CM570 Two new Thermostats stuck open

[Finland25]

Hi. I have a 2002 cm570 and inframed it recently. They put a new coolant thermostat in it. I went to my first trip and after 700 miles my working temp drops from 175 to 120. I came back to shop and they replaced it with a new one. Now I I'm in the same situation again. 700 miles was 175 degree and now its sitting around 120 with 45 degree outside temp. My question is would it be a bad quality parts or dealer or shop do something wrong? Quick serve showing me a 4336659 for replacement 180 degree. Is anybody have an experience with Thermostats on this engine? Thanks for replying in advance.