Mercruiser 5.0 MPI Hydrolocked

[IM Buddy8]

Hello, thanks in advance to anyone that can help me out!

Took the boat out two nights ago, it started at the dock no problem (I always start it when I get there just to be safe) we then hung out at dock for about 2 hours, went to go out and it was cranking pretty tough and made some harsh noises doing so. Tried again and it did eventually start and seemed to clear up and ran fine we went out about 15 min ride it idled, set the anchor and shut off engine. Immediately started it right back up to make myself think that it was now good to go and would start when we planned on going back to dock. Well 4 hours later, went to start very hard cranking to a point where it was "softly" locked up. Stopped trying of course and called for a tow.

Today before trying to start it again I pulled plugs (planned to put a scope inside to see if there was any evidence of water) but when I pulled the starboard side plugs it was obvious that there was water in all four of those cylinders (seemed like most of the water was in the 2nd from rear (#6). It cranks over and doesn't make any horrible noises as I was purging that water out all seemed ok in the bottom end at least.

So, water is getting in there, it is an 03 so the exhaust is the dry joint style, but is it still common for the manifolds/risers to fail and allow water to get into the cylinders on the dry joint ones?
Could it be the exhaust flaps that stop water from coming in on decel? (it came to an idled stop like normal when we anchored out so I don't think this is it but not sure).
Could it be the head gasket on the starboard side?

Those are my three ideas:
1. Risers/Manifold
2. Exhaust Flaps
3. Head gasket

What are the appropriate steps to diagnose properly to figure out if it's 1,2,3 or a combination of them causing the issue? What's the likelihood that the block is still good? It seems ok but I also don't know if it were hydrolocked if that would kill the head gasket as well.

Then if you have any recommendations of where to get the parts from (would like to get this done ASAP) that would be helpful thanks!

Random question that might be a stupid one, can I do the exhaust flaps when in the water, or could water come in through there when I take off the elbow that goes down to them? The boat is in the water at my marina and I'd like to avoid pulling it out of water.

 

[alldodge]

First pull the kill switch (keeps motor from starting) remove all plugs and spin the motor over with plugs removed to flush water out. Spray fogging oil into each cylinder and spin over some more.

If your in salt water then its way past time to do the exhaust (about every 7 years)

If your in fresh water then did the motor ever over heat?

Normally the flappers can be replaced in the water. This all depends on how deep the stern sits. To determine if it can be done loosen the hose clamps furthest away from the Y pipe. Once loose use a hose pick or screw drive and push between hose and pipe. If it starts to leak then it can not be done

 

[Bondo]

Those are my three ideas:
1. Risers/Manifold
2. Exhaust Flaps
3. Head gasket

Ayuh,...... I would guess, the exhaust manifold, or a cracked head, by yer description,....

I'd pull the manifold/ riser, 'n inspect it,......
If it's not the problem, air pressure test the drained block, with the spark plugs out, 'n listen,.....
If the head is cracked, you oughta be able to hear it,......

Vortec heads are known to crack in the exhaust bowl area,...... thin castings,.....

 

[IM Buddy8]

Ayuh,...... I would guess, the exhaust manifold, or a cracked head, by yer description,....

I'd pull the manifold/ riser, 'n inspect it,......
If it's not the problem, air pressure test the drained block, with the spark plugs out, 'n listen,.....
If the head is cracked, you oughta be able to hear it,......

Vortec heads are known to crack in the exhaust bowl area,...... thin castings,.....

Thanks, do they crack when under normal use and operating temperature or does it usually require an overheat to crack one? It's never overheated in the almost 2 years I've owned it that's why I ask.

 

[IM Buddy8]

First pull the kill switch (keeps motor from starting) remove all plugs and spin the motor over with plugs removed to flush water out. Spray fogging oil into each cylinder and spin over some more.

If your in salt water then its way past time to do the exhaust (about every 7 years)

If your in fresh water then did the motor ever over heat?

Normally the flappers can be replaced in the water. This all depends on how deep the stern sits. To determine if it can be done loosen the hose clamps furthest away from the Y pipe. Once loose use a hose pick or screw drive and push between hose and pipe. If it starts to leak then it can not be done

I'm not sure how old the exhaust is, but I'm in saltwater so it's probably time to change it all. I will also buy flappers in case those are old I'll replace to be safe as well. Hopefully it's above the waterline at that point!

 

[Rick Stephens]

Be careful doing that in the water. You have extra tall risers, done because the motor sits low in the water. Don't sink the boat.

 

[Bondo]

Ayuh,..... Good catch Rick,...... Normally, without the riser extensions, the water level is pretty much right at the shutters,......

 

[Searay205]

99% sure the exhaust side of your manifold corroded through. Remember on the back side of the exhaust you have water vs combustion temperatures. erosion corrosion. Pull risers and manifolds look in exhaust passages you will see a crack, then take sledge hammer and bust manifold apart you will see they are paper thin.

 

[Searay205]

You didn't include year and those are not cat manifolds so older than 2011 YOU NEED NEW MANIFOLDS AND RISERS especially in brackish or salt water

 

[alldodge]

Be careful doing that in the water. You have extra tall risers, done because the motor sits low in the water. Don't sink the boat.

Agree, good catch

 

[IM Buddy8]

Thank you all for your recommendation, unfortunately I'm still in quite a tough spot.. So today I bought and installed all new OEM of the following on both sides of the motor (even though only one side had water in cylinders):
Risers
Exhaust Manifolds
Manifold gasket
Riser Extension Gaskets
Plugs
Wires
Cap/Rotor
Oil change
Exhaust Flappy things (old ones actually looked fine and were intact, but replaced anyways)

When I finished I started it up, it took a little throttle initially but then once it was "cleaned out" it ran perfect at idle and seemed fine when I revved it in neutral. No crazy knocking noises or anything. There was a whistle noise but that seemed to go away. Let it get up to temp (170) and it seemed thermostat was working and it was running at the right temp and idling/running very nice.

Shut it down, started it back up and it started no problem. Waited 40ish minutes while cleaning up, went to do one last start before going home and it had started to slow crank and I could tell the same thing it was hydro locking the starboard side cylinders! Shut the key off and went home. What could be filling all cylinders on that side? Definitely not the flaps because the boat is in a marina that's behind a hurricane barrier so there is almost no movement and no one was making a wake today when leaving the marina.

It almost seems like it's fine when running, but then when it sits off for a half hour or more it's slowly filling cylinder(s) on the starboard side of the engine. What the heck could the cause be, it runs perfect when it's running I bet if I take those plugs out crank it over to get the water out put plugs back in it will run fine all day until I shut it off and let it sit.

Any additional help would be greatly appreciated!

Best,
Ryan

 

[alldodge]

Possible intake or head crack, or head gasket

 

[Searay205]

did you see any crack in the manifolds you removed? get a good light and really study the exhaust passages. you might even see corrosion. if you want with safety glasses bust them apart and see how thinned they are.

 

[Rick Stephens]

Salt water boat. Wonder if you have a hole corroded through in the internal water jacket somewhere. Internal on your motor looks nice enough to call new.

 

[Josh83]

What ended up being the issue? I am having the same problem and have replaced everything you did as well. I’m at a loss
Thank you

 

[jbcurt00]

What ended up being the issue? I am having the same problem and have replaced everything you did as well. I’m at a loss
Thank you

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