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K-Seal ST5516 Heavy-Duty Multi-Purpose One Step Permanent Coolant Leak Repair, 8oz, Pour and Go, Mixes with All Antifreeze, No Flushing Required

4.3 4.3 out of 5 stars 1,278 ratings

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Purchase options and add-ons

  • Permanent Coolant Leak Repair: K-Seal’s unique formula will seek out holes and cracks, and permanently seal them, with no adverse impact on the efficiency of your engine cooling.
  • Versatile Usage: Fixes cracks and leaks in the radiator, head gasket, freeze plugs, cylinder heads, heater core, water pump casing and engine blocks
  • Heavy-Duty Universal Solution: This coolant stop leak was designed specifically for HGVs, tractors, heavy plant and other commercial vehicles. It can be used with all types of antifreeze
  • No Draining or Flushing: K-Seal coolant leak repair is easy to use. It eliminates the need for draining or flushing, making it a convenient solution. Just shake, pour and go.
  • Effective Cooling: The K-Seal 16 fluid ounce bottle is effective up to 40 quarts of cooling capacity
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K-Seal ST5516 Heavy-Duty Multi-Purpose One Step Permanent Coolant Leak Repair, 8oz, Pour and Go, Mixes with All Antifreeze, No Flushing Required
K-Seal ST5516 Heavy-Duty Multi-Purpose One Step Permanent Coolant Leak Repair, 8oz, Pour and Go, Mixes with All Antifreeze, No Flushing Required
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Price$20.96$139.99$247.00$15.49-13% $7.41
Typical:$8.48
$14.99
Delivery
Get it as soon as Sunday, Mar 31
Get it Mar 28 - 29
Get it Mar 29 - Apr 2
Get it as soon as Sunday, Mar 31
Get it as soon as Sunday, Mar 31
Customer Ratings
Easy to use
4.5
4.8
4.6
4.7
Mileage
3.8
3.8
4.1
4.6
Value for money
4.1
4.2
4.5
Sold By
Amazon.com
Denco Distributing Inc.
Craigsparts
R/A Hoerr Incorporated
Amazon.com
Amazon.com

From the manufacturer

kseal main
radiator stop leak

K-SEAL Coolant Leak Repair ST5516 Heavy Duty 16oz, Multi-Purpose Formula

radiator stop leak
The Safe and Easy Way to Fix a Coolant Leak

The secret behind K-Seal’s ability to repair a coolant leak is down to its contents: a specially developed blend of chemical ingredients including ceramic microfibers and copper particles. When added to the cooling system the ingredients disperse and flow freely around the system suspended in the coolant. If coolant is leaking from the system, either externally or internally across the head to the cylinders, then K-Seal will follow it through the hole or crack and try to fix the leak.

Permanent Coolant Leak Repair with K-Seal

Just Pour & Go

Coolant leaks don’t have to result in costly repair bills – simply add K-Seal to your coolant system for a quick and permanent fix. K-Seal is trusted by millions of customers worldwide, and the only coolant leak repair fluid carried by the AA, the UK’s largest roadside repair company.

K-Seal’s unique formula will seek out holes and cracks, and permanently seal them, with no adverse impact on the efficiency of your engine cooling.

  • Fixes most leaks in water-cooled engines
  • Repair for the lifetime of the engine
5516
radiator stop leak

Coolant System Sealer

Just Pour & Go

Once the crack or hole has been located, the microfibers instantly begin to mesh together within the gap, building a seal literally fiber by fiber to stop the coolant leaking through the gap.

The particles in our K-Seal products are very precisely designed to be large enough to repair holes up to 0.635mm in size but deliberately small enough to never block any passageways or tubes within the cooling system, including those inside the heater core and radiator.

Once the microfibers have sealed and fixed the leak, a combination of exposure to either the external atmosphere or the gases within the combustion chamber and the heat within the cooling system and engine causes the K-Seal formula to cure. This results in an extremely strong and permanent seal able to withstand even the high pressures from the combustion chamber. K-Seal Ultimate is able to repair head gasket failures, even where the cooling system is being over-pressurised by exhaust gases entering the system.

Common Coolant Leaks

K-Seal can deal with all of these leaks and more, as long as they are identified as early as possible. It is easy to use – simply shake it and pour it into the coolant mixture and it will work automatically.

Types of leaks that can occur within your car’s engine

  • Head gasket leak, where the coolant is allowed to enter the engine cylinder
  • Engine block leak, where the stressed metal cracks and leaks coolant
  • Water pump leak, where leaks develop under stress or abrasion and coolant leaks out
  • Radiator leak, where circulating coolant leaks and causes the engine to overheat
K-Seal Permanent Coolant Leak Repair

Product Description

Experience the ultimate solution to coolant leaks with the K-Seal ST5516 HD, a multi-purpose, one-step permanent coolant leak repair. Our powerful formula works seamlessly with all antifreeze, making it a universal fit type for all your needs. No need for draining or flushing your system. This heavy-duty sealer was designed specifically for HGVs, tractors, heavy plant and other commercial vehicles. The K-Seal ST5516 HD, also known as a head gasket stop leak, works by sealing leaks efficiently and permanently. It also doubles as a radiator stop leak, effectively putting an end to any leaks in your radiator. The permanent leak sealer is easy to use - just shake, pour, and go. This product excels in fixing cracks and leaks in several components including the radiator, head gasket, freeze plugs, cylinder heads, heater core, water pump casing, and engine blocks. With a single 8 fluid ounce bottle of our coolant leak sealer, you can treat up to 20 quarts cooling capacity. This heavy duty stop leak sealant is a must-have for all your coolant leak issues. So, forget your coolant leak worries with the K-Seal ST5516 HD. Experience the power of a seal stop leak that stops leaks permanently, offering peace of mind and extended life for your vehicle's cooling system. Trust the K-Seal coolant leak repair for a lasting solution to all your coolant leak problems.

Product information

Technical Details

Additional Information

Warranty & Support

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K-Seal

K-Seal ST5516 Heavy-Duty Multi-Purpose One Step Permanent Coolant Leak Repair, 8oz, Pour and Go, Mixes with All Antifreeze, No Flushing Required


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What's in the box

  • K-Seal ST5516 HD Multi Purpose One Step Permanent Coolant Leak Repair
  • Product guides and documents

    Looking for specific info?

    Customer reviews

    4.3 out of 5 stars
    4.3 out of 5
    1,278 global ratings

    Customers say

    Customers like the value, ease of use, and speed of the auto accessory. For example, they mention it's well worth the money, easy to use, works fast, and saves them thousands of dollars. That said, opinions are mixed on performance, leakage, heating, and smoke.

    AI-generated from the text of customer reviews

    37 customers mention26 positive11 negative

    Customers like the value of the auto accessory. They say it's well worth the money, saved them thousands of dollars, and is a great buy. It's also cheaper than replacing their engine block.

    "...This is the best stuff I've found. Not only is the price good but this product doesn't clog your system up. And you can just pour and ride away." Read more

    "...how well it will seal, but for a stopgap measure it's certainly well worth the money." Read more

    "...It does not seal. Still overheats. Tried it. All advertising, no substance." Read more

    "...Product Is Fairly Priced, Easy To Use. EGR Coolers On Trucks Lifespan Average Just Under 100,000 Miles." Read more

    12 customers mention12 positive0 negative

    Customers find the auto accessory easy to use. They say it does a great job of sealing and works every time.

    "...It sealed the leak and has stayed sealed for several months now. Easy to use. Just poured it into the reservoir and I was done! Top notch product!" Read more

    "Ease of use. Works Quick as described. No more radiator leak. 1961 Farmall 460 tractor ;)" Read more

    "easy to use.... I used for my gm 3800 timing cover coolant leak, was worth a try at least...." Read more

    "...Product Is Fairly Priced, Easy To Use. EGR Coolers On Trucks Lifespan Average Just Under 100,000 Miles." Read more

    11 customers mention11 positive0 negative

    Customers are satisfied with the speed of the auto accessory. They mention that it works great on their vehicle in minutes and solves their problem right away. Some customers also appreciate the fast shipping.

    "Ease of use. Works Quick as described. No more radiator leak. 1961 Farmall 460 tractor ;)" Read more

    "The product works super fast, in less than one minute the leaking water pump stopped and after one long month the leaking still never comes back." Read more

    "It worked, and it worked FAST! I am skeptical of it's long-term reliability, but I only used to to plug a leak long enough to sell the car anyways...." Read more

    "This product worked perfectly and immediately. My 2003 Yukon had been leaking a little or a lot daily for several months...." Read more

    96 customers mention51 positive45 negative

    Customers are mixed about the leakage of the auto accessory. Some mention that it works first time and stops the leak, while others say that it started leaking again about a day after they put it in. Some customers also mention that the product is easy to use and has stayed sealed for several months. However, some customers report that the leak from the EGR cooler, intake manifold gasket, and valve cover gasket still occurs.

    "...Worked first time, no more leaking into the engine oil of coolant.Now after 2 months leak still gone... Amazing" Read more

    "My transmission was Leaking and that fixed it" Read more

    "...Sealed up the leak until we could get it serviced and allowed us to finish up the job we started. Thank you I definitely would recommend it to anyone" Read more

    "...And again for a third time, which I used a month ago. Not only it sealed the leak, again, not 100%, but good enough for the engine light to go off,..." Read more

    89 customers mention58 positive31 negative

    Customers are mixed about the performance of the auto accessory. Some mention that it worked great for them, is of quality, and can work well as a temporary fix. However, others say that it didn't work like they thought it would, stops working after a month or two, and has absolutely no effect on the problem.

    "...weekend and shops were closed had to come up with a quick fix and this works great!..." Read more

    "Didn’t work as a ounce" Read more

    "...Would I suggest to others to buy it? Not sure. It can work good as a temporary fix, but don't rely on it to do the perfect work." Read more

    "Excellent product, it stop a big leak in my forklift, it has been working without any problems" Read more

    12 customers mention5 positive7 negative

    Customers are mixed about the heating of the auto accessory. Some mention that it runs perfectly with no heating issues, while others say that it still overheats and emits lots of vapor from tailpipe.

    "Ranger Polaris Crew diesel engine made by Yanmar. Engine kept overheating-ENTIRE cooling system has been replaced $$$.EVERY PART BUT the engine...." Read more

    "...The car has stopped using coolant,very pleased with product and customer support. P.S. i don't do many reviews." Read more

    "...BUT , it only has 66k on it. I didn't do a diagnostic, but it was running hot, and there was boiling, and though I didn't see any coolant on the..." Read more

    "...My AC is blowing cooler as well. Whatever leaks I had have been sealed. $20 is a hell of a lot better than $6000 or having to buy a new vehicle." Read more

    10 customers mention4 positive6 negative

    Customers have mixed opinions about the smoke produced by the auto accessory. Some mention that their car has a small leak, but produces no white smoke from the exhausting pipe. Others say that their vehicle is blowing tons of white smoke during morning start or cold.

    "...would work, but lo and behold... check engine lights are off, white smoke stopped, and she’s running great...." Read more

    "...let the car sit for 3 or 4 days and upon start up there was a big puff of white smoke and I got the check engine light...." Read more

    "Simply put, it works. Stopped the white smoke and bellowing from exhaust in about 5 minutes, may not work for larger breaks in a head gasket but, it..." Read more

    "...and over the valve for cylinder 2, causing a misfire and a lot of smoke on cold starts...." Read more

    6 customers mention0 positive6 negative

    Customers are not satisfied with the auto accessory. They mention that it works great, but not for as long as expected. Some customers also report that the product stops the rediator, but it leaks.

    "This stuff worked great, but not for as long as expected. Other reviews said it lasted 6 months, but for me only 6 weeks...." Read more

    "...I tried this product and all I got was a stopped up petcock and fiberglass in my bottle and cap.Didn't stop the issue at hand...." Read more

    "...It really worked, normally this bandaid stuff is sham or very short term stop but it seems to be holding up." Read more

    "This K-Seal ST5516 HD was fine at the begining, but did not last that long as the 1st K-Seal stop leak product did." Read more

    K Seal did fix intake manifold gasket leak.
    5 Stars
    K Seal did fix intake manifold gasket leak.
    So I have a 2005 Chrysler Pacifica, with about 206,000 miles. For the last 2 years I've been fighting this leak through the intake manifold gasket, where I would have to put in about of quart of coolant every 3 days. I've been working on cars all my life so I know how hard it is to change a head gasket or even a intake manifold gasket. Throughout the two years I've been using J-B weld aluminum extreme heat which were only suppressed the leak for about 2 months at a time. After doing a little bit of research I came across this product. Started watching videos and reading testimonials. I was like what the heck let me try it. The leak would occur usually about three to five minutes after I start my car. I added a little bit more coolant, and started my car. I followed the instructions shaking the bottle for 30 seconds vigorously and proceeded to pour the whole bottle into the reservoir tank. My car was really low on coolant so when I added the k seal it went directly from the reservoir into the block. I added a little more coolant to top the reservoir tank off and and place the cap back on the reservoir. At this point my car had already been running for about 5 minutes and what do you know not a trace of coolant was leaking. Like I said before this been happening for 2 years so I know that the coolant should have been leaking by now. So I let the car run for 30 minutes. I turned on the heat full blast just so it wouldn't get clogged into the coils of the heater core. Usually about 30 minutes of running my car the coolant would have been pouring out of the gasket in between the intake manifold and the head. There was no leak at all. After close inspection the area was bone dry. I have never witnessed a product that can fit fix a gasket leak like this one. It literally save me about $1,500 in costly repairs, actually would have been less because I would have been fixing it myself ,but still save me about 5 to 8 hours of labor. So my review for this product is definitely 5 stars and it definitely worked in my situation. I will update this in about 30 days. See the video for yourself.UPDATE: As of today, (May 19th). the leak is still sealed. It's been about 45 days and the seal is still going strong!
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    Top reviews from the United States

    Reviewed in the United States on November 4, 2023
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    Reviewed in the United States on November 10, 2023
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    5.0 out of 5 stars Did wonders!! Works great
    Reviewed in the United States on November 10, 2023
    Had a leak on our tractor at work unfortunately it was pushing the weekend and shops were closed had to come up with a quick fix and this works great! Sealed up the leak until we could get it serviced and allowed us to finish up the job we started. Thank you I definitely would recommend it to anyone
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    Reviewed in the United States on May 31, 2023
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    Reviewed in the United States on January 4, 2021
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    Top reviews from other countries

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    Dawg
    5.0 out of 5 stars This bar none the best stop leak
    Reviewed in Canada on December 18, 2023
    Alberto
    5.0 out of 5 stars Gran sellador
    Reviewed in Mexico on June 28, 2021
    Amazon Customer
    5.0 out of 5 stars It really worked and saved a lot of money
    Reviewed in India on June 25, 2018
    4 people found this helpful
    Report
    matt
    5.0 out of 5 stars Holding so far
    Reviewed in Canada on December 29, 2023
    Ravi
    5.0 out of 5 stars it works
    Reviewed in India on April 24, 2021