Water overflowin in to expansion reservoir(overflow)

Over heating circulation problems. After driving the
car for a while. Water/ coolant overflows to
expansion tank. Have to keep drainin it and refilling
reservoir to radiator. Replaced water pump,
tensioner,crankshaft and drive belts,radiator,
thermostat .138000 plus miles.needs a tuneup.
Have to.top.it off as the temp guage goes past the
half/normal mark but it cools.down even
sometimes in idle.not sure if t stat are defective
upon purchace. Béen told possibly slightly blown
head gasket by a mechanik that worked on the
water pump and timing.checked oil it has sum
yellowish spots but most of.the oil.is just
well......oil. Just wonderin if maybe heater core
stopped up...Again. Any advice on what i can do to
resolve this till i can just simply get another vehicle
thats more dependable..Money is.tight!2006 Pt Cry