 If it's got the proper amount of coolant in it, the radiator cap or the pressure cap, depending on what type of system, they call it different things, but either way, the cap on that is supposed to keep the pressure limited at a certain area. Typically, it's gonna be, let's say, around 14, 16 pounds, some of them 18, 19, 21, but it keeps pressure in there, but it also is meant for vacuum so that when it gets above that level,