I don't get it. The blendair door moves through it's full travel. When set on "cold", I basically get outside air temp through the vents, as I should. Set it to "hot", and I get temps of about 69-72*F through the vents in a garage thats 50*.

The engine DID have a bad T-stat causing it to peak at about 140*. I changed that and now the engine runs at about 185*, but the heat is still poor. When the engine is 185ish, the temp of the inlet pipe to the heater core is about 130*. The outlet pipe temp (w/the fan on high) is about 70* (same temp I'm getting from the vents), which would suggest that I'm shedding a lot of heat -and the heater SHOULD blow hot air. But it doesn't.

I don't get what's going on, other than I wonder if something is restricting water flow to the heater core. (?)

I don't get it.

 

Given the temps you are seeing, I think it is more likely that your heater core is seriously restricted, causing very little flow thru it, so the outlet temps are low.... Backflush the heater core, and see what comes out.....