the heat only blows cold air at normal temp, unless i drive it down the road. i just changed the thermostat and its the 192 oem but before.. as soon as the gauge moved it started blowing hot air. what could be wrong? heater core?

 

If your heater starts blowing hot when you rev up your motor then cools back off when you let off and return to idle then more than likely you have a coolant leak allowing air into the system. That or your reservoir went dry and then the system got air in it. You should try doing a pressure test on your cooling system if you have access to a pressure pump.

 

Couple of questions:
Are you getting warm air only once the temp gauge comes up? (That is normal.)
Are you getting cold air, but warm air when you rev the motor? (That would indicate air in the system, a blocked line to the heater core or a failing water pump.)
Did you bleed the air out of the system when you changed the thermostat?