The Fresh Water Flush – Do It Right, Or It Blows!

Hedda Woody Hopper Boater here. A little birdie has told me one of you out there broke the golden rule of flathead engine water flushing. You hooked up your hose directly to the water pump! Oh….

Now to some of you, you may be wondering what I am talking about. Well, for us here in brackish water we flush the engine a lot, for those of yous on fresh water lakes, you may use it to test an engine on dry land. Either way the issue is the same, and if you hook up the hose to your water pump, two things for sure will happen.


1. Head Gasket failure!

2. Water pump failure

And it happens fast. I am sure there is some sort of engineering term for this, but as the say’n goes. IT’S SUCK NOT BLOW!  What? You will remember it now won’t you. So how are you supposed to do it?

Phil and his 5 gallon bucket! Hey, it saved his boat as a bailer. WE ALL HAVE THEM NOW

One, get a 5 Gallon bucket. You need one anyway for other things.

Two, hook up your hose and run it to the bucket. NOT THE ENGINE

Three, Tie in a smaller hose to the area below your water pump. You will have to have a shut of valve. Easy hardware store stuff.

Four. Fill the bucket with hose water

Five, run the hose from the engine in into the bucket filled with water, keep the water running, the hose will SUCK the water into the engine.

Hose on engine TO…TO the bucket

That’s it, watch the pump SUCK the water out of the bucket. And you will have a happy ending. Yeah, walking a thin line here. But you will remember this now. Here is a short video of how it works.

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10 replies
  1. m-fine
    m-fine says:

    That is OK, but if I lived in salt or brackish water I would;

    1) move to a fresh water lake 😀


    2) put a fresh water cooling system in.

    I know no one makes a kit designed for the K, M and W flat heads, but the basic components are the same, you just need to figure out mounting and run some hoses. Jimmy should be able to handle it for you which makes the installation super easy. All you will need to do is take pictures and write a story or two. And write the check I guess.

  2. Greg Lewandowski
    Greg Lewandowski says:

    Yup, that’s how you do it. Even at idle, the hose water supply should not keep up with the flow the engine is using, and the bucket level should go down. If it does keep up, it’s time to install a new water pump impeller.
    You won’t have to worry about flushing in Port Huron. Engines love that bright blue water! See you in September!

  3. jim g
    jim g says:

    Or you crank the engine then turn the hose on. Then turn it off right before you turn the engine off. Simple.

  4. Johnny V.
    Johnny V. says:

    Or you can make the toilet plunger with a hose connection and prop it up under the water intake. Water will spurt out around the cup until the pump picks up.

  5. Troy in ANE
    Troy in ANE says:

    Jim G’s method also works well. Those of us on Well water also don’t usually have the pressure that city water has, so it is less troublesome.

    One other thing to keep in mind is that the water pump may need to be primed or you will overheat due to an air lock. I like to put my bucket up higher so there is a little “head pressure” to help start it flowing.

    (Image may be subject to copyrights)

  6. Mark
    Mark says:

    Attach the fake a lake to the thru hull as pictured. Attach a short hose with shutoff to that (off postion). Attach hose and turn water on. Start engine and then change shutoff to on position.

      GENE PORTER says:

      An even easier solution is to moor your woody in a marina on a tidal river where the water is fresh on the ebb. Then run the engine on the ebb – no hoses, buckets, fork lifts etc

  7. Bilgerat
    Bilgerat says:

    I use a 7 gallon “tote” container with my Graymarine 327 and it will empty in a minute if I’m running more than 1200 RPM, water hose can’t keep up. Fine at idle but I will be rigging up a new larger capacity water tank with bottom drain fitting for extended on land running sessions. I guess I’ll use the forklift to raise it up alongside the boat so the suction hose can do it’s job.

  8. Marty Feletto
    Marty Feletto says:

    Regarding running on a trailer, over the years I have used various “fake a lakes” which I make from toilet plungers. Some small, some large. I have not seen anyone mention the need to bring water to the cutlass bearing if you do not have a true neutral. I use a Y on the hose and separate “stand” to do this.

  9. Johnny V.
    Johnny V. says:

    I use a dish detergent/water mix to lube the cutless bearing for spring startup/winter layup-seems to work fine for the short period of time the engine is run.

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