Toyota Repair: 1993 previa overheating, radiator hose, temp guage

Question
My previa began overheating.  I flushed out the radiator twice.  Workeed for a while, then overheated again.  The temp gauage began jumping from moderate to very hot.  When I turned on the heater, it would lower the temp guage.  A friend suggested a new theromstat and possibly a water pump.  First, could that be the prblem, where is the theromstat, can I do it myself, and the same questions relative to the water pump.

Thanks a bunch.  Need to save money and try and fix it myself.

Answer
Try changing the thermostat and see if it helps, it is located underneath in the housing at the end of the lower radiator hose on the water pump, there are three 12mm bolts that you have to remove and the thermostat can be removed. If that doesn't help get back to me.