Signs of a blown head gasket

A blown head gasket leads to such unpleasant consequences as engine overheating, poor heater performance, exhaust fumes from under the hood of the car, emulsion in the engine oil, white smoke from the exhaust pipe and some others. If you experience the above symptoms or one of them, it is necessary to check the cylinder head gasket. There are several ways to do this.

Below we will look at why the cylinder-head gasket blows, what consequences it leads to, and what to do if this trouble happened to the engine of your car.

Signs of a damaged cylinder-head gasket

If the cylinder head gasket is damaged, the sealing function will be impaired. Exhaust gases, engine oil and coolant may begin to mix with each other or burst out from under the head. Consequently, when the cylinder-head gasket is blown, the car owner will be prompted by the following signs:

Signs of a blown head gasket: video

  1. Exhaust gases come out from under the cylinder head. This is the simplest and most obvious sign. When the gasket burns through, it will begin to leak exhaust gases that will exit into the engine compartment. This will be visible visually, as well as perceptible by ear — there will be loud noises from under the hood, which is simply impossible not to notice. However, if the blowout is small, you should pay attention to other signs.
  2. A blowout between the cylinders. The external signs will resemble those that occur when the engine «trots.» There is a mixing of the fuel mixture from one cylinder with the exhaust in the other. As a rule, in this case, it is difficult to start the engine, but after warming up it continues to work steadily at higher revolutions. To determine the breakdown, it is necessary to measure the cylinder compression. If this happens, the compression value in different cylinders will be significantly different.
  3. Emulsion from under the expansion tank cap

  4. The penetration of exhaust gases into the coolant. If the cylinder head gasket is punctured, the exhaust gases may get into the cooling system in a small amount from the cylinder block housing. In this case, it is enough to unscrew the radiator cap or expansion tank. If gases in large quantities enter the system, the bubbling will be very active. However, when there is not much gas, than to diagnose use improvised means — cellophane bags, air balloons, a condom. We will touch the diagnostic method in detail below.
  5. Coolant gets into one of the cylinders. As a rule, this occurs due to a tear in the gasket between the cooling jacket channel and the combustion chamber itself. In this case, there is a thick white smoke from the exhaust pipe. And the level of the coolant in the tank drops. The more antifreeze gets into the cylinders — the more white steam comes out of the exhaust pipe.
  6. Oil is leaking outward from under the cylinder head. These facts can also be signs of the cylinder head gasket failure. That is, there is a tear in its outer shell. In this case, you can see oil leaks in the area of the joint between the cylinder head and the cylinder head. However, their causes can also be other.
  7. Foam in the expansion tank

  8. The significant and rapid growth of engine temperature. This phenomenon occurs because the hot exhaust gases get into the cooling system, as a result, it fails to cope with its tasks. In this case, in addition to replacing the gasket, it is also necessary to flush the cooling system.
  9. Mixing oil and antifreeze. Mixing antifreeze with oil is very detrimental to the engine, because the properties of the oil are lost, and the engine is forced to work in unsuitable conditions, which leads to its significant wear. This malfunction can be diagnosed by the presence of oily spots in the expansion tank of the cooling system. To do this, open the oil filler cap and look at the inside of it. If there is an emulsion there (it is also called «sour cream», «mayonnaise» and so on) of a reddish color — it means that the antifreeze has mixed with oil. It is especially topical when a car is standing not in a warm garage, but outside in winter. The same emulsion can be seen on the dipstick to check the oil level.
  10. As a result of the mixing of antifreeze and oil, an emulsion of yellowish (most often) color is formed. If it appears, replacement of the cylinder-head gasket alone will not do the job. It is necessary to flush the system from this composition. Including a pallet and oil channels. And it may cost you additional expenses, sometimes comparable to a complete engine overhaul.

    Wet spark plugs

  11. Bad work of a heater. If the cylinder head gasket is burned through, exhaust gases appear in a cooling system. As a consequence, a heater exchanger gets stuffy, and the efficiency of its work decreases. Often in this case the coolant temperature rises sharply.
  12. Pressure growth in the radiator connectors. If the gasket is depressurized, the exhaust gases will enter the cooling system through the spigots. Accordingly, they will become very hard to the touch, they can be checked simply by hand.
  13. The appearance of significant soot on the spark plugs. In addition, they may be literally wet due to the appearance of antifreeze or moisture in the cylinders.

A clear sign of engine overheating is the presence of condensation on its surface. This is also an indirect sign of a burned cylinder-head gasket or a crack in the cylinder block. First of all, it is necessary to make a computer diagnostics of the engine. The presence of errors will indicate the direction and possible additional faults. As a rule, these errors are related to problems in the ignition system.

Why the cylinder-head gasket blows

In most cases, the cause of problems with the head gasket is the banal overheating. Because of it, the cylinder-head cover can «twist», and the plane, by which the gasket is adjacent to the two contacting surfaces, is disturbed. As a consequence, there is a depressurization of the internal cavity with all the ensuing consequences. Aluminum heads mainly change their geometry. Cast iron heads are not subject to such malfunctions, they are more likely to give a crack than the warp, and even then in the most extreme cases.

Bolt tightening diagram

Also due to overheating, the gasket can be heated to such temperatures that it will change its geometry. Naturally, in this case, depressurization will also occur. This is especially true for iron-asbestos gaskets.

Another reason is the violation of the tightening torque of the bolts. Both very high and low torque values have a detrimental effect. In the first case, the gasket can be destroyed, especially if it is made of low-quality materials. And in the second — to let the exhaust gases to the outside, without preventing them. In this case, the gases together with the atmospheric air will have a detrimental effect on the gasket material, gradually putting it out of service. Ideally, the bolts should be tightened using a torque gauge, and the tightening sequence should be followed. Reference information on this can be found in the manual.

As a rule, the tightening sequence is that the center bolts are tightened first and then the others diagonally. At the same time, the tightening is done in stages.

According to statistics, 40% of all cases in which the gasket has failed, were caused by incorrect tightening torques or failure to follow the tightening sequence. In half of the cases, the gasket burned out due to engine overheating. Otherwise, it simply reached the end of its service life.

Also, sometimes the cause of the gasket is a problem with the combustion process (detonation, glow ignition). Because of overheating the cylinder head suffers a lot. Cracks can appear in it, which will also lead to depressurization of the described systems. The head is usually made of aluminum. And in the process of heating, it expands faster than the steel bolts. Therefore, the head starts to put a lot of pressure on the gasket, and the gasket is overloaded. This causes the gasket materials to harden, which in turn causes depressurization.

Often when the gasket fails, it burns through the rim or between the cylinders. This often results in erosion of the cylinder block surface and the bezel itself near the damage. Discoloration of the gasket material near the trim can also indicate high temperatures in the combustion chamber.

How to diagnose a cylinder head gasket leak

You can use one of several methods to tell if a cylinder-head gasket is leaking. To check the integrity of the head gasket, do one of the following:

How to check for a blown head gasket: video

  • With the engine running, visually inspect to see if smoke is coming from the gap between the cylinder-head gasket and the BC. Also, listen for loud ringing noises coming from there that were not there before.
  • Inspect the surfaces of the radiator cap and expansion tank of the cooling system, as well as the engine oil filler neck. To do this, simply unscrew them and visually inspect them. In case the antifreeze got into the engine, there will be a reddish emulsion on the oil filler cap. If the oil got into the antifreeze, there will be oily deposits on the radiator caps or expansion tank.
  • Make sure there is no white smoke coming out of the exhaust pipe (actually it is steam). If there is, there is a high probability that the gasket is burned out. Especially if the exhaust smoke has a sweetish smell (in case you use antifreeze instead of common water as a coolant). At the same time, usually the coolant level in the radiator drops. This is an indirect sign of the mentioned malfunction.
  • Check if there are any exhaust gases coming into the cooling system. This can be done in two ways — visually and with the help of improvised means. In the first case, it is enough to unscrew the radiator cap or expansion tank and see if there is intensive bubbling. However, even if intensive «geysers» are not observed there, it is necessary to use improvised means. More often a banal condom is used for this purpose.

There are two simplest and most effective ways, which will be suitable for diagnosing the fault when the exhaust gases break into the cooling system.

Checking the integrity of the gasket with a condom

Checking the integrity of the gasket with a condom

One of the effective and popular methods of checking is the method of using a balloon or condom. It is placed on the neck of the expansion tank by first unscrewing the cap. The main thing is to make sure that the condom sits tightly on the neck (you can use a bag or a balloon instead of a condom, but the diameter of the condom is usually perfect for the tank neck).

After you put it on the tank, you need to start the engine and let it run for a few minutes at 3,000 to 5,000 rpm. Depending on the level of depressurization, the condom will fill with gas quickly or slowly. It depends on the specific situation. In any case, if it started filling with exhaust gas, it means that the head gasket has been blown.

Checking the gasket with a bottle

Checking the gasket with a bottle

Another method to determine whether the cylinder-head gasket is blown, is often used on trucks. It is enough to have a small bottle of water (e.g. 0.5 liters). As a rule, the expansion tanks have a breather tube (a tube, by means of which the same pressure is maintained as the atmospheric pressure in a closed container).

When the engine is running, the end of the breather tube must be placed in a container with water. If the gasket is punctured, air bubbles will start to come out of the tube. If there are no bubbles, the gasket is OK. If coolant starts to come out of the breather plug, it also means that the gasket is OK.

Can I drive with a blown cylinder-head gasket? — It is possible, but undesirable, and only for short distances, in particular, to the garage or service center for repairs. Otherwise, the consequence of such a malfunction may be an engine repair.

How to Fix a Head Gasket Leak in Your Car

If you find out after a diagnosis that the gasket is leaking, there is nothing you can do about it except replace it. It is also worth inspecting the surrounding surfaces, and most importantly, try to find out the true cause of the blowout.

The price of the gasket may be different and depends on the car brand and the manufacturer of the part itself. However, in comparison with other assemblies, it is not high. Repair work may cost you somewhat more than simply buying a gasket. The cost of fixing the problem will depend on several things:

Checking a blown head gasket with no specialized tools: video

  • If in the process of dismantling the cylinder head cylinder head, it will be found out that the fixing bolts are «twisted» and they do not correspond to the technical parameters, they will have to be replaced. And sometimes there are situations when, due to changes in the geometry of the cylinder head, the bolt cannot be unscrewed and has to be simply ripped off. To carry out this unpleasant procedure, there is the appropriate equipment. Modern engines are often fitted with bolts that work at the limit of their fluidity. This means that after removing the cylinder head (to replace the gasket or for other reasons) it is necessary to buy and install similar new ones.
  • If the plane of the cylinder head is disturbed, it will be necessary to grind it. Special machines are used for this purpose, the work on which will also cost money. However, the working plane of the cylinder head «leads» not so often, but it is still worth checking this parameter. If the surface has undergone grinding, then a new gasket must be purchased, taking into account the thickness of the removed layer of metal.

Before replacing the gasket yourself, it is necessary to clean the head of fouling, scale, and pieces of the old gasket. Next, it is necessary to inspect its surface. A special measuring tool is used for this, usually a ruler. It is spent on the surface, revealing the presence of gaps. The size of gaps should not be more than 0,5… 1 mm. Otherwise, the head surface should be grinded or completely replaced with a new one.

Instead of a ruler, you can use a thick sheet of glass (for example, 5 mm thick). It is placed on top of the surface of the head and looks for possible air spots. To do this, you can lubricate the surface of the head with a little oil.

When replacing the gasket it is recommended to grease its surface with graphite grease. This will make it softer and easier for it to «find its» place on the head surface. It also makes it easier to remove when removing the gasket. The advantage of graphite grease, in this case, is that the graphite is not squeezed out during operation, turning into ash.

After the repair work, the car owner should monitor the behavior of the motor. Whether the above-mentioned malfunctions (white smoke from the exhaust pipe, emulsion or fat stains in the coolant, oil on the joint between the cylinder head and the cylinder-head, no engine overheating and so on) do not occur again. And immediately after replacement, do not operate the engine at maximum power. It is better to let the gasket «settle» and take its place.


  • What are the first signs of a blown head gasket?

    Common signs of a blown head gasket are: white smoke from exhaust, decrease of the coolant level without a trace of leakage, bubbles in the radiator, too high a temperature under the hood.

  • Can you drive with leaking head gasket?

    Theoretically, it's possible to drive the car with a blown head gasket from 1 day to 1 week. But there is a huge risk of full gasket failure and coolant dumping into your combustion chambers.

  • How much does it cost to repair a leaking head gasket?

    It costs from 1500 to 2000 $ to repair a leaking head gasket. You will spend approximately 700 $ on parts and the labor cost will be over 800 $.

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