1988 Johnson 4hp won't pump water

[blacksmith82]

Hi,

I have a 1988 Johnson 4hp (J4RCCS) that will not pump water. I have replaced the entire water pump assembly including the housing, plate, impeller, etc. This motor discharges water through holes in the leg. When I first replaced the assembly it pumped water through the holes in a steady stream for a few minutes, and then it just stopped. Since then I have gone through everything I can think of and I can't seem to get it to pump again. I removed the powerhead to see how the water flows and ensure there was nothing clogging it which there wasn't. I can feel some suction at the vents in the lower unit so it seems like the impeller is working. Does anyone have any experience with this motor or any ideas as to what could be causing this? Any advice will be much appreciated. I have spent quite a few hours on this one.

Thanks

 

[SolingSailor]

Re: 1988 Johnson 4hp won't pump water

The OEM service manual has a very good water flow diagram.
Most of the water exits just above the prop, under the water. The small holes relieve exhaust pressure at low idle, and serve as a water flow telltale. Normally, drops of water just spit out of the leg holes. If you are sure the pump is working, you then have to ensure that the water tube is properly inserted at top and bottom. Since you say it was working for a while, this is probably OK.
The water level must fully submerge the pump, so it must be several inches above the antiventilation plate. Another possibility is that a piece of the old impeller has broken off, and is attempting to travel through the engine. If so, you will have to remove the exhaust cover, head, and check the cooling passages. For this you will need the manual, if you don't have one already. P/N 507659

 

[Bosunsmate]

Re: 1988 Johnson 4hp won't pump water

Remove the gearbox. Attached a hose to the input pipe, turn on gently. See where the water comes out of. Start motor check water comes out ok still so that there isnt a pressurizing problem in the powerhead. If thats going ok, unless the water/ exhaust outlets a blocked in the gearbox it must be the pump.
The key may of not being put in quite correctly.
I agree with Sailor too, often people dont fill the tank high enough for the pump to work, it has to be a good few inches aboves the level of the pump impellor in the leg, and make sure its in neutral so the water isnt getting mixed around too much

 

[blacksmith82]

Re: 1988 Johnson 4hp won't pump water

Thank you for the advice. I have tested the pump with the lower unit off the motor, using a drill to rotate the dive shaft. Water shot up about 6 inches. I believe I am going to make a test water tube to insert and see how high the water will pump so I know if enough pressure is being created. When I run the motor now I am getting a small amount of water through the holes. Previously I removed the power head from the leg and tested the water tube and the vents through the powerhead and didn't find anything clogging them. Currently when I run the motor I am getting some drops of water "spitting" out of the holes in the leg; however, when I first replaced the impeller I had a strong stream coming out of these holes and that's what I am trying to get again.

 

[Bosunsmate]

Re: 1988 Johnson 4hp won't pump water

Put the hose on gently with a gentle flow onto the input pipe going up the leg while you have the gearbox off and RUN the motor too. If the hose blows off or water doesnt come out where it should you have a pressuring problem such as a leaking gasket under the powerhead or an internal pressuring problem.
If that seems ok you will probably have to have another look at the impellor.
You should also check that the driveshaft is turning all right and hasnt had its splines stripped.

 

[dockrat100]

Re: 1988 Johnson 4hp won't pump water

I have a similar motor to yours that I just got finished doing a total rebuild on the cooling system. I don't know why something would change in your motor, but I can tell you that mine kind of spits out of the hole you referred to, no steady stream, ever. Does the engine run hot? I guess I would be more concerned with the cooling system cooling than if I was getting a solid stream from the telltale holes.

 

[Bosunsmate]

Re: 1988 Johnson 4hp won't pump water

If you a checking the impellor, have a look that the key is all right as if it has cracked it may turn with the driveshaft at the beginning and then start slipping

 

[Bosunsmate]

Re: 1988 Johnson 4hp won't pump water

Hello Blacksmith, what happened with your endeavours?