Need help - 3.0 with water in cyls. 3 & 4

Pritchard

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Joined
Jun 16, 2009
Messages
5
Hi, I'm new here and new to owning a boat. I bought this boat only a week ago.

This boat has a 1991 Merc 3.0L that was running great when I bought it last week. First trip out on water, 45 minutes running, then loss of some power and rough running. Brought home and discovered water in cyls. 3 & 4. Pulled head and had it resurfaced. Took .008 tho get it flat again. Paperwork that came with the boat shows head being rebuilt just 15 months ago. When disassembling engine, I found that the last two bolts through intake/exhaust manifold were missing. This might explain where the water came from.

I put it all back together today using a new gasket set and following proper procedures. Compression is low, 65 psi, on all 4 cyls. I think maybe pressure tester is bad. Crank the engine and cyl. 3 is not firing. Readjusted the valves and tried it again. Same thing but running a little rougher. Pulled all plugs and spun the engine over. Water shot out of both cyls. 3 & 4. Needless to say, I was very upset. I'm back to square one.

Any thought on what may be causing water to get in the cyls? I am fairly competent when it comes to getting an engine to run, but I'm no expert on marine engines. Any and all help is appreciated.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,468
Ayuh,.... Welcome Aboard,..... My 1st guess is the manifold/ riser gasket has failed, droppin' water into the back cylinders,.....

Sounds like the valves are too tight, or the compression tester is Junk,....
 

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,093
the manifold to riser joint or the riser has a hole in it or the manifold is cracked or the shop missed the hole under the exaust valve
 

Pritchard

Recruit
Joined
Jun 16, 2009
Messages
5
Thanks for the replies.

Manifold riser? Is that the same as the exhaust elbow? If so, the gasket was new, but there could be some physical damage. I did not notice anything cracked or broken. It cleaned up well and appeared to be intact. I'll take another look at the valve adjustments. I might have them too tight.

What/where is the hole under the exhaust valve? Are you referring to the drain plug in the manifold?
 

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,093
on an old head the cast iron is eroded away and a hole developes under the exaust valve
 

fishrdan

Admiral
Joined
Jan 25, 2008
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6,989
Agree with others, check the manifold and riser, and mating surfaces between the two, to be sure they are sealing.

If you pull the manifold, remove the riser, block up the manifold to where it's sitting level, fill it with acetone and watch for internal leaks int eh intake and exhaust passages. (Acetone will leak through cracks water will not.) I had the same thing you are describing, cracked manifold that was filling cylinder 3 and 4.... The manifold was cracked in #2 exhaust, but running back into 3-4
 

s.hadley81

Petty Officer 1st Class
Joined
Jun 22, 2011
Messages
245
I had a similar issue recently with water in the cylinders and I meticulously maintain my boat and as everyone that has responded said I would definitely check the riser I had a riser gasket blow out on me and the gasket was new last season also do you know if the boat was ran in saltwater or freshwater it sounds to me you need to look at your manifold and riser on a boat they a maintenance item(basically disposable) of course running in saltwater they wear out faster
 
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Pritchard

Recruit
Joined
Jun 16, 2009
Messages
5
Thanks for the replies. I got so frustrated and angry, that I took it to a local marine service center for diagnosis.
 
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