All the coolant from my rad keeps emptying into the overflow. Every day almost I have to fill up the rad but the next day this coolant ends up in the overflow tank. I have replaced the thermostat and rad cap but it still has the same problem. I have noticed that right after running the engine, the coolant in the overflow is bubbling. I tried flushing the coolant and bleeding it but still same problem. I don't know what else I can do. It's not overheating but the lower rad hose seems to take a really long time to get hot so I'm thinking maybe the new thermostat isn't working properly? What else could cause the coolant to keep emptying into the overflow but not come back?