Is your car’s radiator leaking? Rather than paying for expensive repairs, you can use Holts Radweld to fix small holes in your car’s cooling system and achieve a permanent, professional repair.

Sound too good to be true? It isn’t. Developed by our specialist lab team, Radweld is proven to seal car cooling systems, repairing leaks without risk of clogging or blockages. In fact, it’s one of our most popular products, and drivers and mechanics alike have been using it for decades to repair leaks in car radiators.

If you’re keen to find out more about using Holts Radweld, this guide has you covered. We’ve outlined how it works and how to use it, and answered some common queries about how to get the best from our innovative cooling system repair product.

Use the links below to get the help and info you need or read on for the full guide.

What is Radweld?

Radweld is a cooling system stop-leak product designed to repair failures in vehicle cooling systems. It circulates through the cooling system to locate and repair small holes and cracks, resealing it to prevent further leaks and corrosion.

These failures can occur via internal corrosion after using poor quality coolant/antifreeze, or through failure to follow the appropriate coolant change schedules. Or they could simply occur through external damage to a component of the cooling system.

Radweld provides a permanent repair for small faults in the cooling system, including the hoses and radiator. It seals without damage or clogging and can be used in all cars and with any type of coolant/antifreeze.

How Does Radweld Work?

Radweld works its way through the system seeking out leaks and forming permanent repairs in minutes. The product has been carefully formulated to mix with all engine coolant and antifreeze. You pour it directly into the cooling system, no need to drain or flush the system first. Radweld also provides anti-corrosion protection and prevents future leaks; it will last the lifetime of the coolant in the system.

How to Use Radweld

  1. We recommend you let the engine cool before use.
  2. Remove the cooling system cap.
  3. Shake the Radweld bottle and pour into the cooling system.
  4. Run your car’s engine for 15-25 minutes with the heater on and check to see that the leaking has stopped.
  5. Finally check your car’s coolant level. If it’s less than the level recommended by your vehicle’s handbook, then top it up as needed.

Holts Radweld FAQs

Have a question about using Holts Radweld? Or want to know more about how it works? We’ve answered some common queries about the product below.

What holes and cracks does Radweld seal?

To provide an exact answer, Holts Radweld is designed to fix holes with a diameter of 30 thousands of an inch (or 0.762mm) and cracks with dimensions of 10 thousands of an inch (0.254mm) by half an inch (12.7mm).

This is what the industry has decided is representative of cooling system failures. That doesn’t mean you need to go out and measure the size of the hole or crack that is causing a leak. Radweld complies with the relevant tests, and we’ve also validated this with our own vehicle testing.

In fact, you don’t even have to find the leak – we’ve done the hard work, so you don’t have to. Just pour in Holts Radweld and go.

How long will Radweld last?

It’s permanent for as long as it’s in the system. It’ll also prevent any further corrosion in the system and prevent any further leaks from occurring. You can even use it as a preventative measure if you’re so inclined.

Can Radweld be used in any car?

Absolutely, and our products are not just for cars. Any vehicle with a cooling system can be susceptible to leaks. So, whether it’s a small car, large car, an SUV, 4×4, motorbike, van, or even static agricultural equipment, if it has a wet cooling system with a leak – pour in some Holts Radweld to get things running again.

How does Radweld seal holes without causing clogging or damage?

Obviously, we can’t give away any formulation secrets here, but we’ve come up with a smart solution to this. It’s trying to summarise years of formulation development work into a few sentences. So, without getting deep into the chemistry, think of the actives as a mixture of a sticky material combined with a number of different particulate materials.

We very carefully control the level of sticky material and the size of the particulates in order to achieve a balanced binding at the site of the damage, to make sure we seal those holes that we want to seal, and ensure we don’t cause any blockages. All our formulations are then rigorously tested so we know the theory works in practice for both sealing and damage prevention.

How does Radweld differ from Radweld Plus and Wondarweld?

The differences relate to usage and capability.

Radweld is compatible with coolant. Just pour and go. It seals holes in radiators, hoses, and the heater matrix. It will treat systems up to 14L capacity.

holts radweld plus in use

Radweld Plus is also compatible with coolant. Just pour and go. It seals holes in everything that Radweld does, and also seals leaks in the engine block (coolant to air leaks), cylinder head gasket, freeze plugs and water pump gaskets. It will treat systems up to 21L capacity.

Wondarweld is not compatible with coolant, so you need to drain and thoroughly flush the system before using. It has increased capabilities, but using it requires a little knowledge and a couple of tools. The benefit of Wondarweld is that it can repair much more severe cracks in the engine block and/or cylinder head.

wondarweld radiator repair main

Want to learn about other products in the Holts DIY car maintenance range? Visit the homepage to browse the complete range, or get more tips and advice on the Holts UK motoring blog.