10 Best Radiator Sealant Leak Preventer in The UK

Last updated on 12/08/2025

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Best Choice

9.8

Exceptional

K-Seal

K-Seal HD Coolant Leak Repair, 472ml | HGV Radiator, Block & Head Gasket Sealant

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Why We Love It

No flushing required, simple.
Multi-purpose and permanent solution.
Compatible with all antifreeze.

Main Highlights

FIX IT FAST: Our multi-purpose solution works in minutes to quickly & permanently seal leaks in the radiator, head gasket, freeze plugs, block, heater matrix & water pump of heavy duty vehicles. Fixes most leaks in water-cooled engines.
STOP HOLES & CRACKS: With 1 step our unique formula will seek out each hole & crack, permanently sealing them, without any adverse impact on the efficiency of your engine cooling.
EASY TO USE: K-Seal couldn't be simpler & requires no draining or flushing; just shake, pour & go - shake the bottle, add the fluid to your coolant system & run your engine as normal.
HEAVY DUTY PERFORMANCE: Engineered for large engines & industrial use; suitable for commercial or agricultural vehicles. A permanent repair for the lifetime of the engine. Compatible with all types of antifreeze coolant.
PROFESSIONAL-GRADE RELIABILITY: Trusted by mechanics, our non-corrosive sealer delivers a durable & long-lasting repair, without clogging your cooling system. A cost-effective solution to engine coolant leaks, enhancing the reliability & performance of your vehicle’s cooling system. We've sold millions worldwide & are independently verified by university testing to meet ASTM D3147.

Holts SEALit Leak Repair 250ml - Professional Radiator & Coolant Leak Sealer for Engine, Cylinder Head, Head Gasket, Freeze Plugs, Water Pump Gaskets, Radiators Red - 1 Pack 250ml

Why We Love It

Quick and permanent leak seal.
Easy to use and effective.
Safety for engine components ensured.

Main Highlights

Professional Leak Repair: Seals leaks in engine blocks, cylinder heads, head gaskets, freeze plugs, and water pump gaskets quickly and permanently.
Easy Pour-and-Go Formula: No draining or flushing required—simply pour into the radiator or expansion tank for instant results.
Safe and Non-Clogging: Specially designed to work without clogging or damaging your engine, radiator, or cooling system components.
Corrosion Protection: Provides long-term protection against rust and corrosion, extending the life of your cooling system.
Compatible with All Coolants: Works with all types of coolant and antifreeze. One 250ml bottle treats up to 21 liters of coolant capacity.

Permatex 30301 Radiator Repair - Stop Leak, 16 fl oz, Protecting Against Coolant Loss, Stopping Leaks and Seepage from Head Gaskets

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Why We Love It

Reliable and cost-effective solution.
Premium formula stops leaks.
Easy and quick application.

Main Highlights

Reliable and Cost Effective: Designed to Provide Automotive Users with a Reliable and Cost-Effective Solution for Fixing Leaks in Your Cars Radiator System Without Clogging Radiator Cores.
Premium Formula: This Advanced Formula Protects Against Coolant Loss By Stopping Most Leaks from the Radiator, Heater Core and Engine Block Core Expansion Plugs As Well As Seepage from Head Gaskets.
Easy-To-Use: Easy to Use and Does Not Require Any Special Tools or Equipment, Making it An Quick and Easy Option to Fix Radiator Leaks On Your Own.
Peace of Mind: With Permatex Radiator - Stop Leak, You Can Drive With The Peace of Mind Knowing That Your Engine is Protected, and Your Car is Running Smoothly.

LavaTap – Fernox F4 Express Leak Sealer 400ml - Central Heating Leak Sealer Spray for Radiator and Pipe Leak Repair, Stop Leak Solution for Sealed Systems

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Why We Love It

Quick and easy application.
Safe for all heating systems.
Effective for hard-to-reach leaks.

Main Highlights

30-Second Application: Applies in just 30 seconds with no system drain-down required, helping you quickly seal leaks and restore pressure with minimal disruption.
Safe for All Heating Components: This radiator leak sealant is non-toxic and safe for boilers, pumps, air vents, and heat exchangers. Won’t cause blockages, making it ideal for sealed and combi systems.
High System Coverage: One 400ml can treats up to 130 litres—around 16 radiators or 250m² of underfloor heating—providing wide coverage for minor leaks in sealed systems.
Radiator Stop Leak Performance: Seeks out inaccessible micro-leaks caused by air ingress and seals them without blocking heat exchangers or pumps—ideal as a radiator stop leak for central heating systems.
Low-Impact Leak Sealant Spray: Powered by compressed air instead of harmful propellants, this leak sealant spray is non-flammable and comes in a fully recyclable can.
For Trade or DIY Maintenance: Trusted by heating engineers and DIY users alike, this leak sealer makes in-system leak repair quick and hassle-free—ideal for maintaining pressure in sealed systems.

CosWarm CW4 Central Heating Leak Sealer - Treats Up to 18 Radiators - Stops Leak - Boiler Leak Repair & Sealant - Stops Minor Leaks & Weeps, Fixes Pressure Loss & Leaking Pipes - Underfloor Heating

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Why We Love It

Seals leaks, saves time.
Protects metals, safe for environment.
Easy application, convenient usage.

Main Highlights

STOPS SMALL LEAKS & FIXES PRESSURE LOSS: CW4 Leak Sealer seals all the small and inaccessible leaks, thus saving time and money in draining down and repairing cost. Our boiler leak sealant also helps in fixing pressure loss due to minor leaks from central heating systems.
SUPER CONCENTRATED FORMULA: Our boiler and central heating system leak stopper can treat up to 18 single radiators, i.e., a 150-litre system. It is easy to use, just pour it in the system according to the instructions and let it work.
HARMLESS FOR METALS: There are many leak sealant chemicals that are not friendly when they come into contact with metals. CW4 Leak Sealer liquid is suitable for use with all the metals and materials, including steel, ferrous metals, copper and aluminium.
CONVENIENCE AT ITS BEST: Our leak sealer and stopper makes minor repairs in the boiler a breeze. It does not interfere with the working of your central heating systems and you won’t have to shut down the systems before or while using it. The product can be left in the system permanently.
SAFE FOR YOU, THE BOILERS & THE ENVIRONMENT: Our non-toxic radiator leak sealer is a safer alternative compared to other toxic, chemical formulas. As it is biodegradable, it won’t harm Mother Nature either. Safe to use around people, the environment and your heating systems.

K-Seal Coolant Leak, 236ml | Multi-use Car Radiator & Head Gasket Repair Sealant

5% OffFree Shipping

Why We Love It

No messy flushing required.
Easy and permanent solution.
Compatible with any antifreeze.

Main Highlights

FIX IT FAST: Our multi-purpose solution works in minutes to quickly & permanently seal leaks in the radiator, head gasket, freeze plugs, block, heater matrix & water pump. Fixes most leaks in water-cooled engines.
STOP HOLES & CRACKS: With just 1 step our unique formula will seek out each hole & crack, permanently sealing them, without any adverse impact on the efficiency of your engine cooling.
EASY TO USE: K-Seal couldn't be simpler to use & requires no draining or flushing; just shake, pour & go - shake the bottle, add the fluid to your coolant system & run your engine as normal.
VERSATILE COMPATIBILITY: Compatible with all types of antifreeze coolant. Suitable for use in both cars & light trucks with up to 12 cylinders. A permanent repair for the lifetime of the engine.
PROFESSIONAL-GRADE RELIABILITY: Trusted by mechanics, our sealer delivers a durable & long-lasting repair. A cost-effective solution to engine coolant leaks, enhancing the reliability & performance of your vehicle’s cooling system. We've sold millions worldwide & are independently verified by university testing to meet ASTM D3147.

Car Radiator & Hose Stop Leak Repair Additive Anti Corrosion 250ml Repairs Weld Cooling System Rads

Why We Love It

Permanently seals radiator leaks.
Works with anti-freeze.
Contains rust inhibitors.

Main Highlights

Permanently seals radiator leaks radweld k seal
Unaffected by anti-freeze
Contains rust inhibitors
Stops leaks in radiators and hoses
WILL BE SEND OUT SAME WORKING DAY IF ORDER PLACED BEFORE 2PM. YOU WILL RECEIVE IT NEXT WORKING DAY

Pro Line Radiator Stop Leak Coolant System Sealant 250ml

Why We Love It

Permanently seals small leaks.
Safe for aluminum radiators.
Compatible with all coolants.

Main Highlights

Permanently and reliably seals hairline cracks and small leaks
Suitable for aluminum radiators
For preventive use
No negative side effects on the water pump or heating circuit
Compatible with conventional coolants and antifreezes

Holts Radweld Plus Coolant Leak Repair, Total Coolant Leak Repair, Industry Leading Car Radiator Leak Sealant, Easy To Use, Seal Engine Block, Cylinder Head, Hoses & More, Suitable For All Cars, 250ml

16% OffFree Shipping

Why We Love It

Saves money on repairs.
Repairs leaks in minutes.
Anti-corrosion formula included.

Main Highlights

PROFESSIONAL COOLANT LEAK REPAIR : Radweld Plus is the total coolant leak repair, specially designed with an anti-corrosion formula that protects and maintains a healthy coolant system whilst eliminating the need to drain the system.
COMPLETE COOLANT LEAK REPAIR : Radweld Plus is the total coolant leak repair, specially designed with an anti-corrosion formula that protects and maintains a healthy coolant system whilst eliminating the need to drain the system.
AVOID COSTLY REPAIRS: With the rising cost of car replacement parts, save yourself the money and hassle of taking your car to the garage with Radweld Radiator Leak Repair. We have used our technical know-how to save you time and money.
EASY TO USE COOLANT REPAIR: It couldn’t be easier to repair your coolant leak with Radweld Plus - all you need to do is pour it in and let it locate and seal the leaks. It seals in minutes, with no clogging or damaging effects.
OVER 100 YEARS OF EXCELLENCE: At Holts, we have spent over a century offering solutions to your car troubles to make your life easier and stress free. If you want the perfect tools to maintain, repair or clean your vehicle, we have what you need.

LIQUI MOLY Pro-Line Radiator Stop Leak K | 250 ml | Cooler additive | SKU: 5178, red

50% OffFree Shipping

Why We Love It

Suitable for all systems.
Effective for small leaks.
Treats up to 40 liters.

Main Highlights

Suitable for all cold water and hot water systems, with or without water filters Also suitable for aluminium and plastic radiators. Cold water.
250 ml of paste is sufficient for 40 litres
Compatible with all standard cooling stabilisers and frost protection agents. Also suitable for preventative use.
For professional users only.
Small leaks caused by stone impacts, porous soldering points and hairline cracks in the cooling simple are easy to localize (one notices that the cooling water level is sinking).
Used for sealing small leaks in cooling circuits of passenger motor vehicles, commercial vehicles and buses. Also suited for cooling water circuits equipped with water filters.
Shake container before use. Start up the heater. With the engine running, pour the contents into the coolant at operating temperature and allow the engine to continue running for at least a further 10 minutes.
Contents will treat up to 40 liters of coolant.

8.7

Excellent

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We scanned 1210 products

We reviewed these offers relevant to the Radiator Sealant Leak Preventer within online retailers such as Amazon, eBay and other local retailers, ensuring we covered all major brands and models. The products we selected come from trusted brands like K-Seal, HOCHSTE, Permatex, LavaTap, CosWarm, Generic, Holts, Liqui Moly, all of which have a reputation for consistently delivering high-quality products that users love and innovative approaches for function & design.

For the best Radiator Sealant Leak Preventer in the market, we considered we took a deep dive into 6051 online reviews , focusing on elements like user satisfaction, performance in real-world conditions, and long-term reliability. Our ranking also evaluates each review’s relevancy, authenticity, up-to-dateness and depth so that the comparison is more sound.

We concluded that:

The clear winner of our analysis is K-Seal HD Coolant Leak Repair, 472ml | HGV Radiator, Block & Head Gasket Sealant. We love many things about this product by K-Seal. What sets it apart from the competition is No flushing required, simple, Multi-purpose and permanent solution, Compatible with all antifreeze.
The best value product for most shoppers and where user satisfaction is continuously the highest is Holts SEALit Leak Repair 250ml - Professional Radiator & Coolant Leak Sealer for Engine, Cylinder Head, Head Gasket, Freeze Plugs, Water Pump Gaskets, Radiators Red - 1 Pack 250ml by HOCHSTE based on online reviews by bloggers, experts and online shoppers.
The biggest bargain at the moment for Radiator Sealant Leak Preventer and the best cost-to-value ratio is LIQUI MOLY Pro-Line Radiator Stop Leak K | 250 ml | Cooler additive | SKU: 5178, redat Liqui Moly with a 50% discount.
Our list of the best Radiator Sealant Leak Preventer is updated regularly to reflect new releases and changes in product availability, so be sure to check back often for the latest rankings and discounts.

10 Best Radiator Sealant Leak Preventer in The UK

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We scanned 1210 products

We concluded that: