Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
The first thing that you want to do is check the cooling system for any exhaust gases. There is a tester for that, that you can gt from Autozone for about $20. It comes with instructions, but there is a blue fluid that is used in it, if the fluid turns yellow, that is exhaust gases.
Block tester available as:
Napa BK.(NNN) NNN-NNNN/span>
OEM/Block Tester AUTOZONE
Part Number: 27145
If there are any exhaust gases in the cooling system, that will cause more pressure than desired and will allow the engine to burn coolant and/or heat the coolant up too high.It may be releasing the pressure after it's shut off.
If there are, then there would be an internal engine problem, like a head gasket or head.