Read this:
"why is a car's cooling system under high pressure? Simply, to increase the boiling point of the coolant. This does two things. 1) it prevents localized boiling in the system which helps avoid overheating. Second, it increases the operating temperature of the coolant. This allows the engine to run hotter which is generally more efficient. Additionally, by having the coolant hotter for a given ambient, the cooling system is more effective, since heat transfer is a function of coolant".
And it is a closed system, there will be pressure in the system.
Now check few things:
u have recently installed the radiator. check if there is no air remains in the system.
does it overflows the coolant when hot from the bottle or the cap
hows is the temperature needle. does it goes to hot or not.
Water level stays same or u need to put water every time u drive.
