How Do You Pressure Test a Cylinder Head?

When it comes to keeping a diesel engine running well, it is often said that cylinder heads are the most challenging components to deal with. That’s not just us saying that; scientists from around the world have studied the issue of cylinder head durability and come to the same conclusion: due to the high thermo-mechanical stresses involved, cylinder head design is challenging and material selection is of paramount importance. We won’t go any deeper into the science here, but the key takeaway is this: despite handling lots of pressure and stress, cylinder heads are not invincible. Cracks, internal leaks, or compromised seals can wreak havoc on engine efficiency and reliability. That’s where pressure testing comes in—a straightforward yet vital process to ensure your cylinder head is up to the task.

In this post, we’ll explore how to identify warning signs, understand the risks of ignoring them, and explain how to pressure test a cylinder head with confidence.

Signs a Cylinder Head Is Losing Pressure

A cylinder head that’s failing to maintain pressure won’t hide its problems for long. Here are a few warning signs:

1. Coolant Loss or Overheating: Leaks in water passages can lead to coolant loss and overheating, which are often the first indicators of trouble.
2. Excessive Oil Consumption: Internal leaks can cause oil to seep into areas it doesn’t belong, leading to excessive consumption or contamination.
3. White or Blue Exhaust Smoke: White smoke signals coolant entering the combustion chamber, while blue smoke points to burning oil—both of which can stem from cylinder head issues.
4. Decreased Engine Performance: Loss of compression, sluggish performance, or poor fuel economy could mean your cylinder head isn’t sealing properly.

If you’re noticing these symptoms, it’s time to dig deeper with a pressure test.

Potential Consequences of Ignoring the Warning Signs

Overlooking pressure-related issues in a cylinder head can lead to catastrophic engine failure. Small cracks or leaks often grow under continued pressure, damaging valve seats, the engine block, or even the pistons. Beyond that, overheating caused by coolant loss can warp the cylinder head itself, leading to costly repairs or replacements.

In short, ignoring these warning signs can turn a manageable repair into a full-blown engine rebuild.

How to Pressure Test a Cylinder Head

Pressure testing a cylinder head involves checking for leaks and cracks that aren’t always visible. Here’s how to do it step-by-step:

1. Remove the Cylinder Head
   Begin by removing the cylinder head from the engine block. Be methodical with head bolts, as incorrect removal can cause warping. Once removed, clean the surface thoroughly to eliminate grease, carbon deposits, or old gasket material.
2. Seal the Cylinder Head
   Use plates or covers to seal off the cylinder head’s intake, exhaust, and water passages. This ensures the pressure test is focused on the cylinder head itself.
3. Apply Pressure
   Using a cylinder head pressure tester, introduce compressed air into the head through the appropriate port. Most mechanics recommend applying pressure between 30–50 psi. Submerge the cylinder head in a tank of water during this step to spot air bubbles.
4. Inspect for Leaks
   Watch for air bubbles escaping from cracks, valve seats, or other critical areas. These bubbles indicate internal leaks that need addressing.
5. Conduct a Magnetic Particle Test (if applicable)
   For cracks too small to detect visually, consider a magnetic particle test. By applying a magnetic field and dusting the head with magnetic particles, tiny cracks become visible for further inspection.
6. Record and Evaluate Results
   If leaks or cracks are found, determine whether the head can be repaired or must be replaced. Minor issues may be repairable with welding or machining, but extensive damage often calls for a new cylinder head.

BehindThe8: Cylinder Heads You Can Trust

At BehindThe8, we understand the demands placed on diesel engines—and we know your cylinder head is at the heart of it all. That’s why we provide high-quality, heavy-duty cylinder heads designed for durability and performance.

With over 25 years of experience supplying diesel engine components, we’re committed to helping repair shops, fleet operators, and DIY mechanics find the parts they need to keep their engines running smoothly. Got questions? Check out our FAQs for quick answers or contact our team for personalized support.

When it comes to reliable replacement parts, BehindThe8 has you covered. Don’t settle for less—choose the parts that keep your engine running strong.