Radiator Leak Stop

Determining if you have a radiator leak can be a major pain in the ass! It’s not always as easy as opening your hood and seeing a large crack in your radiator. Often times a brake leak or engine oil can be confused with a radiator leak. 

The first step is to determine what’s leaking? Radiator leaks often get confused with brake leaks and engine oil. After you have determined that it’s your radiator you’re going to need to locate the leak and determine if it’s fixable, sometimes the damage is just too big to fix and you’ll need a replacement.

There are many different methods to fixing a radiator, but we advise if you don’t have any previous mechanical experience you’re probably better off bringing your vehicle into a service station so a mechanic can properly fix the problem or install a new radiator.


If you’re the do it yourself kind of guy, which let’s face it, a lot of us are, you’ll want to tackle the problem yourself. Fixing a radiator with a small crack or leak can be relatively cheap and quick to do if you know what you’re looking for and the options available.

In this tutorial for How To Stop A Radiator Leak we’ll go over:

  • How To Determine What Is Leaking
  • How To Find a Radiator Leak
  • How To Fix a Radiator Leak

After reading through this article you’ll be ready to identify a Radiator Leak, find the source of the leak and fix it with a handful of different techniques from quick on the go temporary fixes to solid permanent fixes.

How To Determine What’s Leaking

Check Your Coolant Gauge Temperature

Locating a leak from your vehicle can become a pain if you don’t know what you’re looking for. To determine if your radiator is leaking there is multiple checks you can perform to pinpoint what’s your issue. If you’re driving while your radiator is damaged you can look at your dashboard.

Next, to your Speedometer, there will be a gauge for your coolant temperature, the fluid that is inside of a radiator. When a leak has happened and your engine is not getting enough coolant the temperature will rise. Look at the gauge, if it’s in the red or near the red you could have an issue with your radiator indicating you should look into it further.

Is There Green Or Orange Fluid Under Your Vehicle?

Quick checks include looking under your vehicle. When your radiator leaks it will commonly create a puddle of fluid under the front end of your vehicle. Make sure to not confuse other fluids that may be under your vehicle for coolant.

For instance, when you run your AC it produces condensation that will create clear puddles of water under your vehicle, or if you have an oil leak you could have a brown/yellow puddle of thick fluid.

Coolant regularly is green or orange in color and that is what you are looking for.

Mark Your Radiator Coolant Reservoir

If you haven’t found any fluid under your car or suspect the fluid you do see to be coolant from your radiator you can take a pen and mark a line on your coolant reservoir under the hood. Your coolant reservoir will have a min and max line on the side for easy identification.

Once you have marked your current level you can go for a quick drive around 30 minutes (depending on the amount of fluid in your reservoir, if your fluid is near the min line, top up to the max line before performing this check)

When you return and check your fluid, if it’s under the line you marked you can be sure there is a leak somewhere in the radiator.

Examine Your Radiator For Excess Rust

A spot check can also be performed without driving your vehicle any further. If your radiator has been leaking for a while you can look down in the engine bay under the hood for any abnormal rust around your radiator

(It’s common for parts to rust, but if your radiator has been leaking the rust will be very prominent compared to other parts of the engine bay)

If a large area is heavily rusted more than the rest of the engine components it can be another signal that your radiator has been leaking.

How To Locate A Radiator Leak

Safety First – Turn Off Your Vehicle And Step Away.

Once you have determined that it’s your radiator leaking the next step is to try and locate the leak.

There are many different methods and things to check on to find out where the leak is coming from. First and foremost whenever looking for a radiator leak ensure that you turn your engine off, open your hood and allow your engine too cool for a couple hours (until cool to the touch).

Radiators cool the engine hence they retain a lot of heat and at the same time pressurize, opening a radiator cap while the engine is hot or running can be extremely dangerous and burn you severely.

Always Wear Protective Safety Gear

Before checking your radiator it’s advisable to wear proper safety gear. We advise anyone performing test’s and examining their radiator to wear protective gloves and eye protection in the event there is still hot fluid in your radiator or if it is still pressurized and fluid sprays out.

Because radiators can get extremely hot, especially when there has been a leak, gases can build from the heat and pressurization. This is why we always advise allowing the engine to completely cool before performing any checks.

Rinse Down Your Radiator & Surrounding Engine Bay

To start checking for a hole or crack in your radiator start by rinsing off your radiator and components around it with your hose. There is no need for using soap. Whenever you introduce water into your engine bay make sure you do not directly spray electrical wires or wire harnesses (If any wires are too close to your radiator you can wrap them in plastic bags before beginning)

As well, whenever you spray water into your engine bay it’s extremely important to ensure the engine is cool, not allowing this to happen can cause engine components to crack from rapid temperature change and increase problems. Any extra grease that cannot be removed from the hose can easily be removed by spraying brake klean on to the area then rinsing off or wiping with a rag or cloth.

Turn On Your Vehicle And Look For A Leak

Now that your engine bay and radiator is clean, if you still cannot see or locate the crack that you suspect is in your radiator you can start your vehicle and look for a leak to begin. Always wear safety protection and use common sense.

Radiator fluid will steam out of the crack. Once the vehicle is running look for a leak to form by either looking under your vehicle or looking down at the radiator. If nothing is visible keep an ear open to listen for any hissing or dripping that may occur from the leak. (If the leak is very large radiator fluid can shoot out, always take precaution)

Perform A Radiator Pressure Test

Finally, you can purchase a radiator pressure tester that can be used. When the engine is completely cool open the radiator cap that is located on the top of the radiator. Screw on the pressure tester and pump up to 10 pounds.

If you have a leak your pressure should start to drop. (Make sure you do not over pressure the test, pressure should not go above 10 – 15 pounds or it can produce more damage) Look over all of the lines that come in and out of the radiator. After time rubber lines can degrade and produce holes and cracks that can also attribute to radiator leaks.

How To Fix A Radiator Leak

Commercial Radiator Leak Sealants

Once you have located and determined that you have a leak in your radiator it’s time to fix it. There are tons of different quick fix (temporary fixes) as well as more permanent fixes depending on the size of the hole or crack.

Commercial Leak Sealant all work the same for the most part. Start with the engine off and cool, remove the radiator cap and pour contents in. Top off with 50/50 coolant and water if your radiator fluid is low and then screw the cap back on.

Start your engine and allow it to run for 5 – 10 minutes or follow the directed time specified in the instructions from the sealant manufacturer.

The radiator leak stop will work its way through your radiator plugging any holes or small cracks along the way.

Once the allotted time has passed turn off your engine and allow it to cool overnight to allow the sealant to set. Most quick fix sealants are not a 100% permanent like epoxy or professional work will provide.

Using Epoxy To Fix A Radiator Leak

Another common method for repairing cracks and holes is to use epoxy. Epoxy can be used as a more permanent fix as well as used on slightly larger cracks and holes that conventional sealant will not fix.

Before beginning it’s important that everything is extremely clean. After everything is clean, rinsed and dried and the crack has been located use brake klean to remove all dirt and grease around the crack and allow to fully dry.

Knead epoxy to allow it to warm up for use, when spreading epoxy over the damage ensure it is at least ⅛’’ thick to compensate for the pressure that builds in the radiator when the vehicle is on. Allow the epoxy to set for at least 24 hours (read instructions on the epoxy) Radiator fix epoxy can be found in most auto parts stores and hardware stores.

Temporary Quick Fixes Using Eggs & Pepper

There are times that you don’t have any radiator leak stop or epoxy to fix your leak and you may be stranded on the side of the road. There are a few very temporary fixes that can be performed to allow you to get to the nearest service station.

Both at home radiator fixes are not advised to be performed because both can cause further issues, but in times of need, they have been proven to get you back on the road until you can find a service station.

Egg Radiator Sealant –

Eggs can actually be used to temporarily fix a radiator leak, the yolk of an egg can work its way through the radiator and expand and plug any leaks allowing you to drive for short amount of time. To do this method again allow your vehicle to fully cool to the touch. Take 2 – 4 eggs and separate the yolks from the egg whites and pour the yolks into your radiator, top up your radiator coolant and you’re set. Continue driving to get to the nearest service center and the egg yolks should plug your crack – this method is not advised in most cases because the eggs can clog lines in your radiator and hoses further complicating issues.

Pepper Radiator Sealant –

Pepper is another odd fix that you may not have thought of ever using but it can be just effective as using an egg yolk. The pepper method is best used for only very small pinhole leaks but nonetheless, it can be used. Following the same steps as the egg yolk it can be quite effective but again, it is only a very temporary fix that is supposed to get you from point a to point b to get a proper repair

Setting Time

Allow Time To Set

Now that you are finished doing your repairs you need to allow time for setting. Radiators are under constant strain from heat and pressure, a crack that has been sealed and not given proper setting time is sure to continue leaking in a short amount of time. Whether you used a commercial sealant or epoxy you will want to allow your fix 24 – 48 hours to fully cure, reference your instructions from the leak sealant package for further setting time instructions.