COOLANT LEAK?????

Check the hose that comes from the radiator cap area and goes to the expansion tank

I just worked on a simular problem. I finally tracked it down. Someone added green anti freeze to dex cool and caused a sticky mess. I had to do a chemical flush on the cooling system, change the radiater cap, the thermostat and make sure the neck on the over bottle neck is not full of sticky gunk. Whats happening is the sticky anti freeze got in the radiator cap and couldn't stop the anti freeze from coming out the overflow. The engine was also overheating. Look in the overflow bottle and look for and feel for sticky or lumpy stuff.