is this a blown head gasket ?

proper filling of the over flow botlle is a 50/50 mix of antifreeze and water and should only be 1/4 full or just barley covering drainhole in bottom of overflow tank. As engine gets hot overflow bottle will fill and it may puke a little. When it cools the coolant will draw back into the engine and appear empty when cool. I would still shoot for bad stat first, then go for cap. Most overheat problems can be tracked to a small leak. How is your heater core? I always end up having to rplace them on all my 60's Darts. Is there fog or a smokey like skum on the winsheild that you have to clean at least once a week? Sweet smell in when the heater is on. When you are running "Hot" does running the heater change anything? Please advise.