The 9 Best Radiator Stop Leaks

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This wiki has been updated 22 times since it was first published in April of 2018. When smoke billows from the engine bay, the temperature rises, and the air smells too sweet, the likely culprit is an antifreeze leak. Because they're exposed to the elements, radiators are often the first component to corrode, but one of these specially formulated sealers can stop your system from losing coolant until you can find a more permanent solution once you can drive to the shop. When users buy our independently chosen editorial selections, we may earn commissions to help fund the Wiki.

1. Bar's Leaks Concentrate

2. K-Seal ST5501

3. Liqui Moly 20132

Editor's Notes

February 12, 2021:

There haven't been any recent advances in radiator stop leak additives, so our recommendations remain the same. We do want to point out, though, that if you're not careful, this kind of additive could make some problems worse, by damaging other coolant system components like the water pump. That's not to say these don't work for some people, but rather, it's very important to exercise caution and follow the directions closely. Also, these are, more often than not, only temporary fixes, and should be followed up with actual repair before too long. If you find yourself using multiple stop leaks without success, or if your vehicle needs repeated additive uses, your best bet is to get it fixed in order to avoid long-term damage.

October 02, 2019:

Removed Irontite Ceramic because it is not meant to seal radiators. Its primary use is sealing head gaskets and engine blocks. Added Liqui Moly 20132 and BlueDevil 205. The BlueDevil is widely used and can be very effective for sealing cracks when an immediate visit to a mechanic's shop is not an option.

Many of these products claim to offer permanent leak solutions. While some of them may or may not seal leaks for long periods of time, they will never be an actual substitution for part replacement. Never rely on these products for long-term service - its best to get the leaking part replaced rather than risk getting stranded because the seal failed or the crack expanded. All of these products can work very well in the short term to prevent significant engine damage caused by overheating.

Opening a coolant system can be extremely dangerous and may result in severe burns. Always allow the engine to cool before attempting to remove the radiator cap or any other component. Working on engines is best left to trained automotive technicians to avoid personal injury or damage to equipment.

4. Bar's Leaks Tablets

5. BlueDevil 205

6. Blue Magic Liquid Glass

7. Bar's Leaks Liquid Aluminum

8. AlumaSeal ASBPI12

9. K-Seal HD

Christopher Thomas
Last updated by Christopher Thomas

Building PCs, remodeling, and cooking since he was young, quasi-renowned trumpeter Christopher Thomas traveled the USA performing at and organizing shows from an early age. His work experiences led him to open a catering company, eventually becoming a sous chef in several fine LA restaurants. He enjoys all sorts of barely necessary gadgets, specialty computing, cutting-edge video games, and modern social policy. He has given talks on debunking pseudoscience, the Dunning-Kruger effect, culinary technique, and traveling. After two decades of product and market research, Chris has a keen sense of what people want to know and how to explain it clearly. He delights in parsing complex subjects for anyone who will listen -- because teaching is the best way to ensure that you understand things yourself.

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