K-Seal ST5501 Multi-Purpose One Step Coolant Leak Repair, 8oz, Pour and Go, Mixes with All Antifreeze, No Flushing Required

This product is a life saver. The water pump of my car start to leak heavily, so I pour abottle of k-seal on the radiator and the leak was reduced at 97%. It gave the time to keep runing the car for a couple of weeks until I get the new water pump and installed. Obviously I check the radiator level daily but the product due his work compared to the scale of damage the water pump seal had.

I have a 2000 Pontiac Grand AM GT V6 3400 engine, bought the car new from the dealer. A few years back the engine developed a coolant leak in the lower intake manifold, discovered oil in the coolant and needed to fill the radiator tank every couple of weeks. I had a mechanic remove the intake and replace the gaskets; he also suggest I have the heads removed and new head gaskets installed while he had it apart. $1,500 later it was back together and running great, no more leaks. Fast forward about 10K miles and a little over a year later, out of warranty I may add, the engine would smell of coolant and started to leak externally. I was going through a gallon a coolant every couple weeks. Take into account this car has about 100K miles and has a market value of about $1,800. I wasn't going to throw anymore money after bad. So I kept driving it, but one morning I started it up cold and the engine began to miss on 1 or 2 cylinders, the check engine was flashing, indicated the misfiring cylinders. I towed it to another mechanic to see what the cause was, turns out the head gasket was blown this time, compression test proved his theory, he suggested I get another engine from a junked used car and try my luck. That would cost about $3,000 with parts and labor. Not about to throw any more money away, I had the car towed back to my house where it sat for a few months. Not sure what to do with this car, body, paint and interior was in excellent condition, oil was always changed with Mobile 1, it was a well maintained car, was a shame to see it there dead in the driveway. Just had new tires and brakes installed prior to the coolant leak. One day I ran across an article promoting K-Seal, after reading the great reviews here on Amazon, I figured what the heck. It was either call the junk yard and have them pick up the car or spend less than the cost of lunch and give it a shot. Can't believe how easy it was to do, I pulled the radiator hose from the engine block, poured in the K-Seal and reinstalled the hose. The directions state you do not have to drain the coolant like other brands require. Started the car up, and of course the engine was misfiring and check engine light began to flash like before. I let it idle for a few minutes to warm up, when it got to operating temperature, I took it for a drive around the neighborhood. Within about a mile of driving, the engine smoothed out and the CE light went dark. Drove around for another 20 minutes and returned home. I parked the car and check underneath to see if the coolant was leaking like before, to my surprise it had stopped! I let the engine cool and topped off the coolant reservoir with fresh antifreeze until full. I decide to drive the car to work the next day, a 35 miles commute one way into the city, in the middle of summer, ran flawless. Wow! Absolutely no problems since the K-Seal treatment. I have been driving the car now for 7 months and about 6K miles. The coolant hasn't leak a bit and the car runs flawless.Even my mechanic can't believe this stuff actually worked. I am a believer and have since told many people of my experience with this product. Had a buddy with a similar issue with his beloved 2 DR Accord V6, fixed his leak too! I normally don't spend the time to write reviews, but this product truly has made a believer out of me. What do you have to lose? I almost threw away my car, and for a measly few dollars it is now back on the road better than ever. Thank you K-Seal ! I want to add that after reading the one star reviews on this forum that these people were not using the product as intended. It is designed to very small leaks like in gaskets and cracks in the engine block of heads. It needs high heat to cure the fine copper powder that forms a new gasket. If you have a large leak in a radiator, heater core or hose, it's probably not going to work for very long if at all, better off replacing them. Now head gaskets, yes give it a shot! UPDATE: 9/9/16 Still no leaks, I've clocked 20K+ miles on K-Seal with no issues. Hoping for another 20K... buy this stuff. UPDATE: 1/11/17 Well, the engine miss has returned, anti-freeze is disappearing again, head gasket is leaking again. Just poured another bottle of K-Seal in again, within 5 minutes the leak is repaired again. This stuff is great, my old beater is good for another 20K I hope. Money saved again! My mileage on the first repair was 23K miles, not bad for a $11 fix.

Tried this after a good couple of years of dealing with a chronic overheating issue in my Saturn Aura. Considering that the repair cost at a garage would be well over the current value of the car I basically dumped distilled water and coolant into the reservoir whenever it started getting hot. I noticed a strong coolant smell every time the thermostat started fluctuating on the dash. So I decided to try this stuff recently. I noticed the difference on a grocery run; aside from the lack of overheating issues, the lack of the coolant smell when parked and the fans going on at full blast! A few trips to the store later the repair seems to have held up, the heater is working normally again, no wild fluctuating thermostat. It may be a temporary repair but if it lasts a few months or forever it's worth a try if you have this issue with your vehicle. UPDATE: 8 months later it still holds up. UPDATE #2: Leak returned. Attempted to fix with this again and does not seem to work. Again, good for temporary repair, it held up for over a year, depends on how severe the hole in the system is I suppose?

I am always reluctant to use these kind of products but I thought " hey, it's 2023, automotive chemistry advanced since stop leak fluids used to clog heater cores and water pumps". My issue with the car was a small pinhole leak in the heater core. Since taking apart the dashboard didn't sound fun, against the advice of all my friends, I've decided to use K-Seal. I used it just as it was recommended, turn heat to ON and drove it 20 miles each way. The putrid smell of coolant slowly dissipated inside the vehicle, hence I knew it's working. Second day, I took the car on a short run and guess what? Overheating. Noooooo. Impossible. Stop leak products never do that...well I did some Google searches...yes, they do that occasionally. I think right now the stop seal product clogged the thermostat. The car is good for about 4-5 miles then it starts overheating. I called the K-Seal customer service and a lady answered immediately ( by that I mean after second ring, no wait, no "press 1 for product help"). I told her the story and she said " it's very strange, never happens". Hmm..really? She advised to flush the system and take it from there. I just hope to Jesus, the radiator passages are not clogged. So, I'll give it two stars because I believe that the product did seal the pinhole in the heater core. Unfortunately, it sealed other parts of the cooling system that didn't need sealing, such as ( best case scenario) the thermostat. December 18 follow up. At the advice of KSeal customer service and because the car was overheating, I've dumped the coolant and KSeal and flushed the whole system. I flushed with distilled water and even drove it for 20 min. As soon as I dumped the KSeal, the car started working normally. No more overheating. I dumped the the distilled water and filled with 50/50 generic coolant. No more issues with overheating....but heater core is leaking...again. So in conclusion, I wouldn't bother with this. Like many others said...fix the issue don't bother with K seal. Best case scenario, you can buy time. My case? Not that it didn't even work...it overheated my car and had to spend extra time and money to flush the system to get it out. December 28 Follow Up. So, a few days before Christmas, I called the company again and the same nice lady answered immediately. I told her I flushed the system and now leaks came back with vengeance. She was still at a loss for words but said she will send another bottle for free. In the meantime, I thought about it long and hard, went back to the website and read directions again. I also realized that when I added K The first time, as per instructions, I added to expansion tank. Expansion tank had plenty coolant in it...but the radiator did not. Because my radiator cap was slowly falling apart, the system wasn't pressurizing properly and coolant wasn't really being drawn into the radiator. I was driving with 50% coolant and K Seal couldn't do it's job since not much was taken from the expansion tank. Yesterday, December 27, the second bottle of K Seal arrived. This time, I got my magic funnel which burps the system and in a coolant jug, I mixed the K Seal along with 50-50 coolant. Turned the engine on, funnel attached/installed on the radiator and heat inside the car, to maximum hot. I would like to mention that at this point, most of the coolant from the radiator was leaked out. The car slowly started taking the mixture in and burping air. After about 10 min, the air was not too hot out of the vents, but the fan was on. I went inside the car and gave it a bit of gas. With a big burp of air, more coolant went in and air become super hot in the cab. I kept the engine running with the heat on for about 40 minutes overall. I turned the engine off, took down the funnel and attachments and installed my new radiator cap. Ran the engine again for about 20 min this time to pressurize the leak. Two hours later, I took the cap off and fluid was right at the neck where it should be. Next day, the same thing. I am 98% sure that the leak was fixed. Will check again in a few days. My advice is to add K Seal directly to the radiator if possible. If you have a leak in the system, radiator should be low already. As per instructions, they don't want the K Seal to touch the metal inside the radiator directly so I would mix it in a smaller bottle with some coolant premix or distilled water and then add that directly in the radiator. I would strongly advise using a burping funnel because of air gets into the system, K seal won't work properly. April 2004 update. Heater core started to leak again. K Seal does give you enough time to get to the mechanic though but I would just use it for that. Not as a permanent solution. I bought a heater delete kit and finally took care of the problem. Two weeks later car started to overheat slightly in turn affecting the AC operation. Fluid level seemed ok but coolant was boiling over. Bought a new thermostat and replaced the old one. Did the K Seal clogged it? I don't know, but thermostat was about 7-8 years old and wasn't OEM. Would I use ANY stop leak again? Only if I am broken down on the side of the road.

I had a little pin hole leak in my radiator on my 2002 VW Passat wagon (130k miles). It was somewhere in the fins so it wasn't something I could do a JB weld fix on. While i was contemplating spending the six hundred bucks in [parts and labor to replace the radiator, i just kept adding more coolant. It wasn't a really bad leak. Mostly just annoying because of the smell of burning radiator fluid. But after about a week, it just stopped leaking on it's own, so I've been driving around town with my fingers crossed hoping it would not start leaking again. But then we had planned a family trip out to New Mexico from KC. It was about 110 degrees F out and 1,400 miles to cover round trip with very long stretches of highway cutting thought the middle of nowhere, with absolutely nothing around for miles, so the idea that the radiator would probably choose this time to start leaking again was a serious concern to me. Yes, technically I should have just replaced the radiator, but instead i decided to just bring a couple of gallons of pre-mixed coolant along and ordered a bottle of K-Seal to take along as a "just in case" precaution. Sure enough about half way out there the radiator started to leak again. This time worse than before. So i carefully followed the directions, shaking the bottle of K-Seal but poured only about half of the bottle into the reservoir/overflow tank (the bottle said it would treat up to 10 cylinders and worked on cracked cylinder heads and engine blocks, so i figured half a bottle would be plenty for a little radiator pinhole) As other reviewers have observed it does come out as a thickish ugly brown liquid that just sits there in the bottom of your overflow tank. Which is admittedly kind of scary, especially if you are skeptical of these products to begin with. But shortly after the car was up to temperature, the leak stopped, as advertised -- even though the k-seal was still very noticeably sitting at the bottom of the overflow tank. VW antifreeze is reddish pink and the K-seal at the bottom was a darker brown. After driving the rest of the way out there it had mixed with the rest of the coolant so it didn't look as nasty in the tank. I've driven another 1600 miles on it and not had any issues. I think the biggest fear with these types of "sealer" products is not that they will not actually seal the leak, but that they will gum up all the intricate little passageways in your heater core, and the rest of your cooling system, but I haven't had any issues at all with this. If I do, I'll be sure to post back and downgrade my 5-star rating. So, I'm sold. this stuff saved my butt and I would definitely recommend it -- especially if you're in a bind. I would never use this (or any other product like this) as a preventative measure like some of the product testimonials on the K-Seal web site, but if you have an older car that you don't want to dump a bunch of money in for repairs, I'd definitely give this a go.

I have a 25 year old Nissan Pathfinder SUV with over 180000 miles that still runs like it did when I drove it off the dealer lot. Last year, it developed a small coolant leak at a connection to a coolant line between the engine and the firewall. The only way to find it was with a coolant system pressure tester. Getting to that connection to replace the hose requires taking off almost everything above the cylinder heads on the engine--many thousands of dollars if I paid a mechanic, days of difficult work for me, or time to sell for most people. I really didn't have anything to lose giving this stuff a try. And it worked! It stopped the leak with no discernable affect on my cooling system or engine. I am writing this review one year later, and the leak is still sealed. No loss of coolant since, and the engine runs at the same operating temp as it always has. Thank you K-Seal!

Didn't fix my leak

To start, this is gonna be a long review aimed at helping others understand how I used this product successfully, so prepare for the long haul... TLDR, K-Seal does actually work, but you need to be careful in applying it based on my experience so far. I bought this product on Amazon in an act of desperation. I had purchased an old first generation Hyundai Santa Fe last year that suffered numerous, expensive breakdowns. After paying thousands of dollars in various repairs, the dreaded sweet smelling white clouds of smoke started pouring out of my tailpipe in October. No leaks on the ground, but there was white smoke coming out the tailpipe and around the base of the engine, so the issue became quite severe very quickly. One important point, my vehicle has never overheated... if it had, I am not sure if this product would have worked. I do not think I warped the head, I believe the gasket just blew. This happened right after putting in a brand new radiator, which has had no leaks. I was losing a few ounces every 20 miles or so. This was an awful predicament as a proper head gasket replacement was estimated over $4K, which was a bit more than what I had paid for multiple repairs to date. Point is, I was desperate and started looking through all the stop leak products for the one least likely to damage my vehicle. This was a roll of the dice, and I think it is important to say that the best way to ensure your vehicle lasts is to replace the failing parts properly. You never-ever want to put sealant products into your engine or transmission unless you are truly desperate due to prohibitive cost to repair properly. But here I was, owning a vehicle that wasn't worth what I had already paid into it for repairs with a massive failure looming... so I bought this. Not to speak poorly of other products, which also are reviewed on Amazon with varying levels of success, but I liked that this product did not contain "liquid glass", which is a chemical that hardens up solid in the coolant system. Mind you, if applied properly, those might be an even better product than this one in the long term, but I read many customer reviews where those products could solidify in the wrong spot like the thermostat or radiator, totalling the engine shortly after. This product seemed the least harmful due to the way it is advertised as using small particles to stop leaks. But make no mistake, this stuff clumps up by design and can definitely cause clogs in the wrong place. So, here is my K-Seal experience, please take it with a grain of salt as I am not responsible if this approach damages your vehicle. If you read the instructions on the bottle, it says to pour all of the bottle directly into the overflow coolant tank or directly into the engine block via an open coolant hose. I was super anxious about pouring that much in as the bottle states that this treats up to 22 liters of coolant... my vehicle has a little over 7 liters in it! I give credit to an earlier reviewer who recommended using less of the product incrementally, I absolutely used that approach. The key is patience (a LOT of patience!). I took a clean 4 ounce mini-water bottle and thoroughly mixed 2 ounces of this product with 2 ounces of coolant for a couple of minutes. Product will be a glittery copper color when combined. Then I poured it into my coolant overflow tank (make sure not to overfill, this product will very likely cause coolant in overflow tank to increase) and idled the vehicle. The instructions indicated 15 minutes or so should be enough, but I ran it for an hour. I was watching the tailpipe and did not really see a decrease in smoke so was disappointed, but recognized that this product works by getting very hot, circulating towards holes/gaps, gradually "clots" where an atmosphere is present, and semi-solidifies. So I shut down the vehicle for 48 hours to allow the product to solidify. Then I checked the coolant level, which was still elevated from the prior treatment and used the SUV. To my disappointment, over the next hundred miles, the coolant level continued to drop. So roughly 10 days later, I repeated the process and gave the product time to harden. The next time I ran the vehicle I became alarmed, the engine made a low groaning sound for the first few minutes... I think the product may have gummed something up but thankfully it cleared up after five minutes. I drove the vehicle for about around 50 miles but still saw and smelled the white smoke everywhere. I let it sit a few days, drove it with little improvement for 2 weeks, then applied one more treatment. I used about 6 ounces of the product in total. Then I decided to just drive it around and see if repeated cycles over time helped... and it did. Verrrryy gradually. I still have some white smoke coming out of the tailpipe today, but much less than before and my coolant level is stable. I would call this a success, and am keeping the last 2 ounces premixed in my trunk just In case it fails down the line. To cap my long story, it has been roughly 4 months since I went through these trials with this product. I only drive short distances locally and have put 330 miles on the car since putting this stuff in, and it is performing well. No overheating (which I am constantly watching for - you should too if using this or any sealant products in case the thermostat gets sealed). In sum, $14 saved me $4000+ on a vehicle that is not worth the additional cost. It was worth taking the chance for me as it is a high mileage old SUV. If it was a new car, I would very likely consider getting the head gasket repaired properly, but would keep this as a viable backup option if desperate and willing to chance destroying the engine if it fails. This is one of those products that is worth keeping in the trunk for emergency use. I will provide updates here if the product suddenly fails or at the beginning every year I own the SUV so you will know the long term use case for K-Seal. Thanks for reading and best of luck all! Update: 12/7/2022 - Well, this miracle in a bottle has failed just over a year after I put it in, roughly 1500 miles later. I heard bubbling in the front of the SUV dashboard earlier this week, which indicates that air is getting into the heater core. No visible bubbling in the coolant overflow tank and no "chocolate milk" in the oil from coolant mixing in, which is good. I checked the tailpipe and saw the white sweet smelling smoke coming out steadily. I purged the air from the system and added the last 2 ounces of K-Seal to the coolant system, hopefully it works like it did before. Given that I drive this SUV quite frequently for short local trips (2-6 miles at a time), this chemical did a great job sealing the leak for a prolonged period. It may not be a permanent fix in my case, but I have no issue adding more K-Seal periodically if it reseals the head gasket without damaging the engine or other cooling system parts. It's still a huge cost savings compared to a proper head gasket replacement's cost. I will provide an update once I have a chance to evaluate if the sealer works again or not. One other thing to mention that I did last year (but forgot to note in the original review)... I was very concerned that my working order heater core could get sealed off by this stuff, so I never ran the heater as the K-Seal instructions recommended. Instead, I set the temperature controls to the coldest setting and "off" mode to reduce the likelihood of K-Seal going through the heater core when applying it for the first few heating/cooldown cycles. I am not saying this is the correct thing to do, and if you try it, it's completely at your own risk, but... I had plenty of strong heat from the heater core all winter last year. I did the same thing this time around. Just food for thought for like-minded individuals who are also very concerned about applying sealers in the heater core. I think this method helped, but I could be wrong. In any event, I hope this update is helpful for those with similar head gasket issues. Update: 6.9.2024 - Vehicle is still running well using the approach I outlined above roughly 2,500 miles later. I noted minimal white smoke during the past winter but no large clouds of smoke nor any bubbling in the overflow reservoir; my heater was running nice and hot too. Since the prior update, I have not used any more K-Seal. I plan to only add an ounce or two if I observe symptoms of a worsening head gasket leak but will not add more than the second bottle in total per the K-Seal manufacturer instructions. This product will likely keep my old SUV running for a couple more years at this rate, which is pretty astounding. It literally saved my vehicle from catastrophic failure and cost me less than $35 in cost for two bottles overall. Hope it works for you all too, good luck! Update: 9.29.2025 - My vehicle is still running well another 1,000+ miles later. I did have an issue very recently with the K-seal sealant clogging my radiator cap, causing the coolant hose to pop right off the radiator due to back pressure and rapidly leak hot coolant out. The tell tale sign was white smoke and a sweet smell coming from under the hood. Luckily I was close to home and shut the vehicle down before it overheated. I cleaned out the many pieces of sealant sludge from the radiator cap with a needle and got back on the road soon after, no further issues. The head gasket seal is still holding, with minor white smoke appearing occasionally but no other performance issues. It's been over 4 years since I started using this product and my SUV is still running with no signs of serious head gasket leak damage. I couldn't be happier with the results from using K-seal.

Great product

Seems to stop leaking from plastic header of the radiator.

The best coolant leak repair product available!I have used it many times on leaking radiators and cracked engine blocks.Really good product,does the job every time.

merhaba aracımda 2-3 günde 50-60 km kullanım sonrasında 500 ml kadar ciddi bir su eksiltme problemi vardı 20 şubat günü ürünü kullanım talimatına uygun olarak yedek depo içinde full antifiriz varken kullandım ilk kullanım sonrası 250 ml kadar bir eksiltme yaptı üzerini max çizgisine kadar tekrar antifiriz ile tamamladım 45 gün kadar oldu her hangi bir eksiltme olmadı şu an için daha önce kulladığım bir çok üründen daha başarılı

Fungerade mycket bra. Jag är nöjd. Bara att skaka burke jättenoga först. Sen hel i allt