Engine overheating

Hello.
Since I bought my car, I have a problem overheating engine. The water temperature needle is always at 1 graduation of the max.
To fix the problem, I changed the thermostat to a new one (180 °) but it didn't change anything. So I tried with a 160 ° but same result. (Overheating)
I decided to delete it and now the engine does not overheat. The needle stays in the middle, very often below. I can leave it as well but I know it's not good for the engine as it seldom reaches its normal operating temperature.
Do you know where the problem comes from?