Symptoms of a Cracked Block

Cracked BlockHaving a cracked block can give a variety of strange symptoms that can be hard to identify and diagnose.  Like many problems with your cooling system, a cracked block often can mask itself during normal operation of your vehicle and only reveal itself during certain conditions making it extremely hard to diagnose.

Having a cracked block has to do both with the normal use of the vehicle and the construction of the engine itself.  When vehicle manufacturers are designing engines, then want to make sure the engine is sturdy and able to withstand the stresses and strains that will be on it both from the combustion process and from the heating and cooling cycles the engine will go through.  On the other hand, the weight of the engine has a lot to do with how to the car performs.  A heavier engine will decrease fuel mileage due to the extra energy required to get all that weight moving from a stop.  A heavier engine can also affect the handling characteristics of a car as the added weight can affect the center of gravity and its ability to corner well.

As engine manufacturers try to balance building an engine that is both lightweight and strong they have to account for all the stresses the engine will go through.  The pressures of combustion are high, but rarely high enough to significantly affect your engine block.  The more prominent stress on an engine is the heating and cooling cycles it endures from starting and stopping the engine.  The heat comes from the combustion process and is spread to the rest of the engine through the flowing coolant.  As the metal gets warmer it expands but at different rates depending on the temperature gradients.  Combine that stress with the normal vibrations of driving, braking and accelerating you can get huge stresses in different parts of your engine block.

These stress, after many miles, can lead to failures and small cracks to form.  Engine blocks rarely crack quickly.  The crack usually starts as small cracks that leak only a tiny amount of fluid and only when the engine is hot and the cooling system is pressurized.  Since most engine blocks are cast iron, once a crack has started, it is almost impossible to stop.  Because of the way the metal molecules settle into a lattice as the block is cast, cracks can easily propagate through the metal once they’re started.  This means that if you do have a cracked block, the leak will often get bigger quickly.

This leads us to one of the main symptoms of a cracked block.  A cracked block will almost always cause a cooling system leak and start very slowly.  Sometimes it will be so slow that you will only be able to notice the leak when your car is warm and it will just look like a small amount of steam.  As you continue to drive the heating and cooling cycles will enlarge the crack until you notice more steam, then possible drips of coolant and eventually a leak that will lose water whether the engine is warm or cold.

The other symptom of a cracked block that can be confusing is that the crack is often in the corner of a gusset or near a ridge in the block where the metal goes from thick to thin.  These areas are often very difficult to see without a mirror and flashlight or by removing the block.  These areas are often away from other coolant hoses and can be confusing.

If you discover a cracked block in your vehicle, don’t worry!  You may not even need to take your car to the mechanic’s shop to stop the leak.  BlueDevil Radiator and Block Sealer is a safe and easy to use sealing agent that can repair a crack in your cast iron or aluminum engine block without using tools.

For more information about BlueDevil Radiator and Block Sealer, click on the banner below!!






You can find BlueDevil Radiator and Block Sealer at any of our partnering local auto parts retailers like:

  • AutoZone
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  • Bumper to Bumper Auto Parts Specialists
  • S&E Quick Lube Distributer
  • DYK Automotive
  • Fisher Auto Parts stores
  • Auto Plus Auto Parts stores
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  • Genuine Auto Parts stores
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  • Bumper to Bumper Auto Parts
  • Any Part Auto Parts
  • Consumer Auto Parts

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cracked_block.jpg – By Daseaford – Licensed by Getty Images – Original Link

26 responses to “Symptoms of a Cracked Block

    1. Frank-

      Yes, the BlueDevil Radiator & Block Sealer, and both of our BlueDevil Head Gasket Sealers are safe and compatible to use on aluminum blocks. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!


  1. My mechanic says that probably I have cracked block. The symptoms are presence of small amount of engine oil in coolant but no coolant is in engine oil as the dipstick and oil cap shows no signs of coolant in the oil. Can this product help to overcome problem?

    1. Hello i am having this exact same problem & i am wondering if you can tell me your solution my name is Aynice can you please contact me at 214-574-8407

  2. My 3.2 ltr 4M41 turbo diesel Pajero Exceed 2006 will start and run normal after the engine heats up it blows white smoke could this be the EGR valve.

    1. Simon-

      Thank you for asking about your Pajero Exceed turbo diesel. Unfortunately, white smoke coming from the exhaust pipe is a tell-tale sign of a blown head gasket. Are you noticing a loss of water/coolant? Is the vehicle overheating at all? Please contact our technical support line at 888-863-0426 so that we can get a little better understanding of the vehicle’s condition and be able to make any appropriate recommendations.

      Thank you!


  3. I have a 2000 Chevy Cavalier. It overheated accordi h to the dashboard gage. I stopped immediately at a gas station and turned the car off. There was no smoke or steam. The coolant bottle was empty. I filled it 5 days prior. There was no leaking in my garage nor my parking space at work. ????

    1. CAM-

      Thank you for asking about your Chevy Cavalier. Please contact our technical support line at 888-863-0426 so that we may get a little better understanding of the vehicle’s condition and be able to make any appropriate recommendations.

      Thank you!


  4. Hello,

    I would wish to purchase the Radiator & Block Sealer (item number #00205) but each time I tried to confirm the payment, I got the following error message:

    “Something went wrong when trying to process your payment. Please review the error message and try again:
    This transaction has been declined”

    For your information, I am from Mauritius Island.

    Could you please suggest ways to properly confirm the payment?

    Thank you.


    1. Jonathan-

      Thank you for your interest in the BlueDevil Radiator & Block Sealer. Our credit card processor is very sensitive to international orders to prevent from fraud.  When placing the order make sure your billing address matches exactly what you have on file with your credit card company. Otherwise, you may contact us at 888-863-0426 to place an order over the phone.

      Thank you!


  5. I am having a problem with oil pressure. it starts off good @60lps but as the engine warms up it drops to 8-10lps at idle. the block is a 454 rebuilt twice but has the same issue. everything was checked except the block. after the first rebuild I had some overheating issues which hopefully have been resolved. could an oil galley have cracked to cause the problem.what are your thoughts

    1. Mike,

      Thanks for your question about your 454 oiling issues. It is possible you’ve got a crack in the blog but the only way to discover that problem would be to pull the engine, tear it down, and have it magnfluxed. Before you try all that it may be worth installing a high pressure/volume oil pump or trying a slightly higher viscosity oil. If the engine has been rebuilt twice it’s possible that you simply need to run a thicker oil to compensate for larger clearances depending what type of machine work has been done.

      Thanks again for your question!
      -BD Auto Pro

  6. Hello,
    My 2000 subaru outback just recently started overheating after the coolant froze and we failed to notice before driving (northern MN winters!). I brought it to a mechanic and they replaced the coolant, but the engine still overheats. It overheats, but also cools back down very quickly. They thought it was a blown head gasket but for some reason (call it intuition) I am hesitating to believe this. Plus I don’t notice any of the tell tale signs that it is blown head gasket. So I am wondering if it could be a cracked engine block? I would really appreciate any feedback you may have. Thank you.

    1. Colin-

      Thank you for asking about your Subaru Outback. Are you noticing any water/coolant loss? It is possible that you are getting combustion/exhaust gases pumping back into the cooling system.  You can use a “Block Dye Tester” to confirm whether or not that is the case.
      If that is the case, BlueDevil Head Gasket Sealer will still work if your vehicle is getting combustion/exhaust gases blowing into the cooling system and creating pressure.  To give yourself the best overall chance of BlueDevil working successfully, in addition to the directions, you should remove the spark plug from the cylinder with the leak; this will be the spark plug from the cylinder with the low compression reading.  If you are not sure which one that is, you may pull all of the spark plugs and will notice one will have a white-crystal-like substance on it and/or may look dirty; this is the plug you should pull.  Leave that plug out for the 50 minute idle in order to relieve the pressure from building up and thus allowing the product to seal properly.  Be sure to follow the guidelines for the proper amount to use based on the size of your cooling system.

      Thank you!


  7. My car finishes it’s water after a month, I changed the head gasket, water pump and thermostat and I can’t seem to find any leaks. Which blue devil product do you recommend ?

    1. Mure-

      Have you noticed any other symptoms with the vehicle besides losing water? Please contact our technical support line at 888-863-0426 so that we an get a better understanding of the vehicle’s condition and be able to make any appropriate recommendations.

      Thank you!


  8. My 1999 Ford f150 was running good, let a family member use it and they never told me I had a coolant leak until I was driving it to work 1 morning and it wouldn’t let me drive more than 20 miles per hour. Let a mechanic look at it and he said when the anti freeze leaked out they just replaced it with water instead of fixing the freeze plug and putting antifreeze back in it so the water froze during winter causing the ice to expand and crack the block what can I do about this situation. Thank you in advance.

    1. Tony-

      Thank you for asking about your Ford F-150. To confirm, are you losing water/coolant from the block and the freeze plugs as well? How quickly are you losing water/coolant? Please contact our technical support line at 888-863-0426 so that we may get a little better understanding of the vehicle’s condition and be able to make any appropriate recommendations.

      Thank you!


  9. I have a 2001 Ford Taurus. It is leaking coolant from, what looked like, the lower radiator hose near the water pump. I replaced the lower hose, put everything back together with fresh coolant and started it. Still leaking. I can’t see where it’s coming from. I replaced the water pump a few years ago so I’m thinking if it were going to leak anywhere from the water pump, it would have done it before now. I’m thinking it maybe a crack in the engine near the water pump. Or the timing cover gasket is bad and it’s leaking there. I just can’t tell for sure because it’s to tight to see. Should I use your product before I take it to a shop or just take it in? I mean, will it harm anything if I try it first? Thanks.

    1. Tom-

      Thank you for asking about your Ford Taurus. Based on your description, we recommend using the BlueDevil Head Gasket Sealer. AS long as you are not losing coolant too quickly, and the vehicle can maintain idle for a full 50 minutes, you would be a great candidate for the product. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!


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