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Old 01-24-2015, 10:46 PM   #1
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Default Problem with leaking engine

Mercruiser 3.0 2004

Hi all,
Last summer I cleaned some rust off the block and por15'd it to protect it. Looks much better!
I found that the channel running from front to back was corroding. Turned out there was a hole in the underside of the raw water (saltwater) intake pipe caused by a raised section of corroded metal melting through.
I replaced that pipe and placed a silicone pad between the block and the pipe to protect it.
I winterized it today and have found that water is bubbling out of the top of the block. Only slightly at the moment and steamed off promptly which is how I found it.
What should I do to resolve it and is it critical? I hope not!
Please see images below.





On a happier note I also polished her today.....not bad for getting on 11years this year!



Cheers, Lee
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Old 01-25-2015, 01:54 AM   #2
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So it's boating season where you are and no chance of the water freezing in the engine which can cause damage?

Looks like a 4 cylinder 3.0 , correct? Not sue but could it be a leaking gasket between head and intake?
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Old 01-25-2015, 08:46 AM   #3
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Hi Mike. Yes it's a 4cyl 3.0
Boating season ended in nov but I was late winterising this year. I believe it may have been leaking for some years as the corrosion in that channel hasn't happened overnight. It was only in the summer when cleaning and painting the block that I found the damaged pipe and the corroded rusty metal underneath.
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Old 01-25-2015, 12:59 PM   #4
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Lee, I have a 3.0 and the top of my engine looks similar to yours. I assumed the rust was result of operating in a maritime environment and don't consider it a big problem. I also painted my engine with POR 15, but used the regular coating vice engine enamel. It's starting to flake off so I will re-do in the spring, only the right way this time.
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Old 01-25-2015, 02:29 PM   #5
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Ok so the corrosion is on the lip of valve cover and top of head as there are no water jackets here I must agree with jrsick. The only other possibility is if there is a water jacket between he head an manifold that is leaking at the gasket.
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Old 01-25-2015, 03:14 PM   #6
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Thanks for the reply. That's good to know that section is prone to rust and its not just mine then. Thinking about it more today...it could be that the water was just condensation sitting on the top as I didn't see if it was dry after the engine had been warmed up for winterising.
I shall recheck in the spring when re commissioning. Dry fully then watch while running. Water is easy to spot with a torch!
The raised section to the left with oil filler cap is the rocker cover??....so it is unlikely to be leaking water from that anyway?
And I would also assume the cast iron of the block is thicker so corrosion wouldn't eat through from the outside like that?
How thick is the block wall out of interest. Random question but someone may know.

Cheers, Lee
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Old 01-25-2015, 09:59 PM   #7
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I looked in my merc manual and verified there are no water passages between the head and manifold. The manifold is a combined intake and exhaust so it has raw water in it. The water jacket outer wall is at most a 1/4 inch thick.

The oil fill cap is on the rocker (valve) cover, the corrosion is at the lip of the cover where it bolts to the head.

Torch! Oh you silly Brits you mean a flash lite, no open flames around the engine
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Old 01-27-2015, 07:58 AM   #8
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Thanks Mike. That's reassuring to know.
Ps: you had a spelling mistake....should be flash "light".

Maybe worth some form of epoxy filler on the top to smooth out the corroded section followed by another coating of por15? Any recommended fillers to use? Would a metal putty work? If it was smooth again that would stop the water sitting in the low spots and prevent further corrosion.
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Old 01-27-2015, 04:44 PM   #9
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No I used "lite" to go with you torch, just my humor. Not sure there is any why to do this with out removing the manifold so you can clean up the rust them paint before coating with por15.
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Old 01-27-2015, 06:46 PM   #10
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Cheers Mike. Same humor then as I was joking about the differences in spellings for the same word.
When does your boating season begin?

All the best, Lee
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