circulates water into block and back out

The check valves under each exhaust manifold keeps all water from flowing back once filled until draining is needed.

The poppet valves are there to restrict flow to elbows to make sure motor and mans stay full. Some water should exit but at a reduced amount. If poppet valves get stuck open then motor does not get enough cooling

The poppets are a bad design and have failed often

 

[leosmdp]

Professor Alldodge thanks so much for your time and the explication, to me and the rest of the people afterward to be taught. really helpful.
I made some tests after these new things were installed.. with the new thermostat, and the clear hoses (a bit bigger than the originals), and leave the motor from one day to another with some salt remover in the system (Star Brite Salt Remover) and in between the test, a couple of time flushed with it.

30 min at idle and I got not overheating .... woo hoo! So it was an improvement..!!
the max temp reached was 156....and the average was around 149 to 154. a bit high from 140.. but at least is not 220.
manifold/risers in hot always maintain the 210 to 214.

post 2 confused photos with the reading
First one after 3 min from the start when the thermo opened
Second 30 min later no big differences, so the cooling system is working...
I would love to see temperature readings of the same engine that works perfectly.

I need to put some rpm on it, now is time to real water test.

(note: yes, after sanding (3000 w/s) I painted with a clear coat the gauge. cuz was all scratched)

 

[alldodge]

A bit warmer at the thermostat is a good thing in salt water, it can help keep the salt build down, but not a lot.

I would suggest installing a fresh water flush so it can help keep it cleaner. I would use a couple of ball valves or webstone double valve, but only if you have bravo drives