Radweld – The Science behind the Product

Our lab team at Holts are passionate about making our products the best for you, so we spoke to them about Radweld, so that you can understand the science behind one of our leading products.

Read on for more information about how our lab team develops and tests Radweld to ensure it works in your car when you have an emergency, or click below to view Radweld.

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What is Radweld?

Radweld is a cooling system stop-leak product designed to repair failures in vehicle cooling systems.

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.

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Can you tell us a bit about the process for testing Radweld at the lab?

The engine cooling system is one of the most critical systems in any vehicle. If it stops working properly, the average engine can produce enough heat to melt the block in around 30 minutes, and obviously could cause significant damage quicker than this.

Its importance is recognised by the global industry and therefore cooling system stop-leak products must comply with three American Society for Testing and Materials (ASTM) methods in order to prove their capability and suitability for use in engine cooling systems.

We follow the three tests and the combination of the results provides us with data to be sure that the products will do what we say they will, and also that they don’t cause any harm to the engine cooling system. These tests are;

  • ASTM D-3147 – this describes how to test the sealing ability of the stop-leak formulation. We’ve had a test rig specifically designed and built so we can make sure our formulations seal the holes they should, and don’t cause any blockages to the radiator fins or heater matrix.
  • ASTM D-1881 – this describes a foaming test. If the stop-leak product causes foaming in the cooling system, that will reduce its heat transfer properties and cause overheating. We need to make sure we fix the problem without causing another, so compliance with this test method is a crucial element of the testing that not many people are aware of.
  • ASTM D-6107 – in order to pass this test method, the product must obtain specific minimum pass criteria on the two tests mentioned above. It must seal holes and slots of a specific size (representative of leaks in cooling systems), and not seal holes of a larger size (representative of radiator fins and heater matrix cores). As well as meeting these criteria, after the end of the sealing test on ASTM D-3147, the coolant mixed with the stop-leak product must pass through a fine sieve (which is an ASTM E-11 No. 10, in case you’re interested!) without leaving any particulate or residue.

Car head gasket Bruce Ellis and Rich

As well as the industry standard tests, we also conduct tests on vehicles with cooling system leaks to ensure we have a wide and deep data set that we are continually adding to.


Can you tell us about the kind of holes/cracks that Radweld seals?

I’ll give you the scientific answer first, and that is holes with a diameter of 30 thousands of an inch (or 0.762mm for the younger, more metric readers!) 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. As I’ve said we comply with the relevant tests but we’ve also validated this with vehicle testing and obviously those industry experts know their stuff!

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 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 pretty 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 ensures we don’t cause any blockages. All of our formulations are then rigorously tested so we know that the theory works in practise for both sealing and causing no harm.

 flush radiatior

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, which is exactly what I do – just in case!


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 you running again.


What about the other products in the range, Radweld Plus and Wondarweld? How are they different?

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.

Radweld PlusRadweld 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.

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