A flat core of thin tubes and fins at the very front of the car. Hot coolant runs through the tubes while air passing between the fins carries its heat away — the engine's main way of shedding heat. Modern radiators are aluminium with plastic end tanks.
A temperature-sensitive valve between the engine and the radiator. A wax-filled capsule expands as it heats and pushes the valve open: shut on a cold engine so it warms up quickly, open once it is hot so coolant can reach the radiator. Stuck open means a slow warm-up and a weak heater; stuck shut means overheating.
An impeller that pushes coolant around the loop. On most combustion engines a belt or chain drives it, so it spins faster as the revs rise; many newer engines and every hybrid or EV use an electric pump that can run at exactly the speed needed, even with the engine off.
At speed the air rushing through the grille is plenty. In traffic an electric fan pulls air through the radiator instead, sitting inside a shroud that funnels it through the whole core rather than just the patch next to the blades. It switches on by itself when the coolant gets hot — which is why you can sometimes hear it after the engine is off.
Expansion tank and pressure cap
Coolant expands as it heats, so the loop needs somewhere to put the extra volume: the translucent expansion tank, with MIN and MAX marks. Its cap is a pressure valve that lets the system run above atmospheric pressure, raising the coolant's boiling point by roughly 20 °C. Never open it on a hot engine.
Usually about half water and half glycol-based antifreeze, with corrosion inhibitors mixed in. Water carries heat superbly; the glycol stops the mixture freezing in winter (down to around −35 °C) and raises its boiling point. The inhibitors protect aluminium and rubber parts and wear out with time, so coolant has to be replaced every few years.
Oil cooler and intercooler
Two smaller radiators with their own jobs. An oil cooler takes heat out of engine or gearbox oil, often through a compact plate exchanger fed with engine coolant. An intercooler cools the air a turbocharger has compressed and heated before it enters the engine, so the engine gets denser air and makes more power.
Coolant temperature sensor
A thermistor — a small element whose electrical resistance changes with temperature — screwed into a coolant passage. The engine computer reads it to enrich the mixture on a cold start, to switch the fan on and to drive the dashboard gauge and warning light. It is the eyes of the whole cooling system.
Electric pump and multi-way valve
Electric cars swap the belt-driven pump for small electric ones that run only when needed. A multi-way rotary valve — a switchyard for coolant — then joins or separates the battery, motor and cabin-heating loops on command, so the car can send heat where it is wanted rather than just throw it away.
Chiller and battery cold plate
A cold plate is a flat aluminium plate with coolant channels, laid under or between the battery cells to draw heat out of them — or put heat in during winter. A chiller is a compact heat exchanger where the air-conditioning refrigerant takes heat from that coolant, which is what keeps a pack cool during a fast charge on a hot day.