Replacing a cylinder head gasket: when it needs to happen and how to do it

16 February 2023

The head gasket is an essential component of your engine. It enables the engine’s cylinders to work together to power the machine forward. If the head gasket is malfunctioning, the problem needs to be rectified as quickly as possible. The longer you wait to fix it, the more damage you will have to repair. In this article, you will learn when, why and how to replace your engine’s cylinder head gasket.

What is a cylinder head gasket?

The head gasket is one of the most important gaskets in the engine. It seals the passages between the engine block and the cylinder head, enabling oil and coolant to circulate in the engine without leaking into the cylinders or outside the engine. The head gasket also acts as a force transmission element, influencing the distribution of the force being generated by the cylinders.

The high combustion power of modern engines means the head gasket must be strong enough to withstand very high temperatures and pressures. In the past, head gaskets were often made of copper or composite materials that typically contained graphite. Today, most head gaskets are made of multi-layer steel (MLS), which consists of two to five layers of thin steel coated in rubber.

Even though head gaskets are pretty tough these days, they are still subject to wear and tear. If something goes wrong with your head gasket, oil and coolant can leak into parts of the engine where they don’t belong, compromising safety and causing costly damage. That’s why a leaking head gasket needs to be replaced as soon as possible

How can you tell if your head gasket is leaking?

A broken cylinder head gasket, often called a blown head gasket, can cause a variety of engine issues. It’s important to know the symptoms that indicate your head gasket is leaking in order to remedy the issue promptly and limit your machine’s downtime.

The signs to watch out for include:

  • Overheating engine. When the seal of the head gasket is blown, it can leak coolant, which means the engine isn’t able to cool down like it needs to.
  • Low coolant level without any obvious leakage. The engine might be leaking coolant into the cylinders in the engine block.
  • Bubbles in the radiator or cooling reservoir. These are caused by gases from the combustion chamber escaping into the cooling system.
  • Loss of power. If the head gasket is perforated, it causes a loss of pressure in the combustion chamber and the engine power decreases.
  • White exhaust smoke. Coolant that flows into the combustion chamber burns and releases white smoke.
  • Milky engine oil. If a head gasket failure causes coolant to leak into the oil return passages, the engine oil can take on a milky appearance.
  • External leaks. Fluid leaking from the engine might be coolant or oil that’s escaped through a crack in the head gasket.

Why is it important to replace a blown head gasket?

The main dangers of operating an engine with a blown head gasket include:

  • Overheating. If your engine is losing coolant through a leaking head gasket, it’s likely to overheat and incur further damage.
  • Irreparable damage. When motor oil mixes with coolant, it becomes diluted and isn’t able to offer the necessary level of lubrication, which can lead to engine damage that’s impossible to fix.

How to replace a blown head gasket

The following is a general guide to replacing the head gasket in an engine. It is recommended that you also consult your machine’s manual for information that is specific to your engine.

  1. Remove the old head gasket.
  2. Clean the surfaces. Remove any rust or debris from surfaces that will be in contact with your new head gasket. Use an industrial cleaning product if necessary. The smoothness of the cylinder head and engine block surfaces has a significant impact on the performance of the head gasket.
  3. Check the components for unevenness and distortions. This can be determined by using a straightedge and the light-gap method. Place the straightedge testing device over the surface and view them together against a light source. Move the tool over the bolt holes from side to side and up and down. Any unevenness is made visible by light shining through the gaps. 
  4. Carefully position the new head gasket. Fit it perfectly over each cylinder bore by lining up its features with those on the engine block and pressing down evenly until it is seated in place. If necessary, wiggle the head gasket slightly as you’re pressing to ensure all the corners and side edges are fitted against their matching surfaces — but don’t force anything! When it’s lined up properly, the head gasket will fit into place easily. If something doesn’t seem right, check that you have the right part for your machine and/or check again for unevenness or distortions.
  5. Install new bolts. Screw the bolts down evenly until you have a snug fit, but be very careful not to over-torque them. Ensuring you have the proper selection of bolts and applying the correct tightening procedure play vital roles in achieving the necessary seal. That’s why it’s important to always follow the manufacturer’s instructions. In some engines, when the cylinder head gasket has been replaced, the cylinder head needs to be retightened after approximately 50 hours of engine use. Consult your service manual for specific instructions for your engine.

Ready to replace your cylinder head gasket?

At BEPCO, we offer a range of cylinder head gaskets suitable for the engines in a variety of machines. We also offer tools and accessories that can help, such as industrial cleaning products or a torque wrench. Browse our range to find the right part and tools for your engine, or contact us for more information.