90 HP Mariner leaking water

[Twinminnow]

I recently bought a 90 HP Mariner. The previous owner told me that it is appr. 7 years old and "has a water leak on the upper portion of the motor." He said he had been told that it might be a warped head or a bad head gasket. After insuring that I had an ample water supply to the motor, I started it to find that it runs "fairly well" but also confirmed the leak. While not "spraying," there is a slow discharge of water coming from the threads of the upper spark plug. The lower 2 cylinders don't appear to exhibit that symptom.

A local Marina owner told me that the motor does NOT have a head gasket. ?? The only other tech that I could find in the area suggested that the spark plug on that cylinder might be loose. Am I "brain-dead" in thinking that there should be zero water entering the combustion chamber of any cylinder, thereby tossing out the theory of a loose spark plug allowing the water to escape? (The latter tech also suggested the possiblity of it being a warped head/gasket problem.)

While I'm quite comfortable in working on "land-based" 2 & 4 stroke engines, this "marine critter" is a new challenge for me. Any thoughts or suggestions would be appreciated!

 

[corm]

Re: 90 HP Mariner leaking water

Hi,

Your water jacket gasket is leaking. A simple fix.
I'm surprised the dealer did not know what the trouble was.
Unless you were talking to a clerk or something.
As for the tech well..........

 

[Twinminnow]

Re: 90 HP Mariner leaking water

CORM,

Thanks much for the info! Will try tomorrow to find/order the offending cover gasket with hopes of also obtaining torque specs. for the cover bolts.

 

[emckelvy]

Re: 90 HP Mariner leaking water

Here's a good site for parts diagrams for your motor, they're listed by HP then Serial # so be sure to jot yours down:

http://www.mercruiserparts.com/SelectModelType3.asp?class_id=2

Torque for cyl block cover bolts is typically around 70 inch-lbs, but I can't recall the size of the 90-3's bolts. In the absence of a manual, use SAE standard torque specs for the actual size of the bolts (which, BTW, are most likely metric).

http://www.machinetoolhelp.com/Repairing/bolt-torque-chart.html

http://www.raskcycle.com/techtip/webdoc14.html

http://dodgeram.org/tech/specs/bolts/M_bolts.html

Note, if this motor is a Salty Dog, those bolts are likely to be stuck. Use a careful application of heat from a MAPP or propane torch to help bust them loose. If you break them off, you'll be drilling & tapping, that's no fun!!!

If you find that they're really not wanting to come out, a Quick and Dirty fix would be to pull the spark plug of the offending cylinder, degrease thoroughly (including spark plug body), reinstall spark plug, and seal around the hole with automotive-grade RTV. The Hi-Temp red or regular Black will do a good job.

This of course is a temporary fix and you'd have to re-do it anytime the spark plug was removed. But if you need to get out on the water it'll work for the time being.

Don't use sealants of any kind containing copper as this can create a corrosion cell with the aluminum, when subjected to seawater.

HTH.........ed