is it possible to have some leftover coolant in motor after headgasket change

 

yes, you should change the oil after doing the gasket job. there is usually a very small amount of coolant left after a gasket change and oil change but it should evaporate with first run to operating temp. if you have doubts and its possible that coolant is still leaking then better get the coolant system pressure tester out and test it.

 

You must change oil after a head gasket replacement. DO NOT drive a car with coolant in the oil, it will cost you a motor.