I installed a soft spring t-stat a few months back and since that time my warm idle has ranged between 195-197. Yesterday, albeit a little warmer weather, i noticed my warm idel running at 204. I think I am still safely in the proper range I should be in, but am wondering what caused this sudden spike in idle temps. When driving the vehicle runs a solid 188 and sometimes dips down to 186.

Thanks in advance for the insight.

 

What brand thermostat did you use. Also check the radiator for cold spots.

 

Could also be a weak fan clutch.