What a radiator actually does
A radiator is two tanks and a core of tubes and fins. Hot coolant walks through. Air takes the heat. The cap holds the pressure that keeps it from boiling.
Pull the slab off the nose and you can name the parts without a book. Two tanks. A honeycomb of thin fins between them. Pipes in and out. A neck with a cap on it. That is the radiator. It is not the fan. It is not the plastic bottle on the inner fender.
Hot coolant leaves the engine and lands in one tank. The tank feeds a stack of flat tubes. Air walks through the fins that are brazed to those tubes and takes the heat with it. The far tank collects what is left and sends it back. Crossflow puts the tanks on the sides. Downflow puts them on the top and bottom. Same job. The thermostat is the door that decides whether this loop is even open. This core is the dump.
Pop the cap on a cool engine and you are looking down the neck into that first tank. Green or orange or pink — the mix. The hose on the side is how it arrived. People treat the translucent bottle as the radiator. That bottle is overflow, or a remote expansion tank. The chemistry still has to crawl through the fins.
The cap is a spring. Twist one apart and you get a coil, a rubber seat, and a valve. The spring holds a few pounds on the system so the mix can sit hotter than a kettle without boiling. When pressure beats the spring, a little coolant lifts into the bottle. When it cools, vacuum pulls it back. The number stamped on the cap is that spring, not a suggestion. Crack it hot and you just dumped the pressure. The mix can flash.
The thin slab in front of the core is often the A/C condenser. Same fins. Different loop. A fan pulls air when you are sitting still. Clogged fins or a stuck thermostat will cook you either way. People flush the radiator. The door never opened. The radiator is the dump. The cap is the lid that lets it run hot.