I have a 2004 RX8, I have noticed the symbol for coolant system ( looks like a little house ). I have checked the coolant and it is full, my question is where is the thermostat located at so that I could change it out. I doesnt come on and stay on but I would like to get it fixed.

 

RX7's had a coolant level sensor tied with a buzzer - this sensor could go bad / wire corroded etc... so it may not be the thermostat, but a single wire sensor looking for 'ground' in the coolant.
BTW, changing the coolant may fix it, not sure what happens to its conductivity when it gets way old, could be coating the sensor in insulative gunk.