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Johnson raw water pump losing prime

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  • Johnson raw water pump losing prime

    Can someone give me a little insight on a Johnson raw water pump? Mine is mounted directly to the front of the crank shaft on my LT-1 and uses an 812 impeller.

    I believe the raw water pump is self priming, but I never noticed the problem I am having now with my previous 80 SS boat. My nagging issue is loss of water prime and circulation at engine start with idle speed. This failure of flow results in an excessive engine temp until a flow rate can be established at which point the engine temp immediately drops back to normal at 160, and will remain regardless of engine speed.

    BACKGROUND:
    1 Impeller and gasket replaced beginning of this season new. Removed in inspected today, found normal.
    2 All hoses (b4 and after pump) removed and back flushed for obstructions including trans cooler, strainer and pick up inlet on hull. No obstructions found.
    3 Removed outlet hose from water pump to 160 thermostat housing to check flow rate, appears strong once flow is established.
    4 New t stats 160 drilled and 140, installed proper direction and location. Both checked for proper operation on the stove, normal.
    5 steam tube mod performed 2 seasons ago.
    6 ALL hoses pulled and blown clear with compressed air or water, no obstructions found.
    7 no water leaks anywhere, all clamps tight, I don't find any place where it could be sucking air.
    8 water strainer is mounted horizontal level with hull immediately after thru hull pick up, not plugged and always full. Water line runs horizontal to hull directly from strainer thru cooler to pump.

    My "at the lake" solution, has been to pump the throttle while in neutral after start up to establish flow. Engine idle is normal, I believe around 600. I can tell immediately when flow is established because the raw water pump, manifold hoses and 140 housing become cool to the touch.

    I can idle all day, pull a footer, leave it idle, pull another skier, leave it idle and so on and the temp never moves more that +-5degs weather at idle or WOT. If I shut the engine off between sets though, it will heat soak a bit (normal) and then upon start up proceed to rise through 180 towards 210 if I let it at idle speed. Pump the throttle 2-3 times, flow begins again, raw water pump housing and hoses cool and block temp drops right back down and stays at normal. I have gone far enough as to pull the 160 t stat housing when the 180 over temp was present to see if it was open, it was.

    Bottom line that I can see is the Johnson raw water pump looses its prime at engine shut down and at start up idle speed isn't efficient enough to pull new prime. By cooling system design, there is a vent tube off the 160 thermostat housing leading to starboard riser so I know air can move both ways ie: pump tends to back drain. Removing pump cover does NOT yield any water draining. The only possible variables I see now are removing strainer (shouldn't be culprit) or replacing pump. Pump appears normal, doesn't leak and I chased this issue last year which is why impeller is new and strainer was added.

    Has anyone else been down a similar path, what are your suggestions, all appreciated.

  • #2
    Was the boat used in salt water? The pump also wears and loses priming capability, the wear increases especially in salt water and with some sand mixed. Affraid it's time for a new pump!

    Sent from my GT-I9505 using Tapatalk

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    • #3
      I bet it's your strainer. Get a piece of 1.25 OD PVC pipe and put that in place of your strainer to test.
      -Tim

      Making boomers great again!! Boomin'

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      • #4
        If its not the strainer, it may be the shaft seal on the backside of the raw water pump.
        Sometimes they leak water out, sometimes they leak air in.

        I rebuilt my raw water pump. You just need a seal & copper washer from indmar/johnson pump/skidim and two commonly available bearings.
        Bailey
        '02 X-9
        Lake Blue Ridge

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        • #5
          Fresh water use only and I don't think the strainer is the culprit since I had issue prior to strainer install. I was considering the rebuild, but thought the housing may be the problem and figure to just chomp at a new pump. Guess a $30 rebuild can't hurt though as a try before buy $270 pump. Thanks

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          • #6
            Originally posted by CruisinGA View Post
            If its not the strainer, it may be the shaft seal on the backside of the raw water pump.
            Sometimes they leak water out, sometimes they leak air in.

            I rebuilt my raw water pump. You just need a seal & copper washer from indmar/johnson pump/skidim and two commonly available bearings.
            RWP is a critical component - +1 on should be rebuilt or replaced after almost 20 years. I replaced mine with new this year. You don't want to see the second picture
            Attached Files
            sigpic...A bad day water skiing still beats a good day at work...1995 Pro Star 205....

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            • #7
              I had the same problem and I've just bought one new for $170. The rebuild kit only has bearings, seals, impeller and some have the lobe. On mine it was the casing that wear, so the rebuild kit was not an option.

              Sent from my GT-I9505 using Tapatalk

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              • #8
                where do you get a rebuild kit?

                I have a small water leak on mine....

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                • #9
                  bakesonline has the parts.
                  sigpic...A bad day water skiing still beats a good day at work...1995 Pro Star 205....

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                  • #10
                    If you look on ebay for 10-24805-01 you will have a lot of new pumps for sale. I bought from michiganmotors for $171.60 . If you pump is not priming at idle and it's npt leaking it's either because it needs a new impeller or a new housing

                    Sent from my GT-I9505 using Tapatalk

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