I wasn't getting very good heat either. I replaced thermostat, cleaned-out the entire coolant system, replaced a couple of questionable hoses, all to no avail. What i ended up doing was pulling the heater core and cleaned it out in my basement washtub with a couple of chunks of garden hose- hot water inlet from the faucet, and one on the outlet drain back to the tub. With good doses of CLR, dishwasher powder, reversing the flow back and forth, and lots of shaking, thumping, and banging, all sorts of crud came out- sand, chunks of solidified reddish-brown coloured stuff, etc. Once the water pressure flowing out was the same as going in i knew it wasn't clogged anymore. She now blows pretty warm air, but not HOT by any means. Considering the amount of heat this engine puts out there should be thermo-nuclear heat blasting into the cabin, but i think this heater design kinda fell short. My two cents worth, anyway.
