Toyota Repair: 95 toyota exten/cab 4 cyl pickup, head gasket problem, heater coil

Question
My engine starts to overheat when I turn the heater on. If I turn the heater off it will cool back down. I have new t-stat,radiator and hoses. Heater coil has been cleaned out.?  Any chance it is a head gasket problem ? I'm going nuts with this...and it's cold too !

Answer
Yes there is a good chance that the headgasket may be the problem, there is a simple test that can be made, most repair shops or the toyota dealer can do this, it involves using special equipment, one is a checmical test that involes using a blue test fluid in a container attached to the radiator opening, some vapors are then drawn into the test tube and if the fluid changes from blue to green or yellow then there is an internal combustion leak, the other test is more accurate, it involves using an emission analizer, both methods search for hydrocarbons in the radiator vapors.