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351 Water in Oil Question?

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  • 351 Water in Oil Question?

    I found the aft right freeze plug pushed out into my bilge one day last winter after a hard freeze. I replaced the freeze plug back in May, then ran the engine for about 20 minutes. Afterwards the oil had turned milky.
    I'm just getting around to trying to find the source of the milky oil. I pulled the exhaust risers, manifolds, intake, and heads tonight.
    I'm going to take a more thorough look at things tomorrow, but the only thing I saw that may have caused the milky oil was the head gasket on the back right cylinder was damage around the top of the cylinder. The ring in the head gasket had split there.
    Is it possible that this is the only damage I have?
    I need to take a wire wheel and get the remaining gasket material off the mating surfaces of the manifolds, intake, etc, to get a better look, but initially everything looks ok.
    Anywhere else I should check before putting things back together?
    Is there anything in the lower block that can crack and allow water to get into the oil?
    Thanks!

  • #2
    I assume the one you pushed out was on the starboard rear. It seems to be the most common one in 351s that gets pushed out. There are water jackets in the block that can crack and lead to your troubles.
    Tim
    Gone, surfing.

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    • #3
      I just ran across this, awhile browsing around this morning. Looks like a good deal, hope you don't need it, but hard freeze and Welch plug pushed out says you just might.http://gainesville.craigslist.org/boa/4614878303.html

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      • #4
        Nice price or a turnkey replacement -if it's what it says it is.
        sigpic...A bad day water skiing still beats a good day at work...1995 Pro Star 205....

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        • #5
          Originally posted by CantRepeat View Post
          I assume the one you pushed out was on the starboard rear. It seems to be the most common one in 351s that gets pushed out. There are water jackets in the block that can crack and lead to your troubles.
          How do you determine if a water jacket in the lower block is cracked? Right now I have it torn down to the short block. Going further would probably require pulling the engine. Is that the only way?

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          • #6
            Well, that's kind of a problem. The crack maybe big enough to see with the naked eye or could be so small that you can't see it. It might be a hairline crack that only leaks water when it's hot and under pressure.

            IIRC, there is a post here where someone is having the same issue as you. His crack seemed to be in the lifter valley. It was at the center inside water jacket and had a previous repair attempt done on it. You might look there first.
            Tim
            Gone, surfing.

            Comment


            • #7
              Since you mentioned a problem in the valley, one thing I found that might be my problem is a hole in the valley behind the forward wall, aft of where the distributor drops into the block. That paper towel in the picture is in the distributor hole.
              I know this hole isn't supposed to be there. Not sure if water could get in there, or how freezing could cause this.
              Could this be my problem?
              Attached Files

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              • #8
                What I have done in the past is use brake clean and wash down all of the visible areas of the block where you suspect a crack. Just spray really well, don't scrub. Then watch it as it dries and if there is a crack, it will stay wet longer than the rest and become visible. Quick alternative to a dye check. Don't forget to do the cylinder walls as well. Just don't forget that if you don't find a crack this way, it doesn't mean there is not one.

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                • #9
                  That hole is from the casting mold, nothing to worry about, it does not lead to a water jacket. A hole that size would have water running out of your valve covers in just a few moments of running.

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                  • #10
                    Originally posted by whiskeyriver View Post
                    What I have done in the past is use brake clean and wash down all of the visible areas of the block where you suspect a crack. Just spray really well, don't scrub. Then watch it as it dries and if there is a crack, it will stay wet longer than the rest and become visible. Quick alternative to a dye check. Don't forget to do the cylinder walls as well. Just don't forget that if you don't find a crack this way, it doesn't mean there is not one.
                    I don't see any evidence of a crack. I guess I could hit everything. I did find one of the head gaskets on the aft right cylinder with the cylinder ring in the gasket split. I was wondering if that my cause it?

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                    • #11
                      Originally posted by tockit View Post
                      I don't see any evidence of a crack. I guess I could hit everything. I did find one of the head gaskets on the aft right cylinder with the cylinder ring in the gasket split. I was wondering if that my cause it?
                      a crack in the head gasket could let water in.
                      sigpic...A bad day water skiing still beats a good day at work...1995 Pro Star 205....

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                      • #12
                        Post a pic of the head gasket. Also the top of the piston in that cylinder.Yes it can cause water in the oil. However if the water was entering through the cylinder, you should have noticed the engine skipping/running rough. Especially at start up after sitting. Also there are areas of the block around the cylinders and water jackets that cannot be seen without pulling the engine and completely disassembling. And sometimes not visible to the naked eye even then. The only way to be certain is complete disassembly and have a machine shop pressure check the block. I suggested the brake clean trick because if you find a crack that way it saves you the trip to the machine shop. The only other option I see is put it back together with new gaskets and run it keeping a close eye on the oil. Not what I would reccomend though.

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                        • #13
                          Here's a picture of the head gasket. Not a very good one.
                          Attached Files

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                          • #14
                            That head gasket looks like its been blown and not a freeze issue. Do you have a photo of the piston and cylinder head from that side? Is the piston really clean with no carbon on it?

                            Also, where that ring is broken is right next to a water jacket. You might get away with having the heads surfaced and new gaskets.
                            Last edited by CantRepeat; 08-19-2014, 07:04 PM.
                            Tim
                            Gone, surfing.

                            Comment


                            • #15
                              Originally posted by CantRepeat View Post
                              That head gasket looks like its been blown and not a freeze issue. Do you have a photo of the piston and cylinder head from that side? Is the piston really clean with no carbon on it?

                              Also, where that ring is broken is right next to a water jacket. You might get away with having the heads surfaced and new gaskets.
                              I don't have a picture of the piston and cylinder head, but it doesn't really look that much different than the others. I cleaned everything up and looked at all the mating surfaces around the water jackets and I still don't see anything.
                              I'm at a loss. Where are the most common places these things crack at when they freeze?

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