ng_randolph
Bjorn H
No need to drain the coolant. Remove the reservoir cap briefly to relieve pressure before replacing the thermoswitch. Remove the old thermoswitch and and cover the opening with the ball of your hand while you fiddle with getting the new one positioned. You'll lose a bit of coolant, and you'll have to bleed a radiator after you're done.I would assume you can't remove the thermostatic switch unless you remove the coolant first?
If the old thermoswitch is broken, by all means replace it. I would not replace a working switch with one rated at a lower temperature. It will not provide any material benefit, but it will make your fans run more often.