Q: How to replace the thermostat and water control valve in a Nissan Maxima's cooling system?A: First of all, before you replace the thermostat, inspect the coolant level, and temperature gauge. Detach the battery, drain coolant in your cooling system, and take off the old thermostat and install a new one. apply some sealant, let it cure, then refill and bleed the cooling system on your vehicle.