How to Pressure Test a Cylinder Head? Cylinder Head Inspection

Cylinder Head Inspection

Cylinder head inspection helps to pinpoint the source of failure. This is the requirement before repairs, sometimes even before confirming replacement. During inspection, the head is checked for cracks, warping, and leaks. There are different ways to diagnose these issues, including doing a cylinder head pressure test. Learn about the methods in this chapter

Cylinder Head Inspection Methods

It’s usually difficult to fix a cylinder head problem whose existence you do not know of. That’s why diagnosis, or cylinder head inspection, precedes repair. Because the head gets damaged in different ways, there are several methods to check it. The most common are:

  • Cylinder Head Flatness Test
  • Magnetic Particle Method (wet and dry)
  • Dye Penetrant Method
  • Cylinder Head Pressure Testing
  • Vacuum Test

Each, method checks a specific cylinder head problem. Checking for flatness helps to detect warps. The magnetic particle and dye methods, on the other hand, examine the head cracks. A pressure test helps check for cracks and other openings.

Here is a more detailed look at the methods.

checking a cylinder head for flatness
checking a cylinder head for flatness

Flatness Cylinder Head Inspection

This is a simple way to detect a warped cylinder head. It also does not require rare tools or professional expertise. Basically, it involves using a flat edge and the blades of a feeler gauge.

To check for flatness, place the straight edge on the cylinder head deck. This is the side that faces the engine block. Then, slide the blade of the feeler gauge underneath the edge. A stuck blade indicates a warped surface.

Repeat the process while placing the straight edge longitudinally, diagonally, and across the surface of the head assembly. It’s also necessary to have with you the manufacturer specs for deck flatness.

Magnetic Particle Cylinder Head Inspection

This method checks for cracks in cast iron cylinder heads using a magnetic powder and magnetic field. The source of the magnetic field is usually either a permanent magnet or electromagnet. Upon applying a magnetic field, the particles along the cracks align themselves differently, thereby identifying the location of damage.

There are two different versions of the method: dry magnetic particles and wet magnetic particles. The dry method uses a dry powder while the wet method uses the particles in the form of a spray. The magnetic particles in the wet method are normally mixed with a fluorescent material for visibility and oil-based carrier to allow spraying.

The advantage of dry magnetic powder is that it does not create a mess, unlike the wet powder that requires cleaning after the test. However, cylinder head inspection using the wet magnetic particle method is more sensitive and can detect smaller cracks.

Dye Penetrant Cylinder Head Inspection

As the name suggests, this method uses dye to show cylinder head crack or pinhole locations. It’s commonly used on aluminum heads. These types of cylinder heads are not magnetic properties, which renders magnetic powder unusable.

The dye works by penetrating openings and making them visible to the eyes. Before using it, clean the cylinder head to rid it of dirt, grease, and carbon buildup. After that, apply the dye and let it soak for 15-20 minutes. You will then need to apply a developer and make the cracks and pinholes visible.

Cylinder head inspection dye may or may not require ultraviolet light to visualize. The dyes that work in ultraviolet light are more sensitive than those that use normal light. This method is one of the most cost-effective options. You can use it where magnetic particles will not work, such as inspecting aluminum heads.

cylinder head leak test
cylinder head leak test

How to Pressure Test a Cylinder Head

A cylinder head pressure test, as the name implies, means using pressure to diagnose the assembly. Pressure testing helps to detect cracks and pinholes. You can use it alongside the methods above or after cylinder head repairs. There are also two different methods for the test, as explained next.

A cylinder head pressure test can use the wet or dry method. In the wet method, the head is completely submerged in the water. In the dry method, you spray the cylinder head with water instead.

In all these methods, you need to start by cleaning the cylinder head. This will help remove dirt, grease, and carbon, so the test can reveal cracks and holes within the assembly. Next, seal the water passageways using a block off plate.

The next step in cylinder head pressure testing involves using compressed air to apply pressure of around 20-30 psi. In the wet method, this is done with the head completely in water. Bubbles will then escape to indicate the presence of cracks or openings.

In the dry method, you do not submerge the head. Instead, spray it with a soapy water solution. This will make bubbles to form if the assembly is cracked. It’s good to note that the cracks revealed when using this method are those that connect to the water passages.

Cylinder Head Vacuum Test

Another common method when inspecting cylinder head problems is the vacuum test. This test commonly measures the condition of valve seats. Basically, you’re testing them for damage that causes the valves to leak. Cylinder head valve seats often go bad when they wear out over time, or due to overheating.

During the cylinder valve leak test, the water passages are closed by plugging them. You also need a vacuum pump to help you determine if there’s a pressure drop due to cracks. After closing off the water ports, pump out 25 Hg of vacuum and observe the reading.

A vacuum drop of the vacuum then indicates the presence of cracks within the assembly. Note that this method, unlike the others mentioned before, will not help you locate the cracks. This is its main drawback.


Cylinder head inspection involves several processes. In addition to a physical examination, you can use the methods explained in this section. Some require special tools, while others are easy to perform. After finding the source of failure, you can choose to either repair a cylinder head or replace it. The next part is aimed at those who choose repair. Read it for information regarding when to do it and the methods available.


I'm Louis, a seasoned writer specializing in auto parts, particularly the science behind components like cylinder heads and pistons. With over a decade of experience and a background in mechanical engineering, my articles reflect a commitment to professionalism, blending technical insight with engaging content.

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