• Formulated with a base of fibre materials
  • Safe for seals and hoses
  • No effect on metals, including aluminium
  • Safe to use in all radiators
  • Compatible with all corrosion inhibitor

Radiator Stop Leak

Nulon Radiator Stop Leak (R50) is formulated to effectively seal leaks in radiator and heater cores, weeping cylinder head gaskets and to temporarily repair corroded welsh plugs.

Nulon R50 is formulated with a base of fibre materials. Safe for seals and hoses, has no effect on metals, including aluminium, and is safe to use in all radiators. R50 is compatible with all corrosion inhibitor and all other anti-freeze/anti-boil products.

Note: If the cooling system is dirty or restricted, first clean it with Nulon R40 Radiator Cleaner. 

NOTE: EXERCISE CAUTION when removing radiator cap if engine is hot.

  1. Before adding this product, fill coolant to above top radiator hose
  2. Start engine and turn heater on
  3. Run engine until normal operating temperature is achieved
  4. Shake bottle well & add slowly to radiator
  5. Top up coolant & refit radiator cap securely
  6. Run engine for 15 minutes to allow product to circulate
  7. Inspect for leaks

Application Rates

Add 1 bottle for every 10 litres of water or part thereof. To protect cooling systems against corrosion and electrolysis use Nulon R45 Ultra Cool Concentrated Radiator Treatment or one of Nulon's Long Life Coolants.


Radiator stop leak products should only be used as a temporary repair. You should have a mechanic check and repair the problem at the first available opportunity.




Often when a cooling system has overheated and boiled, scale and sludge within the system is dislodged and can easily block the core of a radiator that was previously functioning satisfactorily. The sludge and scale can then quite easily cause a blockage in the radiator core when the engine is next operated. Always be aware of this possibility. If such a problem occurs, the best course of action is to have the radiator professionally removed and cleaned.

Part numbers

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Radiator Stop Leak
Part No.R50

300 ml bottle
6 per carton

Barcode: 9311090000179

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