heater problem

[jwoo]

I have replaced my thermostat twice in a year and now my heater isn't blowing hot air and my temp gauge stays in the blue forever and suddenly (usually while sitting at a long light or drive through) it will go to normal but still the air isn't hot just luke warm. happens when it's 40 degrees or today 20 degrees. when it's 50 and above it works ok. Do I need another thermostat? Or does anyone have another idea what it could be? Or is replacing thermostats this often common in a 1995 ti ? Any feedback would be greatly appreciated.

[1996 328ti]

Moved to the proper section.
Lots to read but look at the sticky at the top of this section.