Never mind the image labels..
or you started out with gunky looking coolant and the heater core is
plugged enough with the gunk that even with what looks like good flow*,
it wont work.. or you might have both problems.
*If you think just a couple passages open wont look like good flow, pull
off your shower head or the aerator on your sink faucet.
* Bad water pump will result in the source hose to heater being hot, exit
hose from heater to WP being cold.
Yeh, I'm a Krusty old Geezer, putting up with my 'smartass' is the price
you pay..DEAL with it!
Click to see the full signature.