Opinions requested for likely cause of water intrusion into cylinders (with pictures)

[rodgeml1]

Engine: Mercruiser 4.3L Reman

I purchased a remanufactured engine online (I know...first mistake) and installed it onto my boat. Everything worked fine until about 15 hours of run time. I was coming off of plane and just as I got to idle a loud, rhythmic knock could be heard from the engine. I increased the RPMs with the boat out of gear and, not surprisingly, the knock followed right along. Rather than tear the engine apart to determine the problem and risk destroying any evidence that the engine had a defect, I pulled the engine from the boat and sent it back to the remanufacturing shop from which I purchased it. The shop pulled it apart and said the only problem they found was there was water in one of the cylinders and told me that my risers and/or manifolds were bad. I had him take some pictures and send them to me and it's clear there was water in four of the six cylinders (pictures are below). The pictures that shows just one cylinder rusted also appears to show a leak path across the head gasket. I separated my risers and manifolds for a look but couldn't find any evidence indicating that's where the water came in (pictures of those are below). So, do these pictures indicate the water came from the risers/manifolds? I'm surprised the engine was even running with water in four cylinders.

 

[alldodge]

Engine: Mercruiser 4.3L Reman

I purchased a remanufactured engine online (I know...first mistake) and installed it onto my boat. Everything worked fine until about 15 hours of run time. I was coming off of plane and just as I got to idle a loud, rhythmic knock could be heard from the engine. I increased the RPMs with the boat out of gear and, not surprisingly, the knock followed right along. Rather than tear the engine apart to determine the problem and risk destroying any evidence that the engine had a defect, I pulled the engine from the boat and sent it back to the remanufacturing shop from which I purchased it. The shop pulled it apart and said the only problem they found was there was water in one of the cylinders and told me that my risers and/or manifolds were bad. I had him take some pictures and send them to me and it's clear there was water in four of the six cylinders (pictures are below). The pictures that shows just one cylinder rusted also appears to show a leak path across the head gasket. I separated my risers and manifolds for a look but couldn't find any evidence indicating that's where the water came in (pictures of those are below). So, do these pictures indicate the water came from the risers/manifolds? I'm surprised the engine was even running with water in four cylinders.

The cylinder head does show that water was present enough to cause rust. If this was before or after the fact I cannot determine. The gasket of your riser (elbow) shows no signs which I can see that would indicate an issue. What I don't see is your manifold exhaust ports. What do they look like?

 

[rodgeml1]

The cylinder head does show that water was present enough to cause rust. If this was before or after the fact I cannot determine. The gasket of your riser (elbow) shows no signs which I can see that would indicate an issue. What I don't see is your manifold exhaust ports. What do they look like?

Do you mean the ports that mate to the head? They looked clean. I'll take pictures of them tomorrow and upload them.

 

[alldodge]

Do you mean the ports that mate to the head? They looked clean. I'll take pictures of them tomorrow and upload them.

Yes the only way to get water into the cylinders is either the manifold, elbows or the exhaust shutters in the Y-pipe. If you stop quick and the shutters are missing or not working correctly water can get ingested. The knocking is an issue and if water was ingested you could have bent a connecting rod

 

[thumpar]

I think the engine builder is probably right in this case. Your manifolds or risers may have failed. From the amount of rust it looks like you are boating in salt. The exhaust parts are normal maintenance parts in salt.

 

[rodgeml1]

Yes the only way to get water into the cylinders is either the manifold, elbows or the exhaust shutters in the Y-pipe. If you stop quick and the shutters are missing or not working correctly water can get ingested. The knocking is an issue and if water was ingested you could have bent a connecting rod

I checked the shutters in the Y-Pipe before I dropped the engine back in and they worked fine. I'll check the manifold ports for evidence of water getting in there.

 

[rodgeml1]

I think the engine builder is probably right in this case. Your manifolds or risers may have failed. From the amount of rust it looks like you are boating in salt. The exhaust parts are normal maintenance parts in salt.

Wouldn't the manifolds/risers show evidence that water came in through there? I can't find any evidence of that. Also, one of the pictures shows rust on the head of just one cylinder. That's not likely if water came in through the manifold is it?

 

[alldodge]

Wouldn't the manifolds/risers show evidence that water came in through there? I can't find any evidence of that. Also, one of the pictures shows rust on the head of just one cylinder. That's not likely if water came in through the manifold is it?

The pics shown show rust on Edit four cylinders.

We are working from your pics and if the water did not come in through the exhaust, the next place would be the intake manifold. As before I'm seeing rust on four cylinders. One on one side and three on the other

 

[Lou C]

One of your exhaust pix clearly shows rust trails in the exhaust gas passage of the manifold or riser. Look at the last two pix, if its the riser it looks like it sucked water up the exhaust. Does the boat sit low in the rear? The gasket looked good, but what does the sealing surface look like?