@ GiraffeEars- I would like to add a couple of things. It may be best to change your cars thermostat when you are also doing a radiator flush. Since changing a thermostat already involves losing some coolant, there is no better time to do a full flush. You should also sand out the gasket sealant before inserting the new thermostat so you can get both the cover and base of the gasket housing. Your vehicle manufacturer often recommends doing both of these together every 48,000 to 60,000 miles. Good luck and have fun!