I replied to you in one of your other threads about the heater:
http://www.toyota-supra.info/forums/...html#post78879
If you are getting heat part of the time the VSV I mentioned that may be intermittently failing, there may be air in the system, or the heater core may be thoroughly clogged and in need of a chemical back flush. Top off your coolant and try bypassing the valve I mentioned above as they're the easiest things to do.