Mercruiser 3.0 Leaking Water On Top of Manifold

[MercruiserWestra]

Dear fellow boaters,

This past fall I recently acquired a boat equipped with a Mercruiser io 3.0 engine that initially had starting issues. After conducting a thorough examination, I discovered a bent intake valve and promptly had the valve seat reseated at a trusted machine shop. Following this, I replaced all necessary gaskets and rebuilt the carburetor to ensure optimal performance.

Initially, after reassembly, I successfully managed to start the engine and achieve smooth idling while using muffs in my garage. I never had a chance to get it out in the water before winterizing it as it was end of November.

However, as I prepared to take the boat out for a run after winterization today, a new issue emerged. Upon starting the engine and idling on muffs, I observed water seeping out of the plug hole on the back of the boat with fuel/oil. Upon closer inspection, I determined that the leak appears to be originating from the area near or above the gasket connecting the head to the exhaust/intake manifold. The water is running down the back of the engine and along the side, indicating a potentially serious issue. Could it be the manifold gasket? Could the pressure in the exhaust be pushing the water out to make it look like it is boiling? As seen in the video, could water be leaking past the threads of the head bolt?

To provide comprehensive context, I have attached detailed photos and videos for your review.

While considering potential causes such as improper sealing, damaged gaskets, uneven torque application, and the possibility of a cracked manifold, I am reaching out to this community for further guidance. Despite my efforts, I have been unable to pinpoint the exact source of the leak and resolve it effectively before I take it all completely apart.

In light of this, I would greatly appreciate any insights, suggestions, or troubleshooting tips that could help me identify and rectify this persistent water leak issue. Your collective expertise and advice would be invaluable in getting my boat back on the water and running smoothly.

Thank you sincerely for your time and assistance.

 

[Bondo]

Could it be the manifold gasket? Could the pressure in the exhaust be pushing the water out to make it look like it is boiling? As seen in the video, could water be leaking past the threads of the head bolt?

Ayuh,..... Welcome Aboard,..... Can't be the intake manifold gasket, No water behind it,....
Head bolt is possible, I use a teflon paste on mine, were yer's sealed at all,..??

Is that hose right there leaking,..??
The t-stat housing,..?? or it's hoses,..??

 

[Scott Danforth]

How did you winterize?

 

[bbook83]

There is a drain plug on the underside of the manifold. Is it coming from there?

 

[Scott06]

There is a drain plug on the underside of the manifold. Is it coming from there?

Yeah that looks like under the manifold drain.

 

[MercruiserWestra]

Ayuh,..... Welcome Aboard,..... Can't be the intake manifold gasket, No water behind it,....
Head bolt is possible, I use a teflon paste on mine, were yer's sealed at all,..??

Is that hose right there leaking,..??
The t-stat housing,..?? or it's hoses,..??

I used permatex high temp thread sealer on the bolts. The hose is not leaking or any of the hoses.

 

[MercruiserWestra]

How did you winterize?

1)Put stabilizer in gas
2) Run the engine and spray fogging oil into carb and kill it.
3) After it has cooled take drain plug out of the manifold and block
4) Once drained put plugs back in and take hose clamps off of tstat
5) pour antifreeze down the hose until comes out tstat and pour it into the exhaust hose and the intake hose.
6) Open drains again for a little bit and replug it
7) change oil and oil filter
8) change oil in outdrive
9) take out batteries

 

[MercruiserWestra]

Yeah that looks like under the manifold drain.

No, sadly it is running along the back corner of manifold and then onto the wall and dripping down the plug.

 

[Scott Danforth]

1)Put stabilizer in gas
2) Run the engine and spray fogging oil into carb and kill it.
3) After it has cooled take drain plug out of the manifold and block
4) Once drained put plugs back in and take hose clamps off of tstat
5) pour antifreeze down the hose until comes out tstat and pour it into the exhaust hose and the intake hose.
6) Open drains again for a little bit and replug it
7) change oil and oil filter
8) change oil in outdrive
9) take out batteries

did you probe the drains in #3

 

[dubs283]

With the engine running on muffs use a mirror and light to inspect under the intake/exhaust manifold near the area where the head mounts to the block and you might locate the source of the leak

 

[Lou C]

Yep probing the drains is very important.