To stop pinhole leaks, first identify the leakage source, and use electrical or duct tape to cover the pinhole in a radiator or pipes. In case of a radiator, use black pepper to block a hole, and in case of pipes use a rubber gasket along with a clamp for the purpose.
To stop pinhole leaks in a radiator, check whether the leakage is inside the radiator or in its hoses. Then, switch off the engine of the unit, and cool it for half an hour.
If the leakage is in the hose of the radiator, cover the pinhole using electrical or duct tape. Be sure to wrap the tape tightly around the hole. After one week, replace the hose of the radiator.
If the leakage is in the radiator, take out the cap of the unit, and put two teaspoons of black pepper in it. When the pepper comes in contact with water, it swells up to plug the pinhole. Then, fill the reservoir of the coolant fully, and replace the cap of the radiator.
To stop pinhole leaks in pipes, turn the pipe's valve off, and wipe the area, using a towel to dry it. Cover the pinhole with a few layers of electrical tape. Ensure that the tape covers an area of 6 inches on both sides of the pinhole.
Then, position a rubber gasket on the hole, place the clamp on the gasket's pipe, and tighten the clamp's screws so that it is secured to the pipe.