Yamaha 50hp not pumping Water

[Gasper Master]

Thanks for all of the help guys. I looked at my impeller again and I had knocked the key out when i put the impeller on. Luckily it fell into one of the small recessions on top of the lower unit. I put the key on and reinstalled the impeller. I also pulled my thermost and it looked fine. But, I put the cover back on w/o reinstalling it. I cranked the motor and she started pissing like a drunk man. I put the thermostat back in and she's still pissed.

I guess either the thermostat was stuck, or in the process, i flushed out something that was clogging her up??? I'm glad she's working, but I would sure liked to have put my finger on the problem. I think I'm going to go ahead and change the thermostat as a precaution since its a cheap part and so easy to change.