What Causes a Car Radiator Leak?

Your radiator is responsible for cooling your engine and keeping it running at the proper temperature. A leak in your radiator not only creates a risk for overheating and engine damage, but it also creates a potential risk of engine fire. It’s important to do occasional checks of your radiator and cooling system to address any leaks as soon as you detect them.


Where Radiator Leaks Can Occur

There are several possible locations and causes of radiator leaks:

  • The radiator core itself. Most automotive radiators consist of long tubes welded into a header, with tanks at either end and fins between the tubes for air cooling. Modern radiator cores are typically made from aluminum, but older vehicles may feature copper. Thermal expansion, vibrations, impacts and corrosion can all degrade a radiator, and eventually cause leaks.
  • The radiator tanks are another potential source of coolant leaks. Depending on the construction of your radiator, your tanks could be directly welded to the radiator core or be crimped plastic tanks that make use of a rubber gasket. In all cases, cracks can allow coolant to escape. It can be difficult to inspect your tanks, as most radiators are difficult to access from under the hood of your vehicle.
  • Your radiator hoses, tubes and filler neck can leak as well. Rubber radiator hoses are susceptible to getting dry and cracked, especially on older cars or ones that sit for a long time without being used. Clamps and clips can wear out over time, and they might allow leaks where the hoses attach to your radiator. Your radiator cap needs to be inspected from time to time, as the spring can weaken and allow coolant to leak.

If you detect a coolant leak at any of these locations, it’s important to repair it quickly. No coolant leak will stay small for long, and a major rupture can leave you stranded on the side of the road.


In all cases, it’s important to be careful when you’re inspecting your radiator. Always start with a cold engine to see if any coolant leaks are present at rest. Once you start your engine, your coolant is pressurized and can erupt from a leak and injure you. At operating temperatures, this coolant jet can be hot, causing serious injury. Always wear safety glasses and proper clothing and avoid getting too close to your coolant circuit.

Don’t Let a Small Leak Become a Big Leak…and a Big Problem

No engine coolant leak will stay small for long – they worsen and expand by nature. Due to the pressures and temperatures in your coolant circuit, a leak will inevitably become bigger and bigger, until you’re left stranded on the side of the road. In a few cases, like with major damage or corrosion, the only solution will be to physically replace your radiator. Thankfully, most of the time a quick and cheap application of a Bar’s Leaks cooling system repair product is all it takes to repair your coolant leak and keep your engine running cool for many more miles. We’ve been the cooling system experts for over 60 years, and we’ve sold more products in this category than anyone else on the market.

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