I'm going to assume you are commenting on the radiator no longer having a cap (IE radiator cap omission)
So, to clarify, the radiator cap (pressure cap) exists.....but it is located on the surge tank.
This design has been used on various cooling systems since the late 50's. (I point to Corvette in this case)
It also is used on my 1995 and 1996 Impala LT-1's.
Regardless, I continue to believe the surge tank operation is being confused with a coolant overflow tank, such as found on my 1996 Blazer.
Vehicles that use a overflow tank have the pressure cap mounted on the radiator and any expansion of coolant is directed through a hose to the tank.
When the vehicle cools after shutdown, the coolant is drawn back into the radiator through negative pressure.
The overflow design purpose is to keep the actual radiator full at all times, maximizing efficiency and, by having no air in the core section, the coolant won't gel.
The surge tank, as found on the Cruze in this discussion, is simply a remotely located place for coolant expansion to take place and, because it has air space, there is no overflow bottle required.
Therefore, as long as the level is above the hose inlet, at the bottom of the tank, when cold, it is considered 'full'
The airspace above the level is required so the cooling system pressure will remain below 20 psi.
This is the caps designed relief pressure.
If one was to fill the surge tank to its maximum 'HOT' level, and the coolant is not at 210 degrees (variable) the now very small airspace remaining will reach and likely exceed 20 psi before the engine is fully warmed up.
This will result in the cap releasing pressure, venting just ahead of the fresh air inlet and 'viola!'.....you now join the 'I smell coolant crowd'
I keep the coolant level 1/2" above the lower tank hose checking it first thing in the morning.
I have operated the vehicle with a pressure tester installed......results were surge tank pressure at that starting level never exceeded 14 psi......a nice sized buffer zone against cap venting.
My experience and $.02.........the 'FULL HOT' arrow means just that.......never exceed the tip of the arrow under any circumstance.