How To Tell If You Have A Bad Engine Head Gasket

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    A major problem on many vehicles is a bad head gasket and sometimes simple replacement of the gasket will cure the problem completely but other times you will need to have your block or head resurfaced by a machine shop. Before you get into a costly situation that can leave you without your car for many days or sometimes weeks depending on how bad it is you want to make sure that the head gasket is bad.

    What Is A Head Gasket And Why Do They Go Bad

    Most people understand that your engine has a number of pistons that ride up and down in their cylinder where gasoline combusts and then turns the engine to eventually turn the wheels of your car. On top of the cylinder that the piston rides in is your head. It is a large piece of metal that caps off your engine cylinders and it also has ports to allow your gas and air mixture to enter the cylinder and then other ports that take the exhaust and send it to your mufflers and out the back of your car. To do this there are valves that seal off the air fuel side from the exhaust side and all of this is in your engine head.

    Because the pressure in the engine is pretty high and the seal between the Head and the Engine needs to be leak free for many years there is a heavy gasket between the head and the engine that seals off the system.

    In addition to sealing off the combustion cylinders there are also water ports in the engine and the head that circulate your radiator fluid. They too need a good seal and they need to be separated by the head gasket from the combustion cylinder so your engine will run correctly.

    Ok so basically the head gasket seals off the head from the engine.

    How Does The Head Gasket Go Bad?

    In normal conditions your head gasket should last the life of your vehicle but there are things that cause it to go bad. The most common is that you run low on engine coolant and then the engine overheats. At that point the head or deck of the engine can warp and the gasket will fail. There are other conditions when the engine combustion chamber runs hot and it can burn through the gasket into a coolant pass through and it will need to be replaced. Some of the reasons also include manufacture defects and poor engine design. And the final reason would be normal wear and fluctuations due to heating and cooling and this would take a very long time for a gasket to fail if there aren’t other outside reasons including a bad gasket being used in the first place.

    Visual Checks For A Bad Head Gasket

    If a head gasket fails externally you might see coolant leaking from the side of your engine. You must make sure that this coolant is not coming from a failed hose, engine block plug, engine temperature sensor, or other external part but if you see coolant coming from the area where the head mounts to the engine you probably have a problem.

    If the gasket fails internally you won’t see fluid leaking from your engine but it will leak internally. It can leak into a an oil pass through and it will result in engine coolant in your engine oil. You can see this when you change your oil or check your dip stick. Normally you won’t see green coolant but you will see a milky goo that is very disernable from normal engine oil.

    You will also notice that your radiator is going empty. Normally you do not need to top off your engine coolant. If you are finding that you need to add radiator coolant once a week or at a unregular time interval then you need to check deeper.

    Air in your radiator is another problem. As combustion gasses escape through your coolant passages it will cause bubbles in your radiator if you take off the cap and look. This is not a perfect test but it is something to look for. Discoloration of the coolant is another thing. Coolant will discolor over time but in this case if your are topping up your coolant and your new coolant gets discolored very quickly its something to look closer at due to the fact your head gasket might have failed.

    Chemical Testing Your Coolant

    There are test kits that you can use to check for the presence of combustion chamber gasses in your coolant. Remember we were saying that bubbles might be present if the combustion chamber is forcing exhaust gas into your radiator fluid. This tester will look for the presence of these gasses even if you can’t see the bubbles.

    To use the tester you first remove coolant from the radiator with a turkey baster or pipet bulb as the directions say. What you are doing is removing enough liquid so it won’t enter into the tester.

    Place the tester in the radiator cap hole and then fill it with blue test liquid.

    Run the vehicle for a few minutes as the directions advise.

    The liquid will remain blue if there isn’t a problem or it will turn yellow if there is a gap in your head gasket.

    Chemical testing does not catch breaks in your head gasket that are not entering into your coolant system such as one piston chamber leaking directly into its neighbor but if they are there then the test will show positive and the head gasket will need to be replaced.


    Final Note

    There are a number of visual and diagnostic tests you can take before you commit to replacing your head gasket. If the tests show positive such as coolant leaking into your engine oil or combustion gasses leaking into your radiator then you will need to replace your head gasket.

    Replacing a Head Gasket is not the hardest job you might ever perform but for the backyard auto mechanic it can be difficult if you have never performed the service on your specific vehicle. If a mechanic has a situation where they need to remove a manifold and need a gasket to replace it then they can easily order it. If you do this at home you might not be able to get to the parts store easily and it will take more time and cause more frustration.

    This is one thing you might want to research about your vehicle if you think you might attempt this job yourself. However the tests above will let you know up front with only a few tools like the combustion gas tester .. if you are right in letting your mechanic replace the gasket.

    Additionally performance can or may not be an issue in this situation so it can be a difficult thing to make this repair without fully knowing if it is required. Go through the tests and read your cars shop service manual for more information.


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