I have a 2001 s60 2.4T and just recently replaced the ECT sensor and thermostat. A couple hundred miles after doing so my temperature gauge has been acting up. Mainly it has been going all the way to the hot side and I've been getting the "High Engine Temp" message that also says "Stop Car Safely ASAP". I am assuming that my thermostat may not be operating properly. I got it from ipdusa.com.

Can anyone give me suggestions on this issue and am I correct in my diagnosis?

 

If the coolant level is good and you can't feel the difference in heat radiating from under the hood, verify temp with a thermocouple on your digital volt meter or by using an infrared thermometer or find someone who does.
By verifying the temp, you'll know if it's the sensor or the t-stat.
Ed