Hello and welcome, Super mechanic here. Thank you for trusting us with your concern. I will do my best to help you with your question.
Unfortunately, it sounds like you may have a blown head gasket and you’ll likely need to take it in to get it repaired or at least do the test yourself.
About your friend's 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. Most times not filling the crankcase with coolant either.
If there are, then there would be an internal engine problem, like a head gasket or head.
Of course, you will want to make sure that the system is full, the coolant is circulating,as well as the pressure cap holding pressure. Thanks