1975 9.9 johnson doesn't pump water as you open throttle up.

[littlelakeden]

Hi everyone.I have a problem.I just bought this motor.It is a 1975 9.9 Johnson. When it idles it pumps water fine I think.When I start to open it up the water slowly stops flowing out the back.At wide open the water stops completly.I changed the impeller and still the same thing.The water is very hot coming out at low speeds.I was wondering if this has happened to anybody else or if you might know how to fix it.I was thinking the thermostat might be shot or plugged up with god only knows what.Any knowledge would be greatly appreciated.

 

[Daviet]

Re: 1975 9.9 johnson doesn't pump water as you open throttle up.

Could be a head gasket leaking into the cooling system, the higher the RPM the more compression goes into the cooling system. The pressure from the cylinders over comes the water pump pressure.
Might try taking a compression test.

 

[littlelakeden]

Re: 1975 9.9 johnson doesn't pump water as you open throttle up.

I will try that tomorrow.Thanks.

 

[Beek14]

Re: 1975 9.9 johnson doesn't pump water as you open throttle up.

Did you replace the whole water pump? Or just the impeller. A lot of times the plate or housing can have grooves worn into them causing it to not have correct pressure to continuously push water through the system.

 

[littlelakeden]

Re: 1975 9.9 johnson doesn't pump water as you open throttle up.

i replaced just the impeller.i will look at that as well.thanks.