Seal It and Forget It: How to Identify a Coolant Leak in Your Car and Seal It Like a Pro

Your car’s radiator keeps the engine purring at the right temperature. But a coolant leak is a problem. Here’s how to identify a leak and seal it like a pro.

Image Top Hose Coolant Leaks

It’s easy to take your ride for granted. You get in, turn the key and go. Throw a quart of oil in now and then and you figure your maintenance program is complete.

Until the day you’re sitting at a red light performing car karaoke and notice smoke pouring out from under the hood. 

Either your radiator randomly sprung a leak or maybe it’s been slowly leaking coolant for weeks and you had no clue. So you sit there, hands frozen on the wheel and wonder if you should keep driving or phone a friend.

We can’t tow your ride, but we can help you figure out the problem.

Read our definitive guide on detecting and sealing coolant leaks in your car. Hint: Sometimes your car gives you clues before the engine overheats.

Watch the Gauges

If you don’t pay attention to any other gauge on your dashboard at least pay attention to your temperature gauge.

The first clue of a problem with the cooling system often comes from the temperature gauge. A high temperature gauge reading could indicate a loss of coolant.

Never ignore a high temperature gauge reading because it could mean your engine is overheating. And overheating engine usually leads to a towing charge.

In newer model cars, the check engine light may also be an early indicator of a cooling system problem. Pay attention when it comes on and then take the car to a mechanic, so you can have the error codes read.

The temperature gauge is relatively reliable as far as warning you of a possible leak. Be aware there are other reasons why a gauge gives a hot (or cold) reading that has nothing to do directly with a coolant leak.

A puddle under the car should be your next clue.

Don’t Ignore Puddles

If you’ve ever noticed a puddle of fluorescent green or orange fluid under a car, you’ve seen coolant.

You assume if the puddle isn’t large, you’re fine. Wrong. Anytime you see coolant under your car, it’s a bad sign.

The cooling system is a closed system and while it allows for evaporation, if you see coolant on the ground, you have a leak.

Now don’t panic every time you see a puddle under your car. When you run your AC you’ll see condensation in the form of a puddle. It could also be from a car belonging to another driver.

The smart thing to do if you notice a puddle is to check your coolant reservoir.

Check Your Coolant

If you weren’t aware, the coolant reservoir is not your radiator but it is a vital part of the cooling system.

The coolant reservoir stores excess coolant fluid until it’s needed. If you’re not sure where it’s located, find your radiator hose. Follow it from the radiator to the reservoir.

Voila! It’s a plastic receptacle and usually has a low and a high fill mark. Your coolant reservoir is also the first place you’ll be able to notice a leak.

If you have a coolant leak the level in the reservoir won’t get to the high fill mark, even when the vehicle is warm. If you notice low levels of coolant in the reservoir, take a minute and top it off before driving.

Check Your Hoses

If you’re even more convinced you have a leak, check your hoses. Hoses are the number one cause of coolant leaks.

Most vehicle cooling systems have 4 main hoses:

· Upper radiator hose
· Lower radiator hose 
· Heater hose (2)

If you detect a leak in any of the cooling system hoses, you’re in luck. They don’t cost much to replace and you can probably switch the culprit out by yourself. If the hoses look good, move on to the radiator.

Inspect the Radiator

So far, you’ve checked your coolant, watched for puddles of fluid under the car, and checked out the hoses. Now it’s time to get up close and personal with your radiator.

The simplest test for a leak in or near the radiator is the cardboard test.

Place a piece of cardboard under your car and check it in the morning. If the leak is in the radiator, you’ll see coolant on the cardboard.

The outside appearance of the radiator often tells the story as well.

If there’s a coolant leak, coolant and water escaping from the radiator can cause rust development. If you find rust spots, check also for visible signs of radiator fluid.

Mystery Solved

If you’re fortunate enough to find a leak without any further testing, you can move on to the next step.

But first, aren’t you curious why a radiator springs a leak? Look where it’s located—at the front of your vehicle. The radiator takes a beating from rocks and other debris you pick up on the road.

Also, if you don’t flush it on a regular basis, it can develop corrosion from sludge build-up. Corossion often leads to coolant leaks.

A leaky radiator allows draining of your coolant to the point where your engine overheats. The good news? All it takes to avoid a costly engine repair is to plug up the leaks with a radiator stop leak product.

It’s Not the Radiator

If your radiator seems fine, consider the engine block. The engine block can develop small cracks, which allow a coolant leak.

You may feel like Sherlock Holmes at this point, but persistence pays off and can save you from a major repair bill.

If you think you could have a leak from the engine block, try a cooling system sealer before you go into an all-out panic. Cooling system sealers act like little detectives. They flow through the cooling system until they discover the leak or leaks. If you have multiple cracks in the cooling system, the sealer fills all of them in.

It’s quick and gets your car back on the road—probably for many more years.

Coolant Leaks Aren’t the End of the World

They can be hard to track down but if you’re diligent, you’ll eventually find a coolant leak. 

Most drivers panic when they see coolant on the ground or have an engine light ringing the alarm. Remain calm and go through the steps listed above.

Once you narrow down the leak, seal it up and forget it.

For more information on all of our cooling system products, click here.