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HELP! Cylinder 5,6,7,8 getting water in them


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2009 wakesetter. Monsoon 350 engine. Ok guys I need a little help here. Took the boat out for the first time a few weeks ago, and noticed I had a heck of a miss. I done all the preseason upkeep and ran on a fake-a-lake to get oil changed and all that good stuff no issues. Get out on the water and the plastic 90 on top of the exhaust manifold melted and broke off. Got it back home and replaced that with brass fittings instead of plastic. Take the boat back out and it runs good for a little bit and then the it seems like it’s trying to hydro lock every time I go to start it but it will eventually start. Then the boat starts missing. Pull the spark plugs out and find that cylinder 5,6,7,8 all have gotten water in them and fouled my plugs. 5 and 6 had the most wAter. Took the boat back to the shop and took all the plugs out and blowed water out. Filled up with wd40 and all that good stuff. Done a little research and found that the flaps on the exhaust could be the issues. So being the fastest and cheapest I changed them. New plugs and oil, took the boat back out hoping that fixed the issue. Boat ran good for about 5 minutes after putting in the water and then it starts missing again. So apparently the flaps didn’t fix my issue. What all else could I possibly be looking at here? My next course of action would be taking the exhaust manifolds off and checking for cracks in the water jackets but how common would that be to crack in the exact same spot on both manifolds? Because I had no water at all in the back 4 cylinders, only in the front 4. Just doesn’t seem like something that would both go bad at the same time. Please and thanks for any feedback. This is my first time posting on here but I’ve found a hell of a lot of knowledgeable people just reading thru other posts here. 

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You have a cooking water flow issue if your manifolds got hot enough to melt plastic. First thing to check is an exhaust obstruction. 

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And then check the raw water impeller, remove debris from the transmission cooler, and change the thermostat.

You might want to change that 90 back from brass to plastic.  It's your canary for the coal mine.

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32 minutes ago, UWSkier said:

You have a cooking water flow issue if your manifolds got hot enough to melt plastic. First thing to check is an exhaust obstruction. 

When it was hooked to the fake lake I had good water flow coming out of both sides of the exhaust. Is there any way to actually check pressure on the exhaust or it’s just take it apart and try to find something? The engine has never attempted to overheat so I didn’t figure it would be an issue like that but I will check. I plan on taking the manifolds and all that off tonight. 

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11 minutes ago, justgary said:

And then check the raw water impeller, remove debris from the transmission cooler, and change the thermostat.

You might want to change that 90 back from brass to plastic.  It's your canary for the coal mine.

Yeah I didn’t think about it being something like that, that a good point. I honestly just assumed it was poor design, or had something to do with if someone used it for salt water or something. 

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9 minutes ago, Devan said:

When it was hooked to the fake lake I had good water flow coming out of both sides of the exhaust. Is there any way to actually check pressure on the exhaust or it’s just take it apart and try to find something? The engine has never attempted to overheat so I didn’t figure it would be an issue like that but I will check. I plan on taking the manifolds and all that off tonight. 

Your garden hose has pressure, but the raw water pump normally has to lift water to pump it through the system.  Also, idling your engine in the driveway will not heat it up nearly like driving the boat around will.

Start at the water intake and make sure it is clear, then move to the strainer (if you have one), then the raw water pump, then the transmission cooler.  At each part, ensure that the hoses are in good condition and have absolutely no possibility of letting air in.  The pump will greedily suck air through a tiny leak before it lifts water.

Rather than pull the manifolds, perhaps just remove the exhaust hoses if you can get them off.  Carefully inspect for damage to your catalysts and the inside of the exhaust hoses.  You may also want to do a compression test to see if you blew the head gaskets, which is very probable since you had water in the cylinders.

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Posted (edited)
2 hours ago, justgary said:

Your garden hose has pressure, but the raw water pump normally has to lift water to pump it through the system.  Also, idling your engine in the driveway will not heat it up nearly like driving the boat around will.

Start at the water intake and make sure it is clear, then move to the strainer (if you have one), then the raw water pump, then the transmission cooler.  At each part, ensure that the hoses are in good condition and have absolutely no possibility of letting air in.  The pump will greedily suck air through a tiny leak before it lifts water.

Rather than pull the manifolds, perhaps just remove the exhaust hoses if you can get them off.  Carefully inspect for damage to your catalysts and the inside of the exhaust hoses.  You may also want to do a compression test to see if you blew the head gaskets, which is very probable since you had water in the cylinders.

Would that not cause the engine temp to also overheat too if there was an issue from the raw water pump to the engine? The engine itself doesn’t overheat with the fake lake or actually on the water at full speed. The exhaust is the only thing that has apperently gotten hot. And the day that it blowed that plastic 90 out we rigged it up on the water enough just to limp it back. It the manifolds themselves didn’t feel like they were any warmer than they should be. I’ll still check all of that but it just seems as if that would cause engine over heating also

Edited by Devan
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On a vdrive you will get water from both outlets even if only one bank is getting proper flow. It dumps into the silent rider and flows from that down both legs. 

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45 minutes ago, UWSkier said:

On a vdrive you will get water from both outlets even if only one bank is getting proper flow. It dumps into the silent rider and flows from that down both legs. 

Very good point. I’ll check all that also. Thank y’all for the input 

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8 hours ago, Devan said:

Would that not cause the engine temp to also overheat too if there was an issue from the raw water pump to the engine?

This is known as a bad impeller and a blocked transmission cooler.  See above.

The cooling water cools the engine and then everything dumps to the manifolds.  If they are hot, you don't have enough water flowing.

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12 hours ago, justgary said:

This is known as a bad impeller and a blocked transmission cooler.  See above.

The cooling water cools the engine and then everything dumps to the manifolds.  If they are hot, you don't have enough water flowing.

Ok thanks. So as far as root cause I’ve got stuff to check. But as far as what it could have caused to be getting water in the cylinders. Head gasket is the only thing you guys are thinking it could be?

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1 minute ago, Devan said:

Ok thanks. So as far as root cause I’ve got stuff to check. But as far as what it could have caused to be getting water in the cylinders. Head gasket is the only thing you guys are thinking it could be?

Head gaskets or cracked block or maybe bad intake gaskets.

Edited by oldjeep
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2 hours ago, oldjeep said:

Head gaskets or cracked block or maybe bad intake gaskets.

Or bad riser gaskets, but that would only apply to two-piece manifolds.  I expect that an '09 has ETX aluminum manifolds. 

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2 minutes ago, justgary said:

Or bad riser gaskets, but that would only apply to two-piece manifolds.  I expect that an '09 has ETX aluminum manifolds. 

Actually that is another possibility - internal cracks in the ETX manifold could cause that, but they would both need to be cracked with there being water on both sides of the engine.

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6 minutes ago, oldjeep said:

Actually that is another possibility - internal cracks in the ETX manifold could cause that, but they would both need to be cracked with there being water on both sides of the engine.

Good point, since the issue could have been caused by improper winterization if it wasn't just a bad impeller.

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