no thermostat
 

Since the weather is warm, I wanted to flush my coolant and change the thermostat. Got a mazda oem thermostat, but when I went to remove the old thermostat, there was no thermostat. I bin running all winter with no thermostat. Anybody know if any damage would of been done with running the car without a thermostat?

Potentially there is the issues of hot spots that were not cooled properly (fluid moved too fast through the system to transfer the heat).

If your temps never rose, no damage probably. Your car probably took forever to warm up though huh? Running without a thermostat can cause overheating, since the coolant is constantly moving too fast to allow it to absorb much heat. Even race cars run a restrictor plate of some sort to slow down the coolant flow. I say you should be ok, just put the new one in.

you may have damaged your internal water jacks. As there is no thermostat, the water will be flowing really quickly, i am suprised the radiator hasnt started leaking.