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Radiator Leak? Here Are the Next Steps

An old radiator that has suffered from a radiator leak

There are no two ways about it — a radiator leak is nothing to treat lightly. When you see fluids that are supposed to stay inside your car on the outside, there’s trouble. Here we’ll cover how a radiator operates and how to solve the problem of a radiator leak.

A Breakdown of the Basics

The engine cooling system in your car works by pumping a liquid coolant (usually a mixture of water and antifreeze) through channels in your engine block. The liquid absorbs heat from the engine and carries it out into the radiator, where it is cooled by fans before being recirculated back into the engine.

Puddles and Streams

In the old days, a puddle of coolant on the ground was a fairly common sight, especially on hot days when a car had been running with the air conditioner on. But environmental regulations and concerns for pets and wildlife resulted in coolant overflow tanks becoming standard equipment decades ago, as the ethylene glycol in coolant is deadly to animals. So if you see coolant on the ground, something’s wrong.

Detective ModeDEN-2210508 automobile radiator

Before you do anything, make sure the radiator is cool by turning off your car for at least a half hour. Next, check the hoses and fittings. If they’re wet, one of them is the culprit. Luckily, these are relatively easy to seal or replace.

If these components aren’t causing the issue, you might have a more serious leak in the system. Check for signs that the radiator fins are clean. If they have coolant on them, look for a leak along the seams or any welded parts. Check the filler neck to see if coolant has run out and dripped to the bottom.

If you don’t see any evidence of this, it’s possible that you have a leak that only manifests itself when the system is running and under pressure. It’s important that you wear safety goggles when you’re checking for this kind of issue, as when the engine hits operating temperature, coolant can spurt out.

What Now?

If you find a radiator leak, get your car to the shop for repairs immediately. A catastrophic radiator or cooling system failure can do enormous and expensive damage to your engine. If a shop is more than a couple of miles away, have your vehicle towed. If you have to drive, drive gently. Keep the cabin heat on high to vent heat from the engine, and keep a leak-stopping additive in the trunk. Don’t use this unless it’s absolutely necessary, or else you’ll need a complete radiator and system flush in addition to the repair.

Radiator leaks usually start small and get bigger, so make sure you scan the ground around your car regularly, perform required tune-ups and flush the radiator system according to the recommended schedule in your owner’s manual.

Check out all the radiator products available on NAPA Online, or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on radiator leaks, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photos courtesy of Wikimedia Commons.


Mike Hagerty View All

Mike Hagerty is an automotive journalist whose work has been featured on radio, TV, in print and online since 1997. He's the Publisher and Editor of, and contributes car reviews to the Los Altos Town Crier and Previous outlets have included KFBK and in Sacramento, California, the ABC television affiliates and Hearst-Argyle and Emmis radio stations in Phoenix, Arizona; AAA magazines for Arizona, Oklahoma, Northwest Ohio, South Dakota and the Mountain West and

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