20 Best Heater Core Leak Sealant (2023 Updated)

Imagine seeing smoke coming from under the hood only to pop it and see a pool of coolant on the ground. I’m just imagining spending more money (that I don’t have!) at the mechanic. This was referred to me by a friend who has a shop.

Half a bottle did the trick. No more leaking coolant.

I’ve been dealing w/ a minor head gasket leak for a couple years now on my ’03 Explorer 4. 6L. Prev owner used a different product in the cooling system for an intake leak which ended up clogging the return hose for the overflow tank and the engine overheated.

Since the engine has 200kmi and was only loosing about 1qt per month it’s just not really worth my time for a proper repair and having the heads resurfaced. I’ve tried a few other products which managed to clog up the cats more than the head leak.

At any rate, about 2 months in with this sealer and coolant level and staying rock solid. The trick to any of these sealers though is use the least amount possible. I got the 16oz bottle but for my 5 gal system I only used 4oz.

More is NOT better. If the weather is warm enough, especially if dealing w/ a larger leak where you need a more concentrated ratio, it’s best to do a heater core bypass while this is working initially.

This does have some particles in it along w/ the sodium silicate, equivalent to finely ground pepper. Shouldn’t clog up other components but why risk it. Once it’s fully distributed through the system it shouldn’t be an issue.

Short term, this is already the best product I’ve tried. We’ll have to see how it holds up 6 months-1 year down the line.

This thing saved me thousands of dollars. I thought of taking the time to write a review because this is the best $20 I have ever spent. I actually used it three times already over the course of 2 years.

So yes. over time I think you will need to use it again. In my case it took about 5-7 months before the coolant started leaking badly again. Then I purchased another bottle and it did the job again for my 04 dodge ram 1500.

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, and i was able to pass inspection twice. Before i used it for the first time, my truck was about to give up after 3 years it was leaking from coolant to engine (mixing with the engine oil).

The only solution was a rebuild or get a new engine that would cost over $3500. It is a great product. Not perfect, but if you have an old car with a leaking coolant system, and if don’t want to start spending thousands of $, this is the best product you can find (I tried 2 others before this one, and it was not as good).

PROS: stops leaks! CONS: a little THICK so you need to follow the directions and add liquid before using. It looks like MUD so it makes you apprehensive to use. Polaris UTV’s seem to be notorious for not holding water and running hot -for no apparent visible reason.

I put this in my Polaris 570 UTV that would not hold water/antifreeze. IT STOPPED THE WATER LOSS!! I have always shied away from such products because I though they were worthless and only plugged up things.

After having to add water to my 2017 Polaris since purchased NEW, I gave this a try and it worked. NO adverse affects – the heater still works great and it keeps the same engine temperature as before.

I added water one time and never again.

Tremendous and safe for your cooling system. Stopped my streaming leak the size of a pencil lead when other brands couldn’t. The pellets are the difference and what makes it “heavy duty” capable of plugging the larger leaks.

Important to idle the engine at least 30 minutes and until the leak visibly stopped. Been permanent since I then added 4 Oz of K-Seal product with (copper small enough) highly precision and smallest particulate to make it suspended then available for any future seeping that could develop, miracle that its really “cementing” where it’s needed to prevent any later seeping.

My Toyota with temperature controlling hvac works fine and wasn’t diminished for heating and a/c, engine cooling system working normally. I expect to be able to get continued service on the radiator and when it’s diminished I’ll replace it.

Tremendous!.

Coolant was spewing. Thought it was the water pump. Replaced that and then found the leak at the intake. Chevy s10 with 250K miles and I didn’t think it was healthy enough for major surgery, so tried this.

Still leaking after the first start, but then let it sit like the directions said, and then nothing. Not a drop. Been about 2 months and It’s still holding. I really didn’t think it would work, but it sure did.

Used a full bottle. Before, you use this, you will want to make sure that you don’t have coolant going into your enigine. Check you oil for any signes of water. This stuff works great in your water passages, but if it makes its way into you engines innards, I think really bad things can happen.

I purchased this product. I think that it works well but not for my particular radiator. I had a big leak that only allowed me to travel about 10 miles before the coolant temperature began to rise. I then added the entire bottle of this product and it held the coolant in the system longer.

I was able to drive 70 miles before the coolant temp went up again. Turns out that the plastic radiator tank on the driver’s side of my 1998 Chevy Blazer had a long crack measuring about 6 inches from top to bottom right at the center.

I can see where the product sealed the ends of the crack but couldn’t seal the middle part of the crack. The radiator would only leak in the morning when I started the car cool. Once it got warmed up the leak would be less drastic.

Overall, I would buy this product again. I do feel a little more power in the engine. The product might have sealed an internal problem that I was unaware of as mentioned on the bottle. It fixes a few things other than the radiator.

I ended up purchasing a new radiator (of course from Autozone). I installed it and now the car is running nice. Keep in mind that if your particular problem requires you to replace your radiator, get a plastic brush like the ones that come this a dust pan and brush the back to the condenser side that faces your radiator.

I brushed mine really good before installing the new radiator and now my air conditioner blows a lot colder. I hope this helps anyone who has a similar problem. By the way, NEVER RUN YOUR ENGINE WITH WATER ONLY.

YOU WILL DESTROY THE SHAFT SEAL ON YOUR WATER PUMP AND THE ONLY WAY TO FIX THAT IS TO REPLACE THE ENTIRE WATER PUMP. WATER WILL NOT MAINTAIN LUBRICATION ON THAT SEAL. USE THE CORRECT COOLANT FOR YOUR CAR.

IT COMES WITH THE PROPER LUBRICANT ALREADY IN IT. Best of luck to you all.

Every morning without fail I would see my bottom sump covered in coolant and a small puddle of coolant on the ground. My car was using about 80ml ever time I drove to work and back and had to constantly keep topping up my coolant tank.

I was sceptical at first with these types of products and read comments how it can block your heater cores and radiators. Thought I give it a go had nothing to else to loose and repairs would have cost a lot even just by replacing a seal or gasket because of being a European car you have to take everything off to get to certain parts.

I had no expectations with the use of the product after first use the leak stop but I do drive my car hard with boost and while doing that one day that hole opened up again but not as bad only like a 10 cent size leak at the area it kept like that for ages going away and coming back only when I drove hard but in less then a month even giving the car more power in a ECU tune it has never leak once yet and the coolant tank remains at the top maximum line.

Great product especially for the price and worth giving it a go like in my situation it can work for you depending on how severe and big your leak is. I do think this is only recommended for small holes though.

Every time when I switched off the engine of my old Landcruiser 1hz the pressure in exhaust / head decreased (obviously) and the pressure in the cooling system that still existed caused coolant to be pressed into the combustion chamber through a minimal crack in the head gasket.

Hence white smoke on start up and minimal coolant loss. So I thought it would be a good idea to try K-seal. I followed all the instructions and at first I thought it worked as the white smoke was gone immediately.

However a couple of hours later the engine overheated cause coolant and k-seal foamed heavily. I flushed the cooling system with a coolant flush to get rid of the slushy mix but no chance. Flushed with water afterwards at least 5 times but theres still residues to be seen and bubbles in the coolant now which i cant get rid of.

In the end the product made everything worse and ruined my cooling system on top of the head gasket crack – dont buy it!! May work for radiator leaks, but definitely not for head gaskets. Bad product in my opinion, as it is specifically advertised as head gasket repair.

PS sorry for my bad english.

Noticed some coolant on the ground one night, 50 cent size puddle, the leak started from a bottom corner of my radiator where the metal bracket and plastic joins. I was hesitant trying this product after reading reviews but it has actually worked, the leak stopped the day after i ran K-Seal thru the system, its been 6 months now and still no leaks, saved me buying a new radiator, for now anyways! If it was gushing out coolant however i doubt this product would work for anything bigger than a hairline crack, i must have just caught it in time to seal it.

Car was a Holden Astra TS.

With a seeping head gasket on our 1991 Vanagon, and not yet able to afford the expensive repairs, the Liqui Moly Radiator Stop Leak has held the leak at bay and given us many more kilometres on a tired engine.

A flush is not required which makes it more convenient, especially on a Vanagon that takes 18 litres of coolant. I would definitely recommend this product and will continue using it as needed.

Follow the instructions. Stopped a small leak on the radiator immediately. Still working 6 months later.

Used it to waterproof a rusting splash pan on my stove. Sealant works well and hasn’t changed appearance in 2 weeks of use at high temperature (~300 F). Although, it still feels a bit sticky. Definitely recommend.

One of the most important parts of a pellet stove installation is to protect the pipes from leaking smoke into your home. Seals pipes completely and goes on smoothly for a perfect seal. Shipped fast and free.

The motor was a perfect fit. Very happy with the purchase. Thank you.

This has to be the worst garbage that I have ever put into my car. I was losing fluid levels and overheating so I checked to be sure that the oil wasn’t milky, inspected the hoses, changed the thermostat, flushed the radiator and the heater core as well as inspected the water pump but couldn’t find a profound leak.

At this point, on a short time budget, I put the Bar’s radiator stop leak in the car. I was kind of grossed out by its appearance. It was thick and gloppy and I was a little apprehensive as I squeezed it out from the bottle and into the radiator but it was supposed to work according to the label and reviews, right? Over the course of the week the car started to be sluggish then difficult to start, then, all trouble broke lose at the worst time.

Between work, appointments and regular daily life, within a 5 day period I blew 3 hoses before checking the thermostat again and found that it was completely clogged with the sludge that plopped out from that bottle.

I eventually realized the root of my problem was a faulty radiator cap but not until after the costly repairs needed that were caused by this product. I am so frustrated that I fell for the “Magic in a bottle” theory that Bar’s bestows.

Powder a bit difficult to get into radiator without a VERY dry funnel, so it caked up near radiator neck. Unfortunately, even after 600 miles driving in all conditions, it still didn’t fully seal all leak points (assuming multiple ones).

I even used entire contents (rated for 22 quart system) despite my system being only 7 quarts capacity. I would say it was about 50% better though. I’m going to try a different product.

If you can locate the leak, I honestly suggest to fix it if you are in a lacation to do that. On the road and far from home sometimes makes that a less than desirable choice. My problem is that on my daughters car, and one of mine, I was losing small amounts of coolant daily, but could not find any visible leak, even under pressure.

I checked many locations and just could not locate it. Finally decided it was either in a location that as it slowly seeped it was turned to steam and evaporated, or internal to the engine, somewhere.

So I added a 20 gram tube of alumaseal to each radiator and drove about 20 or 30 minutes. Loss of coolant stopped immediately. Both cars. 6 months ago on her car and 1 month ago on mine. There has been no after affect on either car, heaters, valves, pumps, etc.

I personally think this is the best product I have ever used. I have no plans to remove it, because if I did, I still would not know where the original leak was.

My vehicle has over 140,000 miles. There have been few mechanical surprises with it. Recently, antifreeze started leaking from the system. Several times, I just added 50/50 antifreeze. I was at AutoZone to get more antifreeze and decided to try this product to fix the leak.

Easy to follow instructions. It has successfully repaired the cooling system. I haven’t added antifreeze in over a month.

I was advised by my garage there was a small leak in one of the lines going to the radiator, he then advised me to get stop leak. We drove to Halfords purchased this product and added it to the water tank.

You are then instructed on the bottle to run the car for 5 min, home was 10 min away. By the time we got home Problem Fixed. Over the moon with this product, saved us on mechanic fees Staff friendly and helpful, directing us to the correct area to find what we were looking for.

Good for a temporary fix if your car is needed for driving before getting a full on fix. I own a range rover and noticed coolant light come on and over 2 days i lost around 5-7 liters of coolant. my local garage was not able to take the car in to find issue and fix for two weeks and with me needing to drive the car daily there was no way i can put the car of the road for 2 weeks.

so i after some research online, though i would give this a try as a temporary before getting the car into the garage. Note this is a silver thick liquid and seals cracks in metal parts or seals. it wont fix broken pipes.

also don’t use more then one bottle as it will damage or clog your vehicle and on small cars only use half bottle. I will be getting the garage to flush the coolant system when its fixed. but it currently holding the leak and letting me use the car again.

so worth £6 ! hope this helps some people out there.

Had a small leak behind the heat exchange going into the combustion chamber, lost about 0. 1 bar a day so was topping up every day or two. Since the boiler is old and the heat exchange itelf was most of the cost of a new boiler to replace, I figured that a new one was on the horizon.

While getting prices I remembered this product existed and thought for £20 it was worth a shot to simply slow the pressure drop down for now. Put it in via a towel radiator plus some inhibitor for good measure while I was there.

A day or so later the pressure had stopped dropping and there was no evidence of the leak anymore. I topped back up to just over 1 bar, and that’s where it’s been when I check each day for about a month now.

I know it’s not a long term fix, but I can at least put off buying a new boiler for a little longer thanks to this. If you’re in a similar situation and have a system that this product is compatible with, then I’d definitely say give this product a go!.

My boiler was losing pressure slowly, checked all the obvious locations on the radiators and boiler. Presumed there must be a crack in a pipe under the flooring. Thought I would give this stuff a try, easy to use, took about 10 minutes to get the liquid into the sealed system.

Can’t confirm it has works as will take a few days to travel around the heating system. Ease of use gives it 5 stars alone.

I was skeptical about this and had tried some Fernox external leak seal that just didn’t do the job. A radiator tail was weeping ever so slightly, perhaps one drop every few hours, but it would have been difficult to nip-up or bind with PTFE since it was soldered to a succession of end feed copper joints I didn’t fancy disturbing.

I used a syringe and some tubing to extract around 500ml from the same towel radiator that had the leak and squeezed this stuff in, which is not too easy as it’s as viscous as 100W oil! I ran the system for a few hours and the leak was still apparent.

However, within 48 hours it had dried up and not yet returned so this product gets 5 stars from me.

I installed a new water pump and radiator after a marathon effort on my ml270 Merc and found there was still a leak coming from either the water pump or thermostat. Because these were new parts ( water pump – radiator) the last thing I wanted to do was gunk them up with stop leak.

That said I also didn’t want to sacrifice another few days getting to a very difficult water pump. So off to supercheap I went and bought this stop leak. Was a bit worried that a) the car would overheat and b) I would gunk my radiator.

Three weeks in and my car hasn’t overheated once, nor has the leak returned. I was losing about +200ml a week of coolant and now that’s stopped. So yes this product absolutely worked for me. Has it gunked up the new radiator and water pump? Who knows but for now I’m seeing no issues at all and for thirty dollars my problem solved.

This is my work and older car. If it was something newer or worth more I would probably look at fixing the leak but after days of wrenching away and still having a leak I’m glad this worked without any subsequent issues that I’m aware of.

Great product!.

Overhauled Nissan Patrol with upgraded radiators and intercoolers. Used two other brands (cheaper options on SCA shelves) they lasted under two months and other under two weeks. ONE PIN HOLE! I took some advice and grabbed a bottle of Rislone Aluminium Radiator Stop Leak Fixed and has sealed correctly and held up when off-road and towing.

I wish I used this straight away.

Had a pinhole leak in my radiator that water was streaming out from. Didn’t have the time to replace the radiator as its in a 2000 jeep grand cherokee laredo 4l with limited space to remove the parts required to get the radiator out.

So instead brought a bottle of rislone aluminium radiator stop leak, followed the instructions and put it in. Ran the motor for the time required and no more leak. It’s been 3 weeks and still no leak.

Have to replace the radiator eventually when I find the time but happy with the outcome of this stop leak.