Whatever is wrong must be pretty simple or basic. There are so few moving parts to this setup.

Got to spend a little time on this today:

- Checked coolant and it looks very clean, no crud.
- At engine start the water pump housing rose to 125F within 5-10 minutes, but both supply and return hoses from the water pump remained at 80F. I started wondering if I could have a blocked hose, or blocked nipple at the water pump - then I noticed there was a rattle sound from the water pump, so maybe an impeller problem?
- Took it for a drive and got it up to temperature: Forgot to try it in Defrost mode, but switching from Heat to Cold I got no change in air temperature.
- The blower motor works, and I get decent airflow out of the air outlet pointed at my feet.
- Back at the garage, I kept engine running at idle and measured 185-188F at the water pump housing. At the firewall, the driver's side hose measured 156F (inlet), the passenger side hose measured 114F(outlet) - so there must be flow thru the core. I forgot to notice if I still had the rattle sound from the water pump.

This seems like a functional core, but there is no harm flushing it, plus the hoses and nipples tomorrow. Maybe airflow thru the core is the problem, like the fins are clogged with lint or something, but that's internal to the airbox, so last ditch effort only.

I'll keep looking and fiddling with it.
- Art