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Impeller Priming Issue At Startup

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    #1

    Impeller Priming Issue At Startup

    I have a closed cooling system on my v-drive (raw water pumped into heat exchanger only). When I start the boat, no raw water is being pumped. If I idle too long, my engine will start to overheat. After the initial start-up, I have to go fast ~20 mph for the impeller to start pumping water. Once the impeller is primed, I don't have any trouble for the rest of the day. I can turn the boat off for awhile and start it back up and it will idle with no problems? Anyone know what could be causing this problem. Also, is this something I should be concerned that it could be causing damage elsewhere in the engine? I start the boat up and run it fast withing the first 5 minutes of it starting.

    Thanks!
    Tags: impeller, priming
    #2
    I'm curious about this, too, because I've seen photos of water strainers up high behind seats, and it seems to me the crank driven pump has to work pretty hard at first to draw water that high.

    No strainer in my boat, so I assume the water lines and pump are at or below water level and should be easy to pump/prime. Anyway, it's never been a problem on my boat.

    Do you have a water strainer up high?

    Thoughts?

    Comment

      #3
      I have a "high mounted" raw water strainer and my impeller pump has no problem drawing water through it immediately. Those impeller pumps have an impressive amount of suction - when they are working properly. Which makes me think yours isn't. Have you inspected the impeller for wear or damage? Or the pump housing for foreign objects? The performance of water pumps drops off FAST if something is wrong.

      I would open up the pump and check the impeller and the inside of the housing. If that all looks fine, work from there forward toward the raw water intake on the bottom of the boat, making certain everything along the way is OK. Anyplace the system could be sucking air instead of water, for example, could cause this behavior.

      Report back!

      Comment

        #4
        Don't forget to check where the raw water passes through the trans cooler (small cylinder in line in the water flow before the pump usually and has hoses connected to transmission). Those small passage ways will collect impeller bits if one grenaded before and other junk if you do not have a strainer. Even though my boat wasn't overheating, my transcooler was full of stuff from the previous owner.
        Mods: MLA BIG Ballast System (1800+ Custom sacs, 2 500 W705 sacs under bow), Duffy Surf Flap Mod, Trimmed Swim Deck, Top-Mount Starter

        Comment

          #5
          And as WA said, I installed the gasket wrong on my housing once and it was sucking air so it could not prime.
          Mods: MLA BIG Ballast System (1800+ Custom sacs, 2 500 W705 sacs under bow), Duffy Surf Flap Mod, Trimmed Swim Deck, Top-Mount Starter

          Comment

            #6
            ill have to check to see if I have a strainer (boat is on a lift at the lake). Are they typically high behind the rear seat?

            I'll also check the housing. I replaced the impeller at the beginning of the summer so there is a chance I didn't get the gasket on properly.

            Thanks for the suggestions.

            Comment

              #7
              Did you get the correct impeller? I have seen Jabsco and Johnson pumps on those engines. The pumps look similar but use a different impeller.

              Comment

                #8
                As mentioned by others these pumps can prime up to 2m of head or something. If there is an air leak anywhere it will struggle though . Much easier to pull air than water vertically!

                Sent from my HTC One_M8 using Tapatalk

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