Just replaced the thermostat on my '89 525i. Still no heat. What else besides a faulty thermostat might cause this? Brrrr!

Make sure you purge all of the air out of the system...BMWs are notorious for this if you didn't bleed it properly.

Did you turn the heat all the way up on the HVAC unit, too...this opens up the water valve and sends coolant into the heater core?