Coolant system issue?
 

I'm having an issue with my 91 civic dx 1.5L.

My Dad just had the head resurfaced, put a new head gasket, radiator, timing belt, water pump, thermostat, radiator cap. All was good after the above work was done until about 1 & 1/2 months later.=-then it started transferring coolant between the overflow reservoir and the rad and back again. After driving it, the overflow is about an inch or so over the max fill line, after sitting for a while the radiator seems to suck most of the fluid back until the reservoir is barely over the fill line. This happens everytime I drive it, now. It isn't overheating, per the temp gauge, anyway. I also can't see any antifreeze on the ground or anywhere under the hood, though. In 2 months since the job was done now, the rad only needed to be topped off once, about a 1/2 cup.

Anyone have any ideas what to have checked or do next? What could be the cause? I appreciate any help.

Sounds like the coolant system is working correctly. (xferring coolant back and forth to the coolant reservoir is normal)

Best practice:
-fill coolant reservoir to min level
-purge all the air out of the coolant system (run the engine with the radiator cap off; allow engine to come up to operating temp; use the little coolant bleeder nut on the top radiator hose connection near the engine block to burp any trapped air)
-top off radiator
-fill the coolant reservoir to the halfway point between min and max
-put the radiator cap back in place
(monitor coolant level by looking at coolant reservoir and add coolant to the reservoir when low)