How to Fix a Coolant /Antifreeze Leak

There are few automotive gremlins as pervasive as a leaky radiator. Nearly everyone and their mothers have stories about waking up one fine autumn morning, going out to the car, and finding a massive pool of green liquid where a clean floor should be. We’ve all been there, it’s not fun.

A coolant or antifreeze leak can be caused by a number of things, ranging from poorly tightened hose clamps, worn hoses, or a box of rogue highway nails that turned your radiator into Swiss cheese. All of these can quickly turn your grocery run into a popped hood, steam belching, tow-truck necessitating day. You can, however, save yourself some time and money if you catch the issue early and repair it yourself.

Given that your car’s cooling is somewhat important to its overall health (Just kidding, it’s vitally important!), The Drive put together this guide on how to fix a coolant or antifreeze leak and answered all your burning questions along the way. Ready?

Antifreeze and coolant are engine fluids designed to keep your engine running at an efficient operating temperature, whether that’s keeping it from freezing or overheating. 

Antifreeze is concentrated is commonly made up of ethylene glycol and silica which, when combined with a predetermined mix of regular H2O, makes coolant and keeps your car’s engine cool and warm enough for most temperatures around the world. For those places with extreme cold, such as at the Earth’s poles, they use propylene glycol which will only freeze if the temperature drops to -74.2 degrees Fahrenheit. 

A coolant/antifreeze leak can occur for a variety of reasons, including a blown radiator hose, a bad hose clamp, warped head gasket, or the most common reason, a foreign object kicked up by the truck in front of you penetrating the radiator itself. The resulting cascade of fluid can overheat your engine, warp your heads, contaminate your oil, and leave you stranded on some lonesome highway. None of those options are good for your health or your car’s. It’s time to fix that.

Estimated Time Needed: One to two hours

Skill Level: Intermediate

Vehicle System: Heating/Cooling

Working on your car can be dangerous and messy, so here’s exactly what you’ll need to ensure you don’t die, get maimed, or lose a finger and that you keep your jeans, shirt, and skin spotless—hopefully.

We’re not snooping around your toolbox, nor rummaging through your garage, meaning we don’t know what you have in the way of tools and parts. So here’s a list of what you’ll need to repair a coolant/antifreeze leak.

Organizing your tools and gear so everything is easily reachable will save precious minutes waiting for your handy-dandy child or four-legged helper to bring you the sandpaper or blowtorch. (You won't need a blowtorch for this job. Please don’t have your kid hand you a blowtorch—Ed.)

You’ll also need a flat workspace, such as a garage floor, driveway, or street parking that’s also well-ventilated. Check your local laws to make sure you’re not violating any codes when using the street because we aren’t getting your ride out of the clink.

Now that you’ve safetied up and have all your tools ready to go, let’s do this! 

So you’ve found yourself in the middle of Montana. Every which way you gaze, there’s nothing but desolation which is unfortunate because your radiator just sprung a leak and has morphed  into a colander. What you do have, however, and we have no idea why, are a dozen fresh eggs in your back seat. You’re in luck, friends, as those unfertilized chicken products can help! Here’s what you do.

This old trick works as the heated coolant/antifreeze cooks the eggs and the pressure of the leak attempts to force out the cooked eggs, thereby stopping the leak until you can get it replaced. Science!

A car’s hoses are clamped down by hose clamps, little metal circles that feature some type of screw or other device to sinch them tight. And as the car ages or is used in a locale where rust is all but assured by yearly road salting, the hose clamps can fail and release coolant everywhere. Here’s how you can replace them when they do. 

As a car ages, the plastic and rubber hoses that feed the engine its vital fluids can snap, crackle, and pop, just like Rice Krispies. You’ll likely notice a few drops of coolant on the ground but that can quickly turn into a flood. When that occurs, you’ll need to replace them. 

As different automotive manufacturers have different locations and bracketry for radiators, The Drive picked the most common style (up front, mounted behind the car’s bumper) as our example. You’ll need to consult your handy-dandy, and likely dusty, owner’s manual to determine exactly how you can replace your specific radiator. 

Although The Drive’s detailed how-to guides are easy to follow, a rusty bolt, an engine component not in the correct position, or a messy oil leak can derail a project. That’s why we’ve partnered with JustAnswer, which connects you to certified mechanics around the globe, to get you through even the toughest jobs. 

So if you have a question or are stuck, click here and talk to a mechanic near you. 

Over the years, The Drive’s editors have seen murky pools of green liquid underneath our cars more times than we care to share. There was, however, one cross-country trip where a rock pierced our radiator and went air-cooled for about 1,000 miles—luckily it was the dead of winter and the outside temps hovered around 15-degrees. 

Here are our favorite tips, tricks, and hacks for repairing a coolant/antifreeze leak.

You’ve got questions, The Drive has answers!

A. You can, the author proved it, but you don’t want to make a habit of doing so. A small leak is manageable but can quickly become a serious problem, one that will cost far more than just replacing or repairing your radiator. 

A. That may be because it’s leaking from the radiator cap’s stem. At the top of the engine, there’s the radiator cap. Just below the cap is the step, the spot where you pour coolant/antifreeze in to. If that stem cracks, as the temperature of the coolant/antifreeze increases, it can bubble up and leak out of the stem, causing small leak. This wouldn’t be enough of a leak to cause your ride to overheat.

A. Don’t worry, asking is always ok here at The Drive. Here are a few symptoms of a blown head gasket, pay close attention to the last one. 

If a head gasket blows, even slightly, the engine might overheat and damage several components. One thing you should never do when your car is overheating: Remove the radiator cap and check the coolant. That’s how you get a one-way ticket to the ER for a scalded face.

If you notice milky colors in your oil, you might have a blown gasket—the underside of your car’s oil reservoir cap will likely become splattered with the milky oil. This happens when coolant comes in contact with and contaminates the oil. 

If you notice bubbling inside the radiator or coolant reservoir, it’s an indication your system has air in it, which could be caused by a leaking or blown head gasket.

A. Hahaha, no. A blown head gasket causes all sorts of issues downstream of the original issue and essentially means you need a new engine. You can try to prolong the car’s death, but it won’t change the, you know, deadly outcome. 

A. As you’re replacing an engine, it can cost anywhere between $1,000 for a junkyard four-cylinder to $22,000 as the author was quoted for a new engine for his 2004 Volkswagen Passat W8. Now imagine what a Bently would cost. Yikes.

A. Do you want to do it right or just get by for the time being? Because if you purchase one of the quick-fixes, you’re out about $20-$50. To properly fix the radiator, which means replacing the unit, a new radiator can cost between $300-$1,200 depending on the car, location of the radiator, and labor. 

A. It can, but it’s unlikely given most coolant/antifreeze is mixed with water. So there’s some silver lining!

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