Tell tale not working

[Foxcrew6]

Need some help from the boat scientists,gotta 1989 Mercury 50hp 3 cyl that I just had a new impeller put in but before I put the muffs on it and everything worked very well UNTILL I got it on the lake will unloading and driving approx 1/2 mile 1/4 throttle the tell tale stopped peeing and overheat buzzer went off so I shut it off and got to dock well now when you start motor tell tale pees fine for about 3 minutes then stops completely and the water starts coming out exhaust port above cavitation plate start above prop and will run idling forever with out over heating so I've tryed blowing air down and up to make sure there's no blockage,and wondering what could be up and if there's a thermostat on this motor

 

[Foxcrew6]

No boat wizards want to tackle this, took boat out again today only went 1/2 mile round trip but tell tale is very erratic, not a steady stream at all speeds very wired its acting like a thermostat acting up but I still don't even know if this motor has a thermostat I downloaded a manual but still can't tell about thermostat

 

[flyingscott]

Was the old impeller taken out in all one piece or did it have missing fins.

 

[Foxcrew6]

Had missing fins,I think I recovered most of them out of the intake fins,I have shot air and water both ways

 

[Texasmark]

Sounds like your smoking gun because nothing else makes sense and the problem is not constant, it varies as would happen with pieces of impeller floating around.

 

[Foxcrew6]

I came up with a piece floating around somewhere but instead of tearing a motor down to maybe find (A BIG maybe) I've decided to start and run everyday due to I live on the lake and it's my pontoon not my everyday fishing boat,and see if it will clear itself out and it see to be doing a lot better already (dam rubber piece)