My guesses based on little information would be 1)Bad coolant temperature sensor 2) Bad/sticking fan relay or 3) a short somewhere
starts showing wire at 4:09 if you dont want to watch the whole video
My fan was always on, in Feb 2019, in Toronto area. Temps were about 30F or lower.
I've heard this as well
It’s true. I replaced the ac condenser when I replaced my radiator. About a week later when I recharged the system the fan stopped running all the time.
In my case wasn't my car but fan would in one case kick on high and stay on once the key was turned to position 2 engine off and the temp gauge spiked all the way to red but I've had one of them be at normal temp but the fan would run for about 5-10 minutes after the car was turned off. I checked to see if I felt it was the ECT cause as moosed said I dont think anyone wants to throws parts at their vehicles if it wont fix the problem. In both instances luckily it was clear the ECT was faulty. That's why when I hear this problem I would immediately think ECT or fan assemby (specifically the relay but Volvo doesn't sell them and I just dont like used parts unless the owner specifically wants me to use them and even then depending what it is I try to urge them away from it). You obviously don't want to think it can only be those two things but the temp sensor aftermarket like I said is cheap so I would start there if I didn't have any way to test or read info from the ECM. The fan would be a last resort honestly for me I know it is known that they go bad but to me if its between pay 15$ to blindly test something vs 400$ for a new fan (I know many would try getting a used good one. I wont) I'd rather try the sensor but I'd even try checking A/C pressure before I try the fan if I was suggested to try that since I'm comfortable doing it myself but some people aren't or don't have the equipment to. If you have a scanner try checking the engine coolant temp reading in the ECM data stream if you can read the voltage being read or the resistance of the ECT that would help (that was for moosed) In your case since you replaced the thermostat and ECT since I haven't come across the problem myself and cant first handily experience the condition dont want to comment but gut would say fan assembly but brain is telling me "test something you fool do it now". Which I just mean its hard to diagnose when other than a description theres not much to go on
