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

K-Seal is a lifesaver! I had a persistent coolant leak, and this product sealed it up quickly—no draining or flushing required. Just shake, pour, and drive! Within minutes, the leak was gone, and my engine's cooling efficiency remained intact.I love its versatility—it works with all types of antifreeze and is suitable for various engines, including light trucks and cars with up to 12 cylinders. The fact that it's backed by professional-grade testing and trusted by mechanics gives me confidence in its durability.If you’re looking for a simple, cost-effective solution to coolant leaks, this is it! Highly recommend keeping a bottle on hand for emergency repairs.

Really worked. 1989 Chevy K1500. Started spewing white, wet smoke. Somehow it sprang an internal coolant leak. Got the heads tested and they were okay. So presume it had to be engine block. However did not have leak until I changed the intake manifold gaskets. Thinking I messed up I did it twice, but still had a leak.This sealer really worked. Took 2 days of running and over night cooling to work, but after that ran fine. I als spend the big bucks on Blue Devil and it did not work.

Kseal once again probably the best leak stopper there is. and it just works. Plus they stand behind there products.

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!

It actually worked, no loss of coolant since I poured this tiny bottle of K-Seal into my truck. I am happy it wasn't my hose as this would not have fixed that. Also replacing the hose is very costly! This saved me a lot of money and anxiety.

Stops leaks quickly. This was recommended by a repair shop and boy does it work with out causing other issues.

very small

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.