The radiator hose is a rubber hose that carries the hot cooling fluid from the engine to the radiator, where it can be cooled prior to recirculation back to the engine. The hose is typically a flexible rubber hose that has been moulded to fit the specific application. Exposure to high heat from the engine and chemical attack from the coolant can cause the hose to fail. If this happens, the car cannot be operated until the hose is repaired or overheating of the engine can result. In an emergency situation the hose can be temporarily patched, allowing the car to be driven a short distance to a repair shop.
Carefully examine the outside of the radiator hose for perforations (cracks, holes, etc.). If none are visible, check the engine coolant level. If there is sufficient coolant (level is above minimum level marked on the coolant reservoir), start the engine. If coolant level is low, replenish the level with properly diluted coolant. With the engine running, dry the outside of the radiator hose with a rag and look for the reappearance of fluid or escaping steam. Be very careful not to directly touch the hot hose or hot engine components.
Carefully note the location of the leak.
Stop the engine and allow it to cool. Remove the coolant reservoir cap.
If the leak is within an inch or so of either end of the hose then disconnect the hose at the leaking end. Cut a long enough length from the end of the hose to remove the leak and then reinstall the hose. Replace the coolant reservoir cap, start the engine, and confirm that the leak has stopped.
If the leak is not near the end and you have a radiator hose repair kit, follow the instructions provided with the kit. Some kits consist of a hose coupling and hose clamps, in which case the leaking section of hose should be cut out and the two remaining sections rejoined using the coupler and hose clamps. Other kits provide a quantity of rubber patch material and high temperature rubber cement, in which case the hose should be cleaned and slightly roughened before affixing an external patch with the rubber cement. The reliability of an external rubber patch can be improved by placing a hose clamp over the patch.
Replace the coolant reservoir cap, start the engine and confirm that the leak has stopped.
If the leak is not near the end and you do not have a repair kit, patch the leak by first cleaning completely around the hose in the area of the leak, then wrapping several turns of duct tape around the leak. If you have a hose clamp, put it over the duct tape to reinforce the patch. Replace the coolant reservoir cap, start the engine and confirm that the leak has stopped.
Regularly inspect your radiator hose and replace it if it shows any cracking, blistering or other signs of deterioration. Keep a suitable radiator and heater hose repair kit in your car, especially if the hoses are old. Many kits are specific to a certain diameter of hose, so be sure you get a kit that will work on your particular hose diameter. Keep a roll of duct tape, a quantity of engine coolant fluid, impervious gloves, eye protection and an assortment of hose clamps in your car emergency repair kit. Some manufacturers produce a product called "Rescue Tape," or something similar, which is a special tape formulated for high temperature applications. This tape is superior to duct tape for radiator hose emergency repairs.
Do not touch hot engine parts. Do not loosen clamps or caps, and do not cut hoses when the engine is hot. The cooling system operates under pressure, and hot coolant can spray out of any leak or opening. Always allow the engine to cool until it is only warm to the touch before starting work on the cooling system. Limit exposure to coolant fluid by wearing impervious gloves. Protect eyes by wearing safety glasses. Do not breathe fumes. When removing sections of hose, either from the end or from the middle, do not remove more than an inch or so. Each hose is moulded to fit the specific application, and shortening the hose will cause it to be stressed, which in turn can cause cracking and failure. When tightening hose clamps on unsupported hose, be careful not to over-tighten and crimp the hose. This can stress the hose and create additional leaks. Do not drive unnecessarily with a repaired radiator hose. Once the hose has been repaired, have it replaced as soon as possible.