When driving for about 15 minutes or so I start to smell coolant and noticed The overflow bottle is completely filled up and leaking out the vent hole on the top. When it cools down the level in the bottle never drops back down.

This is what I have done so far
Flushed out cooling system
Replaced radiator cap
Replace thermostat
Cleaned Radiator

I can hear the fan running when the key is turnd on and engine is off when the engine is hot.

The only thing I can think of is air is getting in somewhere. When I have the time i’m going to fill the cylinder up with air and see if it’s leaking into the cooling system.