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Mercruiser 470 pressure test

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  • Mercruiser 470 pressure test

    Hello guys iam trying to find out why a/f is getting in my oil I took the exhuast manifold off .caped off the front hose coming from the head hooked up pressure tester to the hose coming from the intake manifold pressure tested and it holds 15 psi Aim I safe to say that my engine I.e head gasket cam seals are fine thanks for the replies

  • #2
    Re: Mercruiser 470 pressure test

    Bad cam seals might not show up on a pressure test. AF would get into the crankcase under some pretty specific conditions. The engine would need to be running which would pressurize the coolant, BOTH seals would have to be bad AND the water pump weep hold would need to be plugged, which would result in coolant leaking past both seals under pressure into the crankcase. If the weep hole is clear, coolant leaking past the first seal would dribble out of the weep hole rather than be forced past the second seal into the crankcase. So make sure the weep hole is clear (toothpick or wire inserted into the hole) and if it is clear and no coolant leaks out when the engine is running your cam seals are OK.
    Terry
    87, 4WINNS H 190
    470/Alpha I

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    • #3
      Re: Mercruiser 470 pressure test

      Originally posted by stonyloam View Post
      Bad cam seals might not show up on a pressure test. AF would get into the crankcase under some pretty specific conditions. The engine would need to be running which would pressurize the coolant, BOTH seals would have to be bad AND the water pump weep hold would need to be plugged, which would result in coolant leaking past both seals under pressure into the crankcase. If the weep hole is clear, coolant leaking past the first seal would dribble out of the weep hole rather than be forced past the second seal into the crankcase. So make sure the weep hole is clear (toothpick or wire inserted into the hole) and if it is clear and no coolant leaks out when the engine is running your cam seals are OK.
      thanks for the reply i ran a large paper clip in the weep hole with the pressure pumped up to 13 psi and saw no a/f coming out. do you think i need to try this and turn the engine over a few times. also i could only get the paper clip in about 2 inches does that sound right thanks again for your help.

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      • #4
        Re: Mercruiser 470 pressure test

        Sounds like the weep hole is clear (sometimes folks see the coolant leaking out and plug the hole to "stop the leak"), and with no coolant leaking looks like that is not your source of coolant in the oil. The only other sources that I can think of are the exhaust elbow or the head gasket. Of those two seems like the head gasket would be most likely. Good luck.
        Terry
        87, 4WINNS H 190
        470/Alpha I

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        • #5
          Re: Mercruiser 470 pressure test

          stony if the head gasket was bad would i be able to hold pressure at 15 psi ?

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          • #6
            Re: Mercruiser 470 pressure test

            Doesn't seem like it should, but there are just not that many ways for coolant gt get in the oil. Head, exhaust or maybe a cracked head or block. Could be only leaking when up to temperature and the coolant pressure builds.
            Terry
            87, 4WINNS H 190
            470/Alpha I

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            • #7
              Re: Mercruiser 470 pressure test

              Hey, in regards to the weep hole. You will need to push something flexible(small zip tie) into the hole. A flexible wire will work also. The weep hole has a small curve in it. About 3 1/2 inches is how long the weep hole is. Some weep holes will stop up from grease that was used during the installation of the seals. Sometimes it takes a few times of ramming the grease with said item to clear the hole. The weep hole is between the seals, so no worry of tie or wire damaging the seals.

              "GET'EM OFF THE BOTTOM"

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              • #8
                Re: Mercruiser 470 pressure test

                Originally posted by stonyloam View Post
                Doesn't seem like it should, but there are just not that many ways for coolant gt get in the oil. Head, exhaust or maybe a cracked head or block. Could be only leaking when up to temperature and the coolant pressure builds.
                hi stony
                I know that i do have a leak in my exhaust manifold between the gasket and riser iam working on fixing that i replace the gasket and still leaks so that is why i was thinking if the engine holds pressure that it will eliminate head gasket or any other problem. i am having a problem with sealing the riser even with a new gasket i still lose pressure. the reason i asked about pressure testing the engine was if the riser gasket is leaking would it dump alot of a/f into the oil. some people said i would lose but it should be going out the exhaust not in the oil also the engine runs perfect just when i get back to the dock oil is higher and a/f is low thanks again for all you help

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                • #9
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                  Re: Mercruiser 470 pressure test

                  thanks for the reply i tried a paper clip but could only get it in about 2 inches ever time i pulled it back out there was grease on the paper clip i will try again thanks for you help

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