There are a few things you can do but cooling systems, especially since you don't know the car are challenging. In my experience 90% of overheating problems are NOT related to the thermostat. You should be running at 190-205 not more. Get yourself an infrared thermometer and verify the temp, hit the gage in a couple of different spots, lower radiator hose, upper, water pump etc. and note the readings. If lower and upper radiator hose temp fluctuates, it is your radiator. Check the water pump for flow, check to make sure you have enough coolant, if you have A/C make sure your fan clutch/fan works. Get yourself a manual to read up on how to check all these things if you don't know.