Impeller turns but doesn't pump water?

[Wiggy]

My little 1983 Mercury 4hp gnat motor doesn't seem to want to pump water. The impeller turns as it should when the driveshaft rotates, but just will not pump water. I've even tried driving the driveshaft with a drill so that I can see if it pumps, but it doesn't

Any ideas?

 

[Bob_VT]

Re: Impeller turns but doesn't pump water?

The fins can be worn. The pump must be fully in water and also if you wand to turn it with a drill (it better be a strong one) you will need to go over 700 rpms.

Check that the impellar itself is turning and the keyway is in place.

 

[akwalker]

Re: Impeller turns but doesn't pump water?

Also,check that the hub isn't seperated from the rubber.

 

[Wiggy]

Re: Impeller turns but doesn't pump water?

The impeller is fine and is locked onto the driveshaft with the key. I've used this method on other lower units, and it's worked!

When I've installed the lower unit onto the outboard, it doesn't pump any water.

 

[Bob_VT]

Re: Impeller turns but doesn't pump water?

Is the water tube cracked? Maybe it is not connected at the top where it enters the block. I have seen that type of failure also.

 

[Wiggy]

Re: Impeller turns but doesn't pump water?

It's definately secured securely to something up there, so I take it, it's the block!

As regarding it being cracked, I've no idea, possible, but looks fine from what I can see of it.

I'll put everything back together again just in case I didn't get the water tube into the water pump last time, though I'm almost certain I did!

 

[Chopper Doc]

Re: Impeller turns but doesn't pump water?

The thermostat may be stuck closed too. And possibly you may have some leakage around the case haves causeing it to lose its prime. Just guessing, who knows. You may need to rtv everything and ensure it gets a good tight seal so it can lift the water without loosing prime.

Wes

 

[Texasmark]

Re: Impeller turns but doesn't pump water?

I agree on the fact that the pump must be submerged initially to get water to pump. I used to run engines in a barrel and when the barrel was full I had no problem but after I'd run the prop a few times and splash a considerable amount of water out the impeller would be above the water level and it wouldn't pump on the next startup.

Mark