Troubleshooting mercury 90 water pump

[weatherman522]

Hi, I am trying to figure out if my water pump is working or not. Background: I had my boat out on the water and ran the motor at idol for about 10 to 15 minutes to charge the batteries with no issues. After shutting it down and fishing for an hour or so using the trolling motor I could not get the motor to start and had to be towed back to dock.
Now that I have it at home, I got the motor running but the water bleeder was not ejecting any water, I had the lower sitting in a large bucket of water. I had the inlets fully immersed but no water was being picked up (only the inlets were covered with water, not the whole lower assembly see picture). I decided to hook up the hose with the standard adapter and within seconds of turning the motor over the bleeder started ejecting the water.
Question: Is this typical behavior for these outboards to require some level of pressure, I would expect the water pump to pull/push the water through the motor with out any external water pressure, or is this a tell tell sign of the water pump not working? Is there some overflow hole that I am not covering to create the seal?
Any advice would be greatly appreciated, I am hoping to get this out on the water next week but don't want to risk the motor if the water pump needs replacement.

 

[GA_Boater]

If you only covered the inlets, the lower wasn't deep enough. The pump is above the inlets and and the pump has to be submerged to to pump. The pumps cannot work if not below the water level.

When was the impeller last changed? If it's been more than 2 years, change it for peace of mind and every 2 years.

 

[weatherman522]

Ok, that was what I was thinking. Does the propeller have something to do with the function of the pump? I appreciate the advice on replacing it, the previous owner told me he replaced is a few years ago and based on its condition I was considering replacing it anyways. Which is better for this type of motor/boat 3 or 4 blade props? I was planning on a 4 blade because I was told it would produce more thrust.

 

[Chris1956]

The propeller has nothing to do with the waterpump impeller. Replace the impeller, wearplate and 2 gaskets, as a minimum. Ask about which prop to buy in the prop forum.

 

[weatherman522]

Propeller, impeller... that's embarrassing, ha ha ha. thanks for the help.