How To Repair a Radiator Leak

A car radiator is responsible for keeping the engine cool enough to function properly, by dispersing excess heat. As your car’s coolant flows around the engine, heat is passed to the coolant. The now-hot coolant then flows into the radiator, where thin metal strips called fins allow the heat to be transferred into the air quickly thanks to their large surface area.

A working radiator is essential to the sound function of your vehicle, so it’s important to keep an eye out for any leaks and act quickly to fix them. Below, you’ll find the steps to follow to fix a radiator leak, and what to do if the leak is too large to patch up.

Signs your car radiator is leaking

Before you attempt to fix a leaking radiator, you’ll want to be sure that that’s what the problem is. Here are the common signs that your car radiator is leaking:

  • Your engine overheats more often
  • Your coolant level has dropped quicker than usual
  • There are drops or a puddle of liquid underneath the engine
  • The car radiator is hissing

How to fix a leaking car radiator

Car radiator repairs can be simple, if the leak is small enough to patch up with a specialised car radiator sealant. This fluid contains non-ferrous fibres and active agents which can plug hairline cracks and pinholes.

Wynns Radiator Stop Leak is compatible with all antifreezes and coolants, and is formulated to plug cracks or leaks without clogging your car’s radiator waterways or temperature sensors. It also gives you extra protection against rust and corrosion, to help prevent any future leaks.

Important: Always ensure that your engine is cool before working on the cooling system. Serious injury can occur.

It’s quick and easy to add to your coolant system:

  1. Shake the bottle well.
  2. Pour the entire bottle into the cooling system via the radiator filler cap - this is a pressurized cap found near the top of the radiator. It’s often labelled on newer cars, but if you’re unsure, your owner’s manual will tell you where to find it. If your radiator is completely closed off and has a through-flow system, you can add the sealant via the coolant expansion tank.
  3. Close the system and let the engine run for around 10 minutes to give the sealant time to work.

Hairline cracks and pinholes should be fixed by adding a radiator sealant. However, if the leak is larger than a crack or tiny hole, then you’ll need to replace the entire radiator.

How much is a new car radiator?

The cost of a new car radiator will depend on the make and model of your vehicle. Thankfully, you can find a range of car radiators online at – to find the perfect fit for your car, just enter your registration number.

Once you’ve selected the right part, you can use our convenient click and collect service to pick up your replacement car radiator ready to fit. Or let us bring your part right to your door with our home delivery service.

If you’re not sure which car part is right for you, or just want a helping hand, then visit your local Halfords garage where one of our colleagues will be happy to help.