K&W Block Sealer

K&W engine block sealer

How much KW Sealer should we use? is the 16oz can enough for a Chevy s-10 dual core radiator?  Our truck over heated on my son Christmas blew head gasket and was blowing white smoke.

One mechanic  said  to replace the intake manifold and radiator,  a friend is helping fix it doesn’t think  the intake manifold is bad  so far we  did head gaskets & bolts a water pump, spark plugs and new radiator  after a oil & filter change  we still have oil that is milky.

He wants to do a compression test but I cant drive it there with out making it worse will this fix that?  Or should I wait  and have the heads shaved and a new gasket set

I am running on empty cash wise this month  and  really need wheels right now  but will wait if driving it will put it further in the hole  any advice would be greatly appreciated
thank you for your time


Hi there,

The 1 can of K&W Block Sealer is plenty for your vehicle. You will need to be able to start and run the engine for the sealer to work though. So if you have lots of water/coolant dumping out of the tailpipe where the engine will not stay running, the sealer will not work.

If you can get the engine to start and stay running, then use the sealer as I described on this site…not as per instructions on the can.

My tried and true instructions for Sealer are:

1. Empty ALL coolant from the engine, radiator as best you can – sealer will not work with coolant.

2. Pour contents of the can in a bucket, mix in plain tap water into bucket and stir contents.

3. Pour contents of the bucket into the radiator and top off with plain tap water.

4. Run the vehicle for 500 miles total drive time.  You don’t have to drive 500 miles all at once, but the faster you put those miles on the better.

5. After 500 miles, drain out radiator and fill up with 50/50 water coolant mix and pray that it worked. That is all, I don’t take out the thermostat or anything else.  We have had a 80% success rate on 100’s of cars in our shop.

Warning – You will NOT have BOIL OVER or FREEZE protection during those 500 miles so make sure to keep the engine and radiator from freezing.


Posted in: Head Gaskets

27 Comments on "K&W Block Sealer"

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  1. Austin Davis says:

    It wont fix a burnt valve, that requires a valve job but it will fix a blown gasket issue…you can try it if you want, wont hurt at this point.

  2. Jeff volkman says:

    I have a 2004 ford ranger 69,000 miles on it put new spark plugs wire etc also put 3 injectors on it still misfiring a little bit don’t have white smoke but a good amount of water coming from tailpipe any suggestions?

    • Austin Davis says:

      Get a cooling system pressure test to determine if you have an internal leak, if so, use the sealer. Water could be just normal condensation thanks to Ethanol gasoline, miss might be due to internal wear/damage in the cylinder or valves…a compression test is what I would do to check.

  3. Jake Wacker says:

    Should I run the heater while driving the 500 miles with the sealer in the systems? Or will that hurt it ?

    • Austin Davis says:

      Run the heater for a few minutes to remove any air pockets that might be in the system, then top off radiator as needed, but you dont have to use the heater anymore unless you need it. Wont hurt it.

  4. freda says:

    1997 deville smokes no oil in water but a lot white smoke when start up clears up after warm heater works great not running hot please help

    • Austin Davis says:

      I would get a cooling system pressure test first, but you might have an internal coolant leak, like a head gasket that is dripping cooling into the cylinders overnight. The sealer would be a good option if that is the case. I would expect you would be constantly adding coolant if there was an actual coolant leak, so check the radiator level.

  5. Chris says:

    I have a 98gmc sierra 5.0 305 and yesterday noticed there was coolant leaking from the back of engine coming out near the spark plug. I checked the oil and there are no hoses back there that I can see. I am assuming it is a head gasket issue, I have heard these trucks are prone to them. My question is the 500 miles are they supposed to be highway? Certain speed? Can you tow anything while you are doing this? It’s my work truck and kinda stuck without it. And advice would be great. Thanks

    • Austin Davis says:

      I would get a cooling system pressure test, I am thinking this is an external leak not a head gasket leak. But, if you have ruled out an external leak and are sure its internal, try the sealer, 500 miles anyway you wish at any speed, no towing if possible.

  6. Mandy says:

    Hi I have a 2002 dodge ram 1500 4.7 an it has a rough idle and has white smoke coming out and I changed the spark plugs and coils and it’s running rough and my friend said I have blown head gasket. I was gonna try the k&w and see if that works. I was wondering could it mess anything up is it’s not a blown head gasket. And could my catylatic converter be bad to.

    • Austin Davis says:

      First get a cooling system pressure test to determine if you have an internal or external coolant leak. You did not mention anything about overheating or coolant loss, and those would be present if there was a head gasket leaking. You might want to clean the throttle body to see if it helps with the rough idle http://youtu.be/BXwqBf4cqic?list=UU3qymK5ErdJDCwYhgtaylng the white smoke….usually means internal coolant loss, but it can sometimes just be condensation inside the exhaust system.

      But no, the sealer will not hurt anything else…unless you have a radiator that is already restricted with rust, the sealer will just get clogged up in the already clogged up radiator.

  7. Shelton Anderson says:

    Hi Austin:

    I have a 91 toyota corolla. Replace head gasket six months ago and still some leakage into cylinder 3 & 4. Yesterday I drained and flushed all the coolant out as best I could. Mixed 1 can of k & w sealer with water and installed in radiator. Topped it off and started driving car. Drove good until today. Topped off radiator again and as I drive car runs hotter than normal and the idle surges and idles too high. I have put about 50 miles on car and it starts much better. Any suggestions what my problem is? Could the sealant plug holes in the iac valve and coat the sending unit that starts the cooling fans? Thanks in advance.


    • Austin Davis says:

      Sorry for my delay, been over whelmed with questions lately. I would try to drive it a little longer and give the sealer time to repair the hole. You might want to re-torque your cylinder head to make sure that gasket is nice and snug on the head. The sealer will not plug up anything……….unless your radiator is already plugged up then the sealer will not be able to circulate. a restricted radiator is the main cause for overheating and head gasket failures. Its idling fast because it is overheating and trying to cool itself down.

  8. richard says:

    is it wise to run block sealant for 500 miles if its leaking into the oil

    • Austin Davis says:

      Well, what other choice do you have….remove the cylinder head and do a valve job. The sealer usually does its magic within a few miles but in some cases it can take a while to find and seal the leak. 500 miles is what we have been using for many many years and seems to be the magic number. Change your oil if you have a lot of coolant contamination.

  9. Smilinsmitty says:

    I am helping a friend (I thought I was helping) with his 98 Lincoln 4.6 front wheel drive. He had an obviously bad water pump, and I replaced it and the belt and new thermostat. I think while trying to get it home when the pump went totally bad,the engine overheated and lost his head gasket seal. He decided he wanted to use the K&W Nano-T stuff. All the obvious plumes of steam from tailpipes, and turbulence in the cooling system overflow tank. The car was getting hard to start when I was flushing it with cooling system cleaner so all ethylene glycol would be gone. The last time I got it started was on the last warm-up and drain cycle and the water was clear and I mixed the stuff per instructions, poured it in the upper radiator hose, and then the engine would not start. This was 24 hrs ago… My concern is what happened to the product in the cooling passageways and radiator. I have pulled the plugs and they weren’t fouled with water or gas, but I am thinking there may be water on the injectors causing it to not start. It has been on a battery charger today, and I am going to try starting it in a short time from now.
    My real worry is “did I just ruin this engine?”

    • Austin Davis says:

      Well the sealer did not ruin the engine, at least I have never experienced any kind of engine damage from using it and we have used it a lot over 30 years. I would first triple check your repair, make sure everything is plugged back in and there are no loose wires/connections.

      Then start ruling things out. Do you have compression on all cylinders or is there a lack of compression or timing issue. Do you have spark to all spark plugs, and is the spark strong? Do you have fuel and fuel pressure to the engine? Can you borrow or rent a manual fuel pressure gauge from your local auto parts store and check fuel pressure at the fuel rail at the rear of the engine?

      The cooling system has no bearing on the engine starting, you can remove the radiator/waterpump/hoses etc. and the engine will still start, just overheat. So this issue is either a lack of compression or ignition timing (timing chain broke, jumped a tooth) lack of spark (ignition coil, module, crank sensor etc.) or lack of fuel pressure from the pump.

      See what you can rule out.

  10. Jon Shea says:

    How long does it take after K&W additive before car stops rough idle?

    • Austin Davis says:

      Sorry for my delay Jon, It can take up to 500 miles for the product to really take hold and repair things, but usually within a few miles you can see positive results

  11. NICK says:

    Dear Austin,

    Thanks for what you do…I have a 1996 Silverado 305 with 149,000 miles that runs great, but has water in the oil. I just found the contamination this morning. K & W “Permanant Metallic” says not to drive with this head gasket sealer in the system. You advise 500 miles. Have you had this cause any additional issues? Will it clog the themostat?

    Thanks again,


    • Austin Davis says:

      Hi Nick, thanks for your kind words. Yes, my method and the manufacturer is slightly different. Driving with the product sure seems to work much better and much easier than their way…in my opinion and experience with using it. No, I have not had a clogging issue (unless your radiator is already restricted then it can make things worse) with the thermostat or any other issues.

      The main concern with driving with the product is without coolant you do not have boil over protection or freeze protection so you have to watch out for those issues. I would bet it will solve your problem in just a few miles of driving. People with more severe internal leaks (smoke out tailpipe, engine miss, quick loss of coolant) need to keep the product in the system longer than normal.

  12. Vinny Patel says:

    Hi Austin,

    So after I flush the system (as much as I can), will it be okay if I follow the instructions on the bottle(I got the Nanotechnology one) such idle the car ..and then after the waiting period, drive 500miles as you advice after which drain, flush and pour 50/50?

    Per your instructions above, Immediately after you put the sealant in the car, do you leave the car sitting there for a period of time before advising your clients to drive 500 miles?


    • Austin Davis says:

      If you want to follow my instructions, just add the bottle of sealer and top off with water, then put 500 miles in total on the vehicle before draining. You drive 500 miles in a day, week or month….just get enough mileage on the engine for the sealer to take hold.

      The newer Nanotech does seem to be a quicker acting product than the original, but I would still drive it a while until all white smoke from exhaust has stopped and coolant is not leaking.

  13. Justin Ferrara says:

    I have to admit that 80% isn’t the success rate I was looking for but I am very interested in trying your method. The only issue I am running into is finding the KW Block Sealant. I checked Amazon.com and found this product. Is this the correct product to use your method with?

    • By Austin Davis says:

      Yes, that is their “new and improved” product and is just as good and that is a great price, $35 at my local auto supply. 80% is a DARN good success rate for any type of sealer in a bottle.

  14. Dan says:


    Have you had any luck with K-Seal or Bar’s Head Gasket sealer?

    I used KW on the water pump gasket and it did work fine. Since then I’ve been losing coolant from overflowing from the expansion tank. (Makes the belt squeel like a pig! Any idea how to clean the antifreeze of those? Already bought a new belt now this one squeels)

    Getting a coolant compression test tomorrow. If it comes back positive for a head gasket or crack leak do I have to leave the KW in 500 miles? It’s still too cold here in Missouri to do that and i work night shift so it would be outside.


    • By Austin Davis says:

      Personally I have not tried those sealers so I really cant give you a comment either way. KW Block sealer works great, I CAN personally attest to that.

      Getting coolant on the belt, you pretty much got to replace the belt it just seems to soak it up and never stops squealing. I have tried many many times and have to give up in frustration and replace the belt.

      It does not sound like a headgasket problem, so get a pressure test, check the radiator for a restriction and system for an air pocket that needs to be bled out before doing anything else.

      The overflow/expansion bottle will fluctuate up and down, so dont get to concerned about the coolant level there as long as the radiator is full.

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