How to repair a car radiator leak

Updated April 17, 2017

A radiator is an essential part of an automobile's liquid cooling system that must function properly to prevent the engine from overheating. A leaky radiator can lead to a costly mechanical meltdown, so it's important to discover and repair this problem as soon as possible.

Look for signs of coolant leakage on the garage floor, driveway or ground under your vehicle.

Check the level of coolant in the overflow reservoir or inside the radiator by removing the radiator cap. The engine must be cool before the radiator cap can be safely removed. If the coolant level in the overflow reservoir or radiator is unusually low, odds are good that you have a leaky car radiator.

Inspect the radiator to find where it is leaking. There may be an obvious hole or other defect that is easy to spot, such as deposits of coolant and an orange or green discolouration.

Remove the radiator for further testing if the leak cannot be found.

Use a radiator pressure test kit to fill the radiator with the amount of air specified by the radiator cap. Submerge the radiator in a tank of water and watch for escaping air bubbles. The source of these bubbles is the leak that must be repaired.

Pour the stop-leak additive into the radiator to fix small leaks, following the instructions on the product label.

Use a soldering iron to patch larger defects in radiators made of copper and brass, which are frequently found in older models. An epoxy gun may do the trick for the aluminium radiators in newer vehicles.

Refill the vehicle's cooling system after the radiator leak is repaired.


Some motorists keep a jug of water and a jar of black pepper in their vehicle for stopgap repairs of leaky radiators. Pepper expands in water and may temporarily plug a small hole in a radiator. This should only be done in an emergency. Consult a mechanic who is familiar with cooling systems before trying to repair a radiator leak.


Never drive a vehicle if you know it has a leaky radiator. Overheating can occur rapidly and lead to severe engine damage.

Things You'll Need

  • Radiator-pressure test kit
  • Stop-leak additive
  • Soldering iron or epoxy gun
  • Engine coolant
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About the Author

Kirk Brown is an award-winning freelance writer with two decades of diverse media experience. A former newspaper reporter and editor, he also was managing editor of an acclaimed scuba diving magazine. Brown has written scripts for more than 50 half-hour TV programs focusing on technology and health topics.