Had too many issues last year to worry about the cooling system. My port motor would occasionally overheat and puke out coolant. Delving into that issue now. Engine seems like it's running great at this point.

Last fall I winterized both motors, and unscrewed the endcaps on the heat exchanger. Heat exchanger looked good, not clogged. No impeller pieces stuck in it, or anything like that. Couple tiny pieces of seaweed, no big deal.
I de-winterized the motor yesterday, unhooked the raw water pump, and ran the motor with end caps off, using the engine mounted circ pump only. I wanted to see if the heat exchanger was cracked or leaking anti-freeze into the raw water side. All good there, no leaks.

The only issue that I noticed, was the zinc on this side seems like it kind of fused itself to the heat exchanger. It's not clogging any passage, but when I remove the zinc plug, it's all blocked up. I can't get my finger in there. Should I use a drill or screw driver and open up that hole again, or wait until corrosion eats the anode and let it fix itself? The zinc on the starboard motor seems like it's completely gone. If I run aluminum zincs elsewhere, should this anode be aluminum as well? And, anyone know where to get an aluminum anode for the heat exchanger? All I see is zinc. (FWIW, I'm currently running zinc everywhere, but I plan on switching after my aft anode is done.)

At this point I'm guessing that air in my system was/is my biggest issue. I'm going to pull the hoses that are supposed to run coolant in them, and back fill them, to get as much air out as possible. The only bleed in the entire system that I see, is the small 1/2" nut at the very top of the heat exchanger. I don't see any bleed on the block whatsoever. Hopefully a new impeller and air bleed will straighten me out.