The radiator dissipates heat from the engine coolant, allowing the engine to maintain proper operating temperature. When it fails (typically through corrosion, internal blockage, or external damage), the engine overheats and can suffer serious damage. Replacement is a moderate DIY job that varies in difficulty depending on access.
Symptoms of a Failing Radiator
Coolant leaks visible at the bottom of the radiator, in the plastic side tanks (a common failure point on modern radiators with crimped tank-to-core seams), or from the upper or lower hose connections. Engine overheating despite a working water pump and thermostat. Steam visible from under the bonnet. Coolant loss with no visible external leaks (sometimes coolant evaporates from a slow leak before you see it). Brown or rust-coloured coolant indicating internal corrosion. A bent or damaged radiator core after a front-end impact. See our overheating guide for related diagnosis.
Replacement Procedure
Drain the cooling system through the radiator drain (petcock) at the bottom or by removing the lower hose. Capture the coolant in a suitable container – it is toxic and must not be poured into stormwater drains. Disconnect the upper and lower radiator hoses by loosening the hose clamps. Disconnect the transmission cooler lines if the radiator has integrated transmission cooling (common on automatic transmission vehicles – the lines run to a separate cooler in one of the radiator tanks). Plug the lines to prevent fluid loss. Disconnect the cooling fan electrical connector if the fan is mounted to the radiator.
Remove the radiator support brackets or upper mounting bolts. The radiator typically lifts straight up out of the lower mounting cradle. On some vehicles, the cooling fan and shroud need to be removed first as a unit. Lift the old radiator out, install the new one, and reverse the procedure to reconnect everything. Refill the cooling system with the correct coolant type (your workshop manual specifies which – mixing types causes problems), bleed any air from the system, and run the engine to operating temperature while watching for leaks.
Aluminium vs Plastic Tank Radiators
Most modern radiators use aluminium cores with plastic side tanks crimped on. The plastic tanks are the most common failure point – they crack from heat cycling, especially around the upper hose neck. All-aluminium radiators (with welded aluminium tanks) are more durable but more expensive. For a vehicle you plan to keep long-term, an all-aluminium replacement is worth the extra cost.
Radiator capacity, coolant type, mounting hardware, and bleeding procedures are vehicle-specific. MechanicMate offers PDF workshop manuals for over 960 models at mechanicmate.net/shop.
— MechanicMate . Questions or a second opinion? [email protected].