My 1993 sc300 will occasionally heat up ...after driving on highway with gauge at halfway mark... when I come to a stop or slow down ... when the rpm's are low .... the gauge begins to creep up...if i put in park and increase rpm it will cool down ... replaced radiator, water pump, clutch fan, all water hoses and thermostat.... any suggestions....

The heater core, which is located in the dashboard of your car, is really a small lexus radiator (http://catalog.overnightradiator.com/lexus-radiator.html). The heater fan blows air through the heater core and into the passenger compartment of your car. The heater core draws its hot coolant from the cylinder head and returns it to the pump -- so the heater works regardless of whether the thermostat is open or closed..how about taking it for a mechanical check..