leaking heater pump causing overheating?

[996scott]

This past weekend we spent the morning boating with no issues. Later when the engine was in neutral and we were filling the ballast I got a ECT Higher Than Expected and my engine temp was over 200. I checked the coolant level and it was fine. I shut it off and did some reading here online. I read where if I got up to speed/rpms up the temp would come down and sure enough it dropped to 165 in a matter of 20 seconds as long as I had the rpms up. When i stopped and was just in neutral the temp would start climbing. I called it a day, come home and put the boat away. I read that the heater pump was a common problem and would leak out coolant. I checked the coolant tank and it was completely empty. I pulled the heater pump off and there is definitely dried purple on the bottom of the pump. So I'm guessing that the leaking heater pump was the cause of the high engine temp? We did have the heater running for several hrs so that all makes sense that the coolant was slowly leaking out but why would the coolant tank be full if that was happening? And then why would the tank be empty after sitting for a few days?

Can I replace the pump with any pump or is this made for coolant and not water? I'm assuming any pump will do.