How to replace the thermostat on a 2001 Volvo s40?

Very easily done. The thermostat is located on the left front part of the engine connected to a hose coming from the radiator. It is held on by (2) torx head bolts. The plastic shroud above it will need to be removed first, but that too is very easy. After letting the engine cool down completely, remove the bolts and shift the thermostat housing cover out of the way. Take out the old thermostat with your fingers and replace with the new one. You should replace the gasket as well. The thermostat and gasket will set you back about $10 from any auto parts store. The entire process should take less than 30 minutes. Good luck.