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  1. #1
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    Default How many hours can a raw cooled engine block last - mercruiser 3.0 liter

    I have 390 hours on my 10 year old mercruiser 3.0 liter that is raw water cooled and used in salt water. How many hours approx. can the block last? I take the boat out after every use and flush with salt away. I'm just in the process of replacing the exhaust manifold and riser now but I am concerned about the block.

  2. #2
    Vice Admiral tpenfield's Avatar
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    Default Re: How many hours can a raw cooled engine block last - mercruiser 3.0 liter

    I have 504 hours on my 21 year old Mercruiser 7.4 L always in salt water, never flushed, yada, yada, yada.

    It is as much a matter of age as it is hours.

    I'm gonna guess that at about 800-900 hours (8-10 more years), I will want a new long block
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  3. #3
    Moderator Bondo's Avatar
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    Default Re: How many hours can a raw cooled engine block last - mercruiser 3.0 liter

    Quote Originally Posted by Tmakaro View Post
    I have 390 hours on my 10 year old mercruiser 3.0 liter that is raw water cooled and used in salt water. How many hours approx. can the block last? I take the boat out after every use and flush with salt away. I'm just in the process of replacing the exhaust manifold and riser now but I am concerned about the block.
    Ayuh,.... Welcome Aboard,... Generally speakin', they last til the 1st winter it ain't drained...

    Then they Freeze Crack...
    Any Grease is Better,..... Than No Grease at All.......

  4. #4
    Chief Petty Officer mark1905's Avatar
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    Default Re: How many hours can a raw cooled engine block last - mercruiser 3.0 liter

    Quote Originally Posted by Bond-o View Post
    Ayuh,.... Welcome Aboard,... Generally speakin', they last til the 1st winter it ain't drained...

    Then they Freeze Crack...
    Not necessarily. 3.0s are notorious for having thin cooling passages in the block and corroding through eventually. I just got done replacing my 15 year old motor after having exactly this happen and getting raw water firehosed into my oil pan. Always a FL boat.. never frozen.

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  5. #5
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    Default Re: How many hours can a raw cooled engine block last - mercruiser 3.0 liter

    Quote Originally Posted by Bond-o View Post
    Ayuh,.... Welcome Aboard,... Generally speakin', they last til the 1st winter it ain't drained...

    Then they Freeze Crack...
    Lol. I do winterize.

  6. #6
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    Default Re: How many hours can a raw cooled engine block last - mercruiser 3.0 liter

    Ug, well I think I have a blown head gasket. I took the boat out today to test out the new exhaust manifold and reved it to 4000 rpm. WOT is 4400. Anyways the oil pressure and temperature were perfect but checking later I noticed that water got into the oil in the valve cover and puked out the top into the flame arrester. I checked the oil in the block and it was fine.

    I also noticed some antifreeze leaked onto the block in an area that has no hoses so I have no idea were that leak is coming from.

    Do I mead to replace the engine now???

  7. #7
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    Default Re: How many hours can a raw cooled engine block last - mercruiser 3.0 liter

    What brand is the "new" manifold & riser? Who's gaskets did you use?

  8. #8
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    Default Re: How many hours can a raw cooled engine block last - mercruiser 3.0 liter

    Quote Originally Posted by Pete104 View Post
    What brand is the "new" manifold & riser? Who's gaskets did you use?
    It's all oem stuff I bought.

  9. #9
    Senior Chief Petty Officer 04fxdwgi's Avatar
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    Default Re: How many hours can a raw cooled engine block last - mercruiser 3.0 liter

    Quote Originally Posted by Tmakaro View Post
    I have 390 hours on my 10 year old mercruiser 3.0 liter that is raw water cooled and used in salt water. How many hours approx. can the block last? I take the boat out after every use and flush with salt away. I'm just in the process of replacing the exhaust manifold and riser now but I am concerned about the block.

    1280 hours on my raw water cooled '92 7.4 L Mercruiser (and it came from Florida last year). Started yesterday for 1st time this season and she still purrs like a kitten.

    BTW, some years ago, I had a raw water cooled 3.0 Merc up in MA, used exclusively in salt water. Had over 1000 hours on it and she was just fine. Just flush it after every use, not allowing salt water to just sit in the engine / manifolds / risers.
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  10. #10
    Moderator Bondo's Avatar
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    Default Re: How many hours can a raw cooled engine block last - mercruiser 3.0 liter

    Quote Originally Posted by Tmakaro View Post
    Ug, well I think I have a blown head gasket. I took the boat out today to test out the new exhaust manifold and reved it to 4000 rpm. WOT is 4400. Anyways the oil pressure and temperature were perfect but checking later I noticed that water got into the oil in the valve cover and puked out the top into the flame arrester. I checked the oil in the block and it was fine.

    I also noticed some antifreeze leaked onto the block in an area that has no hoses so I have no idea were that leak is coming from.

    Do I mead to replace the engine now???
    Nope,... The antifreeze musta been from it's winterization, as there ain't any antifreeze in the runnin' motor....

    I'd think the water is condensation, if it ain't showin' up in the base...
    Any Grease is Better,..... Than No Grease at All.......

  11. #11
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    Default Re: How many hours can a raw cooled engine block last - mercruiser 3.0 liter

    Quote Originally Posted by Bond-o View Post
    Nope,... The antifreeze musta been from it's winterization, as there ain't any antifreeze in the runnin' motor....

    I'd think the water is condensation, if it ain't showin' up in the base...
    Sorry, I forgot to mention I added a FWC kit. Also the water/oil puked up through the valve cover breather into the flame arrester and down into the bilge.

  12. #12
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    Default Re: How many hours can a raw cooled engine block last - mercruiser 3.0 liter

    Quote Originally Posted by Tmakaro View Post
    Sorry, I forgot to mention I added a FWC kit. Also the water/oil puked up through the valve cover breather into the flame arrester and down into the bilge.
    I think I found the AF leak and I did another 4000 rpm test and this time there was no problems. The AF leak was a hose.

  13. #13
    Lieutenant Commander fat fanny's Avatar
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    Default Re: How many hours can a raw cooled engine block last - mercruiser 3.0 liter

    Are you doing this so called test @4 grand on muffs and not under load and in neutral? if you are your asking for trouble! I seen a guy do that last year @ the launch and it did'nt end wel.l
    1996 Searay 175 Five Series
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  14. #14
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    Default Re: How many hours can a raw cooled engine block last - mercruiser 3.0 liter

    Quote Originally Posted by fat fanny View Post
    Are you doing this so called test @4 grand on muffs and not under load and in neutral? if you are your asking for trouble! I seen a guy do that last year @ the launch and it did'nt end wel.l
    I did the last test like that but was nervious so it was only a few seconds. I guess that's a no no. It was the first And only time I have ever done that.

  15. #15
    Petty Officer 1st Class IES99's Avatar
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    Default Re: How many hours can a raw cooled engine block last - mercruiser 3.0 liter

    Quote Originally Posted by Tmakaro View Post
    I have 390 hours on my 10 year old mercruiser 3.0 liter that is raw water cooled and used in salt water. How many hours approx. can the block last? I take the boat out after every use and flush with salt away. I'm just in the process of replacing the exhaust manifold and riser now but I am concerned about the block.
    The blocks are pretty good and last a long time. The problems I've had with my 3.0 over the 24 years of ownership (all in salt water) is having the head corrode through so cooling water could enter (twice). Neither time did this ruin the block or the internals. That happened despite religious flushing and maintenance/changing of manifold, riser. Fe+H2O=rust. Salt is a very good catalyst for the reaction.

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