Re: Johnson outboard repair guide
I received your PM, but if you post your question in the thread there will be more eyes to input their ideas.
If you are unsure of the age of the water pump, I would drop the lower unit and replace it. It is not difficult, yet much easier with a manual, especially your first time. I would also change the t stats as it sounds as if 1 is stuck shut by the description you provided in the PM. While it is out, flush the cooling system with the garden hose or compressed air from the water line at the lower unit to the t stat housing, then backflush from the t stat housing to the water line. Also ensure the water intake area is free of debris. If your alarm was not sounding, I would also look into testing that. This video may help as well. Good luck.
http://www.meegsonline.com/tmd/waterpump.wmv