Despite their small size, pinhole leaks in a radiator will still cause your car to lose large amounts of coolant or fluid when driving. The best way to permanently stop these leaks is to take your car to a mechanic, who will then use a sealant to patch up the leak. You can also buy the sealant and patch the leak itself, although it is recommended to let a mechanic handle the job. In some instances, it is necessary to temporarily stop a leak in order to get your car from point A to point B (to the mechanic's shop, for example). In such circumstances you can use simple steps to clog the leak long enough to get to your destination.
Determine whether the leak is coming from the radiator hose or the radiator itself. This is typically done by examining upward from the puddle of leakage that has emanated from the car. Holes may be easily visible, and sometimes you will be able to see a radiator or radiator hose dripping. Other times you may have to disconnect the hose from the radiator and run water through it to see if there is a leak. If there is not, the hole is in the radiator itself.
Patch a hole located on the hose with duct tape. Using several layers will allow the hose to stay leak-free long enough for you to buy a new hose and replace the faulty one.
Unscrew the radiator cap if the leak is directly inside the radiator. To eliminate risk of burning yourself, do not touch the radiator cap until you know the system has cooled down.
Pour 2 teaspoons of ground pepper inside the radiator, then add water. Water will cause the pepper to swell and block the leaking hole.
Screw the cap back onto the radiator.
