2002 ford taurus coolant bubbling out of coolant tank cap?

Coolant is bubbling out of the tank cap on my taurus. The coolant is a bit over the fill to line. The coolant is the normal green color. I don't think it having a bit of extra coolant in the tank is doing this. The cap itself maybe? I just bought this car and it didn't do this until today.

Go to an auto parts store and puschase a chem test kit for the coolent. It will tell you iffin combustion gasses are entering the water jacket.
thing is, cross contamination of fluids (oil/coolent) is not a diffinative clue as to iffin a head gasket is bad or not. Combustion chamber gasses in the water jacket do not always exhibit signs of oil in water or water in oil. So…
possible thermostat issue otherwise.