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Merc 4.3 Water in Cylinders

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mike1970

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Happy 4th of July everyone!
I have a 1998 Merc 4.3 V-6, 4 bbl, rwc, Alpha One. Been having this ongoing problem since I got the boat 4 years ago. I purchased this and had the marina install new manis and risers(genuine Merc, not aftermarket) as well as some additional items.
I have been having a problem w/ water in the cylinders on an occasional basis. What I have been doing is after use, i would drain the mani's and engine to be safe. This latest time I did not drain anything, and about a week later, which was today, I went to crank it over, and is stopped. Pulled plugs, cranked over and got water out of # 2 &4. A lot of water in #4, #2 just damp. Pulled riser, found standing water in mani at #4 Thought mani to riser gasket could be bad, but found no evidence of leaking inside of manifold(streaking).
Did compression test #1-200;#2-170;#3-200;#4-230;#5-195;#6-190
Thought maybe a cracked block, head gasket, intake gasket or intake, so I pressure tested the cooling system to 20 lbs for 20 min, found no leaks and pressure did not drop, so if I am correct, that would eliminate the head, intake gaskets and the intake.This was done on a cold engine, unsure if a warm engine would change results.
I will fill the mani w/water tonight and see if it leaks into the exhaust side.
Does anyone have any ideas on this problem? Any help would be appreciated.
Thank you
 
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Sounds like a bad manifold. Does not matter if it is new. Get a piece of plywood and drill some holes in it to match the riser. Put a piece of rubber on it and bolt it over the riser port on the manifold. Pump the manifold full of air, about 10 lbs. Fill the exhaust ports full of water and look for bubbles.
 
Any chance you have thru transom exhaust or is it thru prop?

If thru transom this would be one possible reason.
 
I have a thru prop exhaust. I am thinking (and hoping) it's the manifold. I filled the water side w/ water last night and let it sit overnight, and this morning, the exhaust side is still dry- no leaking. I will try what Dockside recommended and pressure test it.
I had a similar problem with my furnace at home where it was fine cold, but as soon as it fired up, and got hot, water would leak thru the casting. Wonderin' it this might be the same problem
 
mike1970 said:
Happy 4th of July everyone!
I have a 1998 Merc 4.3 V-6, 4 bbl, rwc, Alpha One. Been having this ongoing problem since I got the boat 4 years ago. I purchased this and had the marina install new manis and risers(genuine Merc, not aftermarket) as well as some additional items.
I have been having a problem w/ water in the cylinders on an occasional basis. What I have been doing is after use, i would drain the mani's and engine to be safe. This latest time I did not drain anything, and about a week later, which was today, I went to crank it over, and is stopped. Pulled plugs, cranked over and got water out of # 2 &4. A lot of water in #4, #2 just damp. Pulled riser, found standing water in mani at #4 Thought mani to riser gasket could be bad, but found no evidence of leaking inside of manifold(streaking).
Did compression test #1-200;#2-170;#3-200;#4-230;#5-195;#6-190
Thought maybe a cracked block, head gasket, intake gasket or intake, so I pressure tested the cooling system to 20 lbs for 20 min, found no leaks and pressure did not drop, so if I am correct, that would eliminate the head, intake gaskets and the intake.This was done on a cold engine, unsure if a warm engine would change results.
I will fill the mani w/water tonight and see if it leaks into the exhaust side.
Does anyone have any ideas on this problem? Any help would be appreciated.
Thank you
Click to expand...

Just so you know, Mercruiser sells Cheap replacement manifolds and good quality ones. I my humble opinion, the cheap replacement manifolds from Mercruiser are just as crappy as GLM (good luck marine) In fact they look the same, except for the name.

Which do you have?
 
Find out what riser/elbow gaskets they used. Do some research and make sure they are the proper ones. Does the engine getting up to proper temp; 160 or so?
 
Just a little update: I pressure tested the manifold like Dockside recommended, pressurized to 50lbs, no leaks. Thought maybe that if it got hot, the leak would show itself, so I filled the entire mani w/ boiling water to heat it up, let it sit for about 5 min, drained it, refilled the water side w/ boiling water and applies 50 lbs of pressure, no leak, heated the exhaust side w/ a torch, still no leak, so I am guessing that there is no prob w/ the mani.
A mechanis at work suggested I pressure test the cylinders. He said that pressure testing the cooling system is fine, but that was only 20 lbs, the compression is around 190, so he said to test the cylinders w/ as much pressure my compressor would put out, in my case it is 140 lbs, that would hopefully eliminate the head gasket and block. So I filled the cooling system w/ water and tested the cylinders, and no leaks!!
I am at a loss!
So today, i re-installed the mani and riser w/ new gaskets test run and it runs fine as usual. So i drained the mani's only after I was done and we will see if I get any water. If not, i will run it again and then drain the block, but not the block and see what happens.
Maybe it was the mani to riser gasket, although there was no signs of a leak. With draining the block one time and the manis another, maybe I can narrow down where the water is coming from. Hopefully, maybe it is fixed, time will tell.
Any advice, and or recommendations are welcome!
 
I have not looked at the intake itself. I would think that if the intake was leaking, it would leak into the valley and there would be oil in the water.
And the shutters are fine, i checked them and this problem happens when it is stored out of the water on the trailer after running on the muffs
 
no water in the oil at all ? If yes there is no water in the oil but water in the cylinders there's is in my opinion 4 ways that keeps happening.

1- head

2- mani / riser

3- crack in the block.

4- someone rebuilt this motor and used the wrong cam / crank.

That's it end of story !
 
Hi Guys-
A little update-
today, i tried to start the motor after it had been sitting, block drained, mani's/ risers full for about 3 weeks, and again had water in #4 cyl. the rest dry. I also covered the carb w/ plastic to prevent the possibility of water getting in that way. I took off the riser and there was a slight trace of water streaking in the exhaust side, however no rust/ standing water in #4 like last time. The last time,. I replaced the riser to mani gasket and used perfect seal as recommended by a mechanic.
I am stumped!! anyone else having/ had the same problem?? I reallt do not think that it is the block, head, head gasket, etc.
thanks
 
Per Docksidemarineservices
...Get a piece of plywood and drill some holes in it to match the riser. Put a piece of rubber on it and bolt it over the riser port on the manifold. Pump the manifold full of air, about 10 lbs. Fill the exhaust ports full of water and look for bubbles...
Click to expand...
If you try what they suggest above you'll find the leak--a porosity issue w/cheap manifolds and risers. The Flinstones had better casting technology than the mfgr. of the mans. & risers you have. You pay for what you get.
 
Thanks for your reply.
I did try what was suggested. If you look at the post on 7-12-11, it will explain everything I did.
I am still stumped
 
Swap the exhaust manifolds and risers to see if the water issue follows. It is a lot of work but easier than pulling the heads. If it does then the problem is the manifold and/or riser. If it stays then it's the intake or head.
 
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