Radiator

The radiator is the primary heat exchanger in the engine cooling system, responsible for transferring the heat absorbed by the coolant from the engine into the airstream passing through the vehicle's front grille. It consists of a core made up of hundreds of thin aluminium tubes running between two tanks (one on each side or top and bottom), with corrugated aluminium fins bonded between the tubes to maximise the surface area exposed to airflow. Hot coolant from the engine enters the inlet tank, flows through all the core tubes simultaneously, and exits through the outlet tank as cooled coolant returning to the water pump. The flowing air between the fins carries the transferred heat away. Modern radiators are aluminium-core, aluminium-tank or aluminium-core, plastic-tank construction — the latter being more common and lower cost, though more susceptible to cracking at the crimped joint between the core and plastic tank. Radiator capacity ranges from approximately 6 litres on small cars to over 12 litres on larger vehicles. Crossflow radiators (coolant flows horizontally) are the dominant modern design; downflow radiators (vertical coolant flow) are found on older vehicles and some trucks.

The radiator must dissipate enough heat to keep the engine within its operating temperature range of approximately 85–95°C under all conditions, including sustained high-load operation in high ambient temperatures. The heat transfer rate is determined by the temperature difference between the coolant and the ambient air (a larger temperature difference transfers more heat), the surface area of the core (more fins and tubes transfers more heat), and the airflow velocity through the core. At highway speed, natural airflow provides substantial cooling capacity. At idle or in slow traffic, the electric cooling fan supplements or replaces natural airflow to maintain adequate cooling capacity at low speeds. The radiator's capacity must match or exceed the engine's maximum heat rejection rate — typically 40–50% of the fuel energy is released as waste heat. A radiator that is undersized, partially blocked, or externally contaminated reduces this heat rejection capacity and causes the engine to run hotter, potentially triggering overheating. The coolant's specific heat capacity and the radiator's thermal mass are also factors — a larger coolant volume provides a greater thermal buffer against sudden increases in heat load.

External contamination reducing airflow: Insects, leaves, pollen, and road debris accumulate on the front face of the radiator and condenser (which is mounted directly in front of it), reducing airflow and cooling capacity. This is particularly common in spring and summer and causes higher-than-normal operating temperatures in traffic or towing conditions. The radiator can be cleaned from the engine side using low-pressure water.

Coolant leaks from the core or tank joints: The crimped joint between the aluminium core and the plastic tanks is a common leak point on high-mileage vehicles. Coolant escaping here leaves white or coloured mineral deposits around the joint. Internal corrosion from degraded coolant can also cause pinhole leaks in the core tubes. Any external coolant leak requires immediate repair — continuing to drive with a leaking radiator causes progressive coolant loss and eventual overheating.

Internal blockage from scale or corrosion: Corrosion products from degraded coolant, or mineral scale from incorrect coolant mixing with hard water, can deposit in the narrow radiator tubes, restricting flow and reducing cooling efficiency. A partially blocked radiator may allow the vehicle to maintain temperature at highway speed but overheat in heavy traffic when the engine load and ambient temperature are high simultaneously.

Level 1 — External Inspection: Inspect the radiator front face and the fins for debris accumulation at every oil change. Gently rinse the core from the engine side with low-pressure water to remove accumulated insects and pollen. Do not use a pressure washer directly on the fins — high pressure collapses the soft aluminium fins, reducing airflow. Inspect the tanks for cracks and the core-to-tank joint for coolant deposits indicating a slow leak.

Level 2 — Coolant Replacement: Flushing and replacing coolant every 50,000 km or 3 years is the primary radiator maintenance action. Degraded coolant becomes acidic and deposits corrosion products (typically a brown or black sludge) inside the radiator tubes. Using the manufacturer-specified coolant type mixed with distilled water prevents scale and corrosion. Never top up with tap water — mineral content causes scale deposits that progressively block the radiator tubes.

Level 3 — Professional Radiator Replacement: Radiator replacement requires draining the cooling system, disconnecting the inlet and outlet hoses, removing the cooling fan if mounted on the radiator, and disconnecting the transmission cooler lines if the transmission uses the radiator's integral oil cooler. Drain and dispose of the old coolant correctly — it is toxic to animals. Refill with the correct coolant mixture and bleed air from the system to prevent airlocks.