K&W Engine Block Sealer for Head Gasket Leaks


I have a blown head gasket or cracked block.  The coolant test came back positive for combustion.  I’ve tried Bar’s Leak Block Sealer and K-Seal.  Neither worked.  The coolant is bubbling out of the expansion tank so I’d say the sealer isn’t even making it to the crack as the compression is pushing it back out the tank.

Before this I did have a water pump gasket blow and I used the K&W sealer and it did fix it.  I didn’t do the 500 mile thing as I did not read about it yet.  My question is will the K&W 500 mile trick work if it’s getting blown out of the expansion tank.  K-Seal Rep told me to put it in a top radiator hose so it goes directly into the block but that did now work either.

I really don’t want to pull the heads on this if I can get some sealer to work.



Hello Dan

Yes in my experience KW block sealer is the only thing I have seen very impressive permanent results but use as I direct not as per can.

Keep me posted

Austin Davis

Reader Follow Up
If I put it in the expansion tank it will just blow back out like the others.  Where should I put it in at?  Putting the K Seal in the top radiator hose by the thermostat did no good.



Hello again Dan

Are you absolutely sure the radiator is not restricted ….sure sounds like it. If there is that much back pressure from exhaust gases I would expect the cylinders to be full of water as well. A radiator that is stopped up at the bottom will not allow coolant to circulate.

Remove the upper radiator hose from the engine and pour the contents into the radiator. Butttttt check it out first

Austin Davis

Reader Follow Up


I just ordered a new radiator on ebay as that is problem my main problem and what caused the head gasket failure.  I remember I had to change the back heater hose assemble due to some of them being rusted out.  That rust probably clogged up the radiator which then caused the overheating and head gasket and water pump gasket failures.

Thanks for all your help.  You’re a very good man for doing what you do.


No problem Dan
Thanks! Fingers crossed, keep me posted. I would replace the radiator and thermostat first and see what happens before using the sealer or anything else

Austin Davis


1. Drain the cooling system of all (as much as you possibly can) of antifreeze

2. Mix a can of K&W Engine Block Sealer or Nano Tech Version in a bucket with tap water and mix thoroughly.

3. Fill up the radiator slowly with that bucket mix and top off system with tap water.

4. Drive the vehicle for a total of 500 miles, then drain out sealer and refill system with coolant and water mix (usually 50/50)

I do not mess with removing the thermostat or pulling the spark plugs etc. as it says to do on the can. We have been doing it this way for MANY years with great success.

****You will not have any freeze or boil over protection, so during the 500 mile period keep your engine and radiator from freezing weather. Ok!

Posted in: Over Heating

About the Author:

Austin Davis, consumer car repair advocate. "Hi there! I love to help people solve their car repair problems and I hope my site was helpful to you today. Thank you for stopping by."
  • Cleo Elizabeth

    Dear Austin everybody says I have a blown head gasket there are bubbles in my overflow when car is running but no white smoke how servere is it? It does keep getting the hot coolant temp message if I use :| how much water do I mix? Equal to? My heat I’d cold but my a.c. isn’t a.c. temp either help please

  • Bob Faulds

    I have an engine that is leaking coolant into the exhaust. How do I know this, t is going somewhere & not on the ground. At slower speeds, it shows no problem. Only does it give a problem, is when I get on interstate & take it up to 75 or 80. What I think is happening is that the engine runs normal till it starts building BTU’s. At that time, there is expansion between head & block. What, is the best fix, short of pulling the heads & putting new gaskets, head bolts?

  • Austin Davis

    In the plastic overflow bottle

  • Mitch

    I have a 1996 Ford Crown Victoria and there is no radiator cap. Where do I add the K&W block seal?

  • Austin Davis

    Yes, just a total of 500 miles before you flush it out and go back with coolant and water mix.

  • Tony Pieras

    using the K&W engine block sealer can I divide the 500 miles at 100 miles per day?
    Thank You
    Tony Pieras