thermostat

Hi, forewarning I have very little knowledge about cars so any help would be appreciated. I have a Corsa C 2004 1.2 in NHS blue that I have had a few problems with. First problem I had was with the radio as it doesn’t have a code and needs to get a chip rewritten or something to get it working...

So my issue is this and any advice will be appreciated. The car takes longer than usual to warm up, like 15-18 mins of driving and the coolant temp only reaches like 85°C. When driving it'll sit there until I come to a stop. Then after a few minutes of being stationary, it'll rise to 92-95ish...