Likely bad ECT.

My guess is that you have more than 150K...

Best is to replace both the tstat + ECT.
I found a way to replace both w/o removing the PS Pump.

Here is a DIY for my 2006 XC90 2.5T.
You should check FCPEuro for PN for your year.
Stick to Wahler brand, about $100.

https://www ...

Hi everyone

I just recently started having this problem with my 2003 S60. After I turn off the car the radiator fan continues to run until the battery dies. The only way to stop it from continuing to run is by disconnecting it from the battery.

Trying to diagnose the problem more so I hopefully ...