2003 Mercruiser 6.2 MPI Exhaust Manifold cracks

[SS Annabelle]

Hi Everybody,
Hoping somebody can help us diagnose our exhaust manifold issues.

When we first took out the boat, she ran great!! However, we did not turn the engine off at all on that trip.

The second time we took the boat out, we sat on the water for a bit with the engine off and that is when our troubles started.

The boat runs great until you turn the engine off and when trying to start it back up there is a loud grinding noise and sounds like everything is breaking. At this point we are hydro locked (every time).

The first time we started having issues we replaced: the starter, alternator, and first New exhaust manifold. We found that exhaust manifold had a large crack in it, which would cause water to pool in the exhaust manifold, in the oil and spark plugs. Each time the spark plugs are pulled, we find the water on the Port side, middle chamber.
We also, performed a compression test on each of the 8 spark plugs to make sure there was nothing wrong with the engine itself. We found no issues with this series of tests.

Took the boat out and she ran great!! Until we turned off the engine. Once again we hydro locked.

We pulled the spark plugs (water came out of same place; port side, middle chamber), checked the oil and checked the manifold and once again... water in everything.
We assumed this time that we had a defective exhaust manifold and sent it back to the dealer to request for a replacement.

We replaced the New exhaust manifold with the second replacement. Found the same issues and hydro locked again.

This time we decided to purchase a New OEM manifold. Came up with the same issues.

We have tested the Elbow and Riser on the Exhaust Manifold and they seem to be fine. The Exhaust Manifold on the Starboard side of the boat is just fine and we have not had any issues with it. We have also found that the Exhaust manifold cracks in the same place every time. We have found this out by pouring Acetone where water would flow and putting corks in to provide a small pressure test. Also, there has been no visual indication that the boat is over heating. The gauges have all been fine and the Elbow, Riser and Exhaust Manifold have all felt cool to the touch and not hot.

So far we have replaced:
Spark Plugs
Spark Plug wires
Distributor Cap & Rotor
Replace Oil and Oil filters several times
Starter
Alternator
2 New Exhaust Manifolds along with gaskets
1 OEM Exhaust Manifold along with gaskets

Hopefully with all this information, someone could help us.

 

[alldodge]

Howdy

Dang you sure got an issue going on. What is your serial number and do you have risers and elbows on the manifold or just elbows?

 

[SS Annabelle]

Engine serial # OM616163. Yes, we do have risers and elbows. We have tested those and they are fine.

 

[alldodge]

Closed or raw water cooling?
When was the last time the raw water pump was inspected and impeller replaced?

 

[SS Annabelle]

Raw water cooling.. We have tested the water pump and it seems to have an adequate amount of water flowing. The engine has never over heated or risen to high temps. The exhaust manifold, riser and elbow have always felt cool and have never felt hot.

 

[alldodge]

While not certain I'm leaning toward lack of water. Don't know for sure but the 7.4 and 8.2 had issues with injector on cylinder 7 (3-back port side) of running leaner then the others. This was caused by the intake port was not as large as others. Not that this is the issue it may only be a contributing factor. If your not getting enough water to port then starboard this could cause things to get a bit hotter. That said you also have risers which should cause the manifold to be full of water.
Thermostat housing, The check balls (item 14) have been known to hang



The 7 point drain system,

 

[Bt Doctur]

unless there is a bad batch out there, have never seen a crack in that area. the floor bottom, yes.
only other thing that comes to mind is the mounting bolts are a bit too long and crack the housing when you install them.

 

[alldodge]

Well crud just noticed I posted the same pic twice. Here is the 7 point

 

[SS Annabelle]

Good Afternoon!!

We checked into the thermostat and have attached the picture of the one that is on our boat. Do you have any advise for this thermostat?

Also, we checked into the bolt size and they measure correctly.

Thank you for your help!!

 

[alldodge]

That housing is for the 3 point drain system, and that system is a rats nest of hoses IMO. You could have flow problems just from all the hoses. The pic has the part number and size


Thinking your problem could be in this area, if what is not going out thru the exhaust but circulating back around. Could even be where all the fittings come together at the bottom

 

[SS Annabelle]

Well.. we pulled the Distribution Housing and the part the you have circled does not apply to our water flow. There is a cap where that straight line would be. I have attached a picture of what ours looks like. In taking all the hoses off, they all seem to be fairly clean.
We also, pulled off the thermostat. I have attached a picture of that as well.
Any advise as to where to look next??
We have decided to name our boat.. the "Trailer Queen".. haha

 

[alldodge]

My thought is you have some kind of a restrictive water flow to the manifold and that spot in the exhaust is getting to hot. I can see from the thermostat housing that it looks it good shape and the correct gasket is being used (brass rivets). What gives me concern is you have the housing for the 3 point drain system but you stated you don't have the tee fitting and hoses. I'm wondering if some hoses have been capped off or removed. As this is the first time I'm seeing this issue, with parts missing from what should be there it gets me wondering.

How long have you had the boat and do you have item 9 listed in the pic above? The one which has all the hoses coming into I?

 

[SS Annabelle]

I am sorry, I may have confused you. I have attached a picture of what our system looks like, with a few notes of what we do not have.

 

[Bt Doctur]

Personally I would eliminate the single point drain system entirely.Too easy to get a cracked block if the block fittings gets clogged.
remove everything and plumb the hoses for raw water cooling.

 

[alldodge]

With free flowing water as we know it flows the path of least resistance. My thought remains that somehow the manifold is not getting sufficient water to it. From the hose routing the risers and manifold is getting water but the amount is probably the issue. Could be getting more in the riser and elbows and not enough in the manifold. It needs unrestricted flow through the drain, past the water circulating pump and then thru the thermostat housing just to get to the manifold. Need more water going in thru the bottom of the manifold then into the riser to keep them cool. I'm spit balling here, not saying this is being done just see there is not enough water.


I like the thought of the single point drain but ever since they brought these out I can see nothing but problems with the later. If it were mine I would be thinking real hard about going to the seven point drain

 

[Bt Doctur]

just serviced a 29 sundancer with e the flushing setup. both block inlets/drains were plugged solid.The 2 boats I service with this type of system ,I remove the quick connect and probe the drains.Have yet to find that they remain open for draining after a season`s use.

 

[mart284]

I have now reached to the point where I have replaced manifolds four times and each time I hoped that I found the reason for it.. Firstly I blamed old age of the engine and put new manifold, after 2 hours of driving, another crack, then changed the provider .... and after another crack also managed to hydrolock the engine. Removed the engine, took it to pieces, replaced bent parts and found out that gasket between block and head was not correct one and was leaking gases our. Sent both head to service and got them both back, measured everything and put everything back. 2 hours later I have again water in the same side of the engine. It all started after fixing small oil leak in the wither and this summer has been a nightmare. Does anyone know how this was fixed in SS Annabelle's case?

EDIT: Boat is Sea Ray Sundancer with V drives from 2002, for some reason I can not add pics here..

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