No water out of outdrive

[WellcraftSportsman23]

I have a Mercruiser 5.0 with a bravo on it. At beginning of the season, I started as usual and noticed that it took almost 20-20 seconds for water to begin being pulled up the out drive from the ear muffs. This seemed odd but once it got a prime all was good. I had to replace the Manifolds and the risers and did so with OEM Merc parts. I did take the seawater pump off to inspect but all looked good, so I reinstalled. Upon completion of work, fired engine up and ZERO water gets pulled through the system. I disconnected where the seawater pump enters the thermostat housing and turn over and water comes out. I have taken off the Thermostat housing and manually turned the circulating pump and water barely moves out the Therm housing hole in the intake. I was thinking that I may have put the hoses one the seawater pump backwards but since water came out at the Therm housing I am no totally confused. So son questions:
1. Does the seawater pick up hose from the out drive go on the top of the seawater pump of the bottom.
2. If they were reversed would I get water coming out of the hose where it enters the Thermostat.
3. Can the Circulating pump be bad?
4. Thermostat housing is pretty corroded but seems like water can pass through. Can that be it.

 

[dubs283]

1. top, bottom hose goes to t-stat housing
2. no
3. yes, but probably not part of your issue
4. yes, but probably not part of your issue

most likely what is happening is the sea water pump impeller has a set and is having a difficult time priming on the muffs (common for brass housing pumps if this is the style you have), in the water it won't struggle as much because the pump is mounted below the water line

if you went as far as taking the pump off to inspect you're best off just replacing the impeller

 

[Bt Doctur]

1 depends on engine rotation
2 not likely
3 not likely
4 no
15-20 seconds if everything was drained for the winter

 

[WellcraftSportsman23]

So I found this. Inside of the plastic housing gauged as well. Ordered new housing and impeller. Plus new therm housing.

 

[dubs283]

So I found this. Inside of the plastic housing gauged as well. Ordered new housing and impeller. Plus new therm housing.

rough

fyi, plastic housing will have indicators as to "in" and "out" hose connections. all mercruiser oem sterndrive engines are standard (LH) rotation