I just did the thermostat and the manifold it mounts to a few weeks ago on my Wife's 2010 Aveo5 LT. The drain for the radiator is on the bottom driver's side of her car. It takes a 13mm, I did it in a rush so it could be 12mm, wrench or socket but it was tight because of the condenser lines. I had the car up on ramps and got to it from underneath, there's a lot in the way to get to it from top down. The coolant drains out through the center of the mount that sits in a rubber bushing, so just put a bucket under that hole and you are good. The engine, radiator and hoses don't hold a lot of fluid, I ended up putting about a gallon back in.