How to use Thurmo Stop-Leak radiator sealant

Seals quickly and permanently leaks in your car radiator


1. Check that there is enough water or anti-freeze in the radiator.

2. Put Thurmo sealant directly into a radiator filled with warm water or anti-freeze (not in the expansion tank). When opening the radiator cap, be cautious with possible hot liquid in the radiator.

3. Start the engine (you can start driving) and let it run about 10 minutes. When the engine warms up the sealant dissolves in the hot radiator liquid, finds its way to the leakage areas and fills the leak with a metallic temperature variation proof seal. The seal produced on the outside of the leakage area is soft at first but hardens to a permanent seal due to the effect of heat and air.

When using Thurmo Stop-Leak make sure that your radiator system of your vehicle is not clogged. For best results, radiators older than 2 years should be rinsed and cleaned before use.

Please note!
Do not mix Thurmo Stop-Leak with other products. If you already have used another product without success it is advisable to remove the remnants from the system before applying Thurmo Stop-Leak.

As Thurmo Stop-Leak contains lubricants and anti-corrosion components it is gentle to even the most sensitive parts of the radiator. In the circulating system Thurmo Stop-Leak seals even the possible future cracks. Thurmo can be used both with normal anti-freeze as well as water.


Passenger cars:
1/2 of the packet’s content to smaller leaks, 22g or more to more extensive leaks.

Larger vehicles such as trucks:
22 g to every 10 litres of radiator liquid.