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

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!

So far its a great temporary fix. I used the K-Seal for my 2007 Honda Pilot EX-L 4WD. For clarification, after having my vehicle pressure tested, and radiator cooling system no leaks were found. But, when a CO2 test was performed to determine if cylinder head gaskets could be to blame for my coolant leak, the test revealed slight CO2 in cooling the system, resulting from possible head gasket failure. So, I'll need to replace head gaskets and recheck cooling system. In the meantime since using K-Seal, the coolant does not appear to be leaking from my radiator and my engine bay has remained clean of any backsplash. Other thing to be noted is that there is a slight difference in the heat coming off the engine as well. So, great value for money, and functionality appears to be working as intended.

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.

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!