How to Stop a Leak in a Cooling System


A leak in your vehicle's cooling system can cause a variety of problems, some of which can seriously harm your engine if left unrepaired and allowed to worsen. The first step to fixing the leak is finding where it is located. The difficulty of repairing a cooling system leak depends on the type of vehicle and where the leak has occurred, as well as why the leak has occurred.

  • Determine that your cooling system is leaking. One sign of a leak is that your engine overheats while your are driving. Check your radiator to see if the vehicle is low on coolant. If you can't see coolant when you remove the radiator cap, your radiator is low on coolant.

  • Determine the location of the leak. Add coolant to the radiator and see if you can see any water leaking out. Crawl underneath the vehicle and look for puddles or drips of coolant. Check hoses coming in and out of the radiator for leaks or tears.

  • Identify the component of the radiator that is leaking. Common leak sites include the radiator itself, the water pump, the thermostat, the heater core and the head gasket. Leaks from the radiator, water pump and thermostat will be visible under the engine compartment. The heater core will leak inside the vehicle into the floorboards (a common cause of wet carpet), usually on the passenger side. The head gasket will cause coolant to leak into the engine oil, giving the oil the appearance of a chocolate milkshake when you check the dipstick. If you are unable to identify the leaking component, take the vehicle to a mechanic to have it properly diagnosed and repaired.

  • Replace the leaking component with a new, properly functioning component to stop the leak. The replacement process will vary by component and car.

Tips & Warnings

  • There are some products on the market that claim to be able to stop leaks in the radiator and cooling system, however these products are not manufacturer tested or approved and should be used at your own risk. They may damage your vehicle and void your warranty if used.
  • Antifreeze (coolant) is extremely toxic. Puddles of leaking out antifreeze can be fatal if an animal drinks them. Do not allow animals or children to come in contact with antifreeze.

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