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#4434499 - 06/17/17 06:14 PM 1989 Merc 9.9 water entering lower cylinder
Bluestream Offline


Registered: 09/13/03
Posts: 5758
Loc: Waterloo, ON
I have a 89 Merc 9.9 That runs rough at idle and higher speeds. Lower plug always looks wet/grey emulsion and often small water droplets on.

Compression good at 105 PSI in both, gas is fresh and 50:1
New plugs installed, both getting good spark. (has aftermarket CDI box)
Carb (has carb from an 8HP) was taken apart and was spotless. Fuel needle/seat held pressure for 10 min, float set to 1 inch
Reeds appeared to be good and sealed tight
Float was good and main jet clean
Low speed jet at 11/4 turns out

I have replaced the exhaust cover gaskets and they looked fine, but still same issue. (I could see water in lower with cover off)
Is there any way for water from cooling system to enter the cylinder? I have heard lower seal can let water in, any truth to that?
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2000 VW Beetle 1.8T M5
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#4434581 - 06/17/17 07:50 PM Re: 1989 Merc 9.9 water entering lower cylinder [Re: Bluestream]
Donald Offline


Registered: 03/21/04
Posts: 20469
Loc: Upstate NY
It's been awhile since I have fooled with an outboard. What about the head and head gasket?
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#4434686 - 06/17/17 10:20 PM Re: 1989 Merc 9.9 water entering lower cylinder [Re: Bluestream]
Bluestream Offline


Registered: 09/13/03
Posts: 5758
Loc: Waterloo, ON
These merc's have no head. Cylinder/head is all one piece, but if they had a head, the gasket would be the first place to look
_________________________
2000 VW Beetle 1.8T M5
2000 Ford Explorer 4.0 4X4
1991 BMW 735iL
"A fool and his money are soon parted" - Thomas Tusser

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#4435088 - 06/18/17 12:11 PM Re: 1989 Merc 9.9 water entering lower cylinder [Re: Bluestream]
JTK Offline


Registered: 08/14/03
Posts: 10590
Loc: Buffalo, NY
Seems like a leak in the cylinder jug between the water jacket and cylinder somewhere, but like you say, the compression tests OK. It would have to be a minuscule leak that only crops up under certain conditions. Ugh..
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#4435137 - 06/18/17 01:00 PM Re: 1989 Merc 9.9 water entering lower cylinder [Re: Bluestream]
dwendt44 Offline


Registered: 05/17/06
Posts: 3971
Loc: Central Wisconsin
The exhaust covers could be a place that might have a leak.
The cover over the exhaust could be rotted or cracked, the water jacket
cover over that cover would supply the water.

Though I'm more familiar with larger O.B. engines.

My 2
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#4435162 - 06/18/17 01:29 PM Re: 1989 Merc 9.9 water entering lower cylinder [Re: Bluestream]
Bluestream Offline


Registered: 09/13/03
Posts: 5758
Loc: Waterloo, ON
I have replaced the exhaust cover gaskets as mentioned in 1st post. The covers and the inside were pristine as a fresh water engine.

First image shows the gray water oil mix by lower exhaust ports





Edited by Bluestream (06/18/17 01:33 PM)
_________________________
2000 VW Beetle 1.8T M5
2000 Ford Explorer 4.0 4X4
1991 BMW 735iL
"A fool and his money are soon parted" - Thomas Tusser

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#4435583 - 06/19/17 12:01 AM Re: 1989 Merc 9.9 water entering lower cylinder [Re: Bluestream]
dwendt44 Offline


Registered: 05/17/06
Posts: 3971
Loc: Central Wisconsin
Use a straight edge to make sure that both plates are flat.
If the tattle-tale and the exhaust path are clear, there should be no
back pressure on the cooling flow.
_________________________
There's no such thing as:
Too big of a battery,
Too large of a gas tank,
or too loud of a horn,
or too bright headlights.

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#4435699 - 06/19/17 08:31 AM Re: 1989 Merc 9.9 water entering lower cylinder [Re: Bluestream]
Bluestream Offline


Registered: 09/13/03
Posts: 5758
Loc: Waterloo, ON
Thats good advice, I will check them for trueness. I assumed that because they were so thin the clamping force of the bolts would pull the cover in tight even if they were a bit off.

Other sites have suggested the lower crank seal may be bad, but I cant see how that would matter, as that area is not exposed to any water.
_________________________
2000 VW Beetle 1.8T M5
2000 Ford Explorer 4.0 4X4
1991 BMW 735iL
"A fool and his money are soon parted" - Thomas Tusser

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#4435878 - 06/19/17 11:59 AM Re: 1989 Merc 9.9 water entering lower cylinder [Re: Bluestream]
dwendt44 Offline


Registered: 05/17/06
Posts: 3971
Loc: Central Wisconsin
Quote:
Other sites have suggested the lower crank seal may be bad, but I cant see how that would matter, as that area is not exposed to any water.


True. The water has to come from the block itself, it's not under much pressure
and it should flow right back out normally. If the propeller is open and the lower
unit hasn't been worked on prior to the problem, I'd check the water outlets all the
way down to the prop.

My 2
_________________________
There's no such thing as:
Too big of a battery,
Too large of a gas tank,
or too loud of a horn,
or too bright headlights.

Top
#4436148 - 06/19/17 06:49 PM Re: 1989 Merc 9.9 water entering lower cylinder [Re: Bluestream]
Donald Offline


Registered: 03/21/04
Posts: 20469
Loc: Upstate NY
Maybe better done in January, but stop in to a Merc dealer and pick his brain. He should give you some advice if you hint you will buy the needed parts from him.
_________________________
2015 Subaru Forester 2.5 engine/CVT
2015 Ford F250 w/Powerstroke
2016 Subaru Crosstrek CVT (wife's)


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#4438912 - 06/22/17 08:06 PM Re: 1989 Merc 9.9 water entering lower cylinder [Re: Bluestream]
Bluestream Offline


Registered: 09/13/03
Posts: 5758
Loc: Waterloo, ON
Yeah, I've been to the dealer a few times. Parts guy only offers so much info, or only knows so much. Said 99% of the time its exhaust cover gaskets. I have re-seal the gaskets with loctite 518. I will pressure test the cooling system to see if the block is cracked. Not sure what else to do....
_________________________
2000 VW Beetle 1.8T M5
2000 Ford Explorer 4.0 4X4
1991 BMW 735iL
"A fool and his money are soon parted" - Thomas Tusser

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