How to Test for a Blown Head Gasket

how to test for a blown head gasketThere are a few different ways to test for a blown head gasket, but the easiest of them all is to check for multiple symptoms of a blown head gasket all happening at once.  At the end of the day, all of these symptoms could be happening together and, even though the chance is small, you may still not have a blown head gasket.

This article will be dedicated to the no question TESTS that can be done to for sure prove you have a blown head gasket.  All of these tests if they come up negative will still leave you questioning, but if they turn up positive then you are guaranteed to have a blown head gasket.

Here are the tests available to you:

How to Test for a Blown Head Gasket

  • Cooling system chemical test
  • Hot block pressure test
  • Cooling system pressure test

Chemical Test

The first definitive test you can do is a cooling system chemical check.  First, purchase or rent a chemical test kit from your local auto parts store.  Then drain enough coolant from your cooling system so you can idle your car with the radiator cap off and coolant doesn’t boil out.  Then use the test kit to test for the presence of exhaust gas in your cooling system. The only way exhaust gases could get in your cooling system is if you have a blown head gasket.

Pressure Test

The next definitive test you can do is a hot block pressure test.  As the name suggests, this test is best done when the engine is hot.  You can attempt this test with the engine cold which is much safer, but if the leak is small it won’t show up without when the engine is cold.  You will first need the proper fittings to attach an air compressor to your spark plug threads. Next set the piston you’re testing to bottom dead enter and add air pressure up to 100 psi slowly to the cylinder.  Next, watch the radiator for air bubbles in the coolant. The only way for air to travel from the cylinder to your radiator is if you have a blown head gasket. Make sure to leave pressure on the cylinder for a few minutes while watching for bubbles to test for the smallest leaks.  Also, if you choose to do this test hot, be EXTREMELY CAREFUL to not burn yourself or damage your tools.

Cooling System Test

The last test you can perform is a cooling system pressure test.  You will need a pressure test kit and time to let things sit.  If you pressurize the cooling system and have a leak, coolant will slowly make its way into the combustion chamber.  If you let the pressure sit on the system for a few hours you can check for the presence of coolant in your cylinders by using a boroscope to check for coolant through the spark plug openings or for a larger leak, simply start the engine and look for white smoke.

If you have one of these tests positively identify a blown head gasket and the hard part repair doesn’t make sense for your vehicle, consider using BlueDevil Head Gasket Sealer to seal the leak in your head gasket getting your car back on the road!

You can pick up BlueDevil Head Gasket Sealer at one of your local auto parts stores like:

  • AutoZone  
  • Advance Auto Parts
  • Bennett Auto Supply
  • CarQuest Auto Parts
  • NAPA Auto Parts
  • O’Reilly Auto Parts
  • Pep Boys
  • Fast Track
  • Bumper to Bumper Auto Parts Specialists
  • S&E Quick Lube Distributor
  • DYK Automotive
  • Fisher Auto Parts stores
  • Auto Plus Auto Parts stores
  • Hovis Auto & Truck Supply stores
  • Salvo Auto Parts
  • Advantage Auto Stores
  • Genuine Auto Parts stores
  • Bond Auto Parts stores
  • Tidewater Fleet Supply
  • Bumper to Bumper Auto Parts
  • Any Part Auto Parts
  • Consumer Auto Parts

Pictures Provided By:

blown_head_gasket.jpg – By Malkovstock – Licensed by Getty Images – Original Link


12 responses to “How to Test for a Blown Head Gasket

  1. I replaced a expansion plug in the right rear head of my 94 mustang 3.6L . Had radiator filled but not totally full and started to crank it over to start it and wouldn’t and hasn’t yet? Took cap off and fluid was pressurized and blew out and came out as I turned it over. Any ideas?

    1. Paul-

      Thank you for asking about your Mustang. Did it start to crank and not turn over or did it seem like it wouldn’t crank at all? Was the system bled? 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!


  2. Hello, Can you use the Blue Devil Head Gasket Repair solution on an 8 cylinder vehicle? The bottle says 4 or 6 only. Is there another option for 8 cylinder engines?

    Thank you!

    1. Jill-

      Yes, you can still use the BlueDevil Head Gasket Repair on an 8 cylinder engine. The amount of product to use would depend on the cooling system capacity. Most 8 cylinders would require two bottles of the BlueDevil Head Gasket Repair.

      Thank you!


  3. I’ve been having bad luck with my vehicle. Paid for vc and timing cover reseal. When finished they advised me of a slight main seal leak. So I used your main seal sealer. Now i see white smoke from my exhaust on start up which dissipates but then there is some blue smoke. I’m guessing head problem. I’m going to try one of you head gasket products but what is the difference between the 3 listed? Also are they compatible with the main sealer? Thank you.

    1. Bob-

      Unfortunately, we do not manufacture a product intended to stop oil from leaking from the head gasket. Our Head Gasket Sealer products are only intended for water/coolant leaks. Replacing the head gasket may be your best option.

      Thank you!


    1. James-

      The BlueDevil Head Gasket Sealer does not contain any solid or particulate matter, so it is a non-clogging product. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!


  4. Can you use this product in diesel tractors? I’m sure my ford 3000 has a blown head gasket. There are bubbles in the radiator with the engine running and the cap off. After about 30 minutes of cutting grass it spews antifreeze out the overflow hose.

    1. Darrin-

      Yes, the BlueDevil Head Gasket Sealer is safe and compatible to use in diesel tractors. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!


  5. can a coolant pressure test be trusted if the system is only half full? I had a new motor put in my 4r 22re and when I got it back only half the coolant was in. It smokes at start up. will running a car with half the coolant prevent the thermostat from opening, an air pocket? I think the shop did the first test run and over heated the motor and damaged it. it runs good otherwise. The shop declared they did a coolant pressure test as part of the install, but seems to me an air pocket or even not having the thermostat open would give false results. I also had a scope test done later, with pressure on coolant system, but I can only assume they did it on a operating temp motor with the thermostat open. They found nothing in the cylinders.

    1. John,

      Yes a pressure test on your cooling system will still work even if the system is only half full of coolant. A good mechanic can often tell how full the cooling system is by the pressure test. If there is air in the cooling system then it will take a lot more air to pressurize the system because the air bubble is compressing during the pressure test. Whether there is air or coolant in the system once it’s up to the pressure of the test if the pressure doesn’t drop it confirms the cooling system is tight and won’t have any leaks.

      Thanks again for your question!
      -BD Auto Pro

Leave a Reply

Your email address will not be published. Required fields are marked *