Flushing the coolant went well but is rather time consuming with the repeated draining, bringing up to temp, draining, etc.
As for changing out the impeller...since I started up with the engine with the through-hull closed -- (hmmm, that's odd...I don't hear that splashing sound...OH CRAP) -- I thought it wise to change the impeller even though it did put out a good flow of water after I opened the through hull.
I did as others have posted and removed the pump. The pics below are of the impeller I removed. To me it appears to be in good condition. I have no idea how long it's been in service.
Where do you guys buy your Yanmar parts? I went to the local "Yanmar dealer" and was underwhelmed by the response I got. They don't stock impellers, seemed indifferent to ordering parts for me. Any online options?
Thanks for the help.