Mercury 3.5 Outboard won't pump water

[sailcapt340]

A little out of sailing but, any ideas as to what is causing my Mercury 3.5 Outboard to not pump water. I've replaced the housing top (it was cracked), gaskets, impeller, grommets all the vital parts are new. The impeller turns with the shaft, the pin in centered in the impeller. The lines are clear (blew them out with air. It just won't pump water up to the head and out.
I get hot air out of water tube so it tells me everything is working except the water.
Thanks for any help you can offer

 

[Alan]

Are you sure you installed the impeller the right way, it wont work with the arms facing the wrong way. If it's OK I would take the lower unit to a water tank and spin the shaft by hand to see if water is passing through the pump. If it is you have a restriction in the water passage to or in the head. If not you will need to recheck the water pump assembly.

 

[Rich Stidger]

This might seem like a dumb question, but when the engine is running in gear (if you have a gear shift), does the prop turn?

The reason I ask is that it is possible to assemble the leg to the power-head with the shaft to the side and not in the splined crankshaft. Thus the engine will run but the prop and water pump will not be driven.

The hot air you sense coming out of the water tube output could be just hot expanding air within the power-head. I'm not sure that sense is a good indicator of an un-plugged cooling system.

 

[sailcapt340]

So far I tried all that you both have said

Alan And Rich,
I have tried the impeller in both directions, upside down and backwards. With no luck. I agree the shaft is hard to line up with the powerhead and sometimes it is guess work, but it is in and the prop spins.
I've checked with forced air in all the open ports and tubes and have no restrictions.
This one has really baffled me, but thank you for your kind help. I'll keep you posted as to my progress.

John

 

[sailcapt340]

Outboard if working again

Just as an update...
I have the water pumping once again. The problem was the metal spacer plate that goes between the bottom and top housing.
I placed it in with the opening port over the intake hole, thinking that the water had to come through there to get to the impeller.
The truth is it has to be blocked by the plate, which then causes the water to hit the plate, be forced through the chambers to the impeller and then up the discharge tube.
It took a while to figure this one out but was well worth the effort.
Thanks for the help guys, I hope this helps the next person.

 

[Rich Stidger]

Ah ha, the "old metal spacer plate with hole" mistake. Good T/S.

Since the impeller wasn't getting any water for cooling, I hope you checked the impeller for distress before re-assembly.

 

[Alan]

It was good of you to post the answer. So many times we go through the problem never to hear how it resolved, thanks.