Is my cylinder head cracked?

Cylinder Head Parts

One of the most pivotal parts of any car is it's cylinder head. The cylinder head contains the primary parts of the combustion process that ultimately power the vehicle. 

The engine in each car contains four main components

• The Cylinder Head Cover
• The Cylinder Head
• The Engine Block
• The Oil Pan

The Cylinder head is mounted to the top of the engine block, with a series of long bolts travelling through the head and threading into the engine block. 

The Engine block containst the rest of the important components of the engine such as the crank case, the pistons, coolant and oil passages, rods and camshafts. 

Together the cylinder head and the engine block form the combusion chamber of the vehicle.

In Operation

Whilst the engine is running, all the parts are subject to huge mechanical and thermal stresses. Modern day engine blocks are typically made from cast alloyed iron or aluminium. Generally aluminium engine blocks are most popular with performance engines given their lower weight and their ability to handle higher heat and wear resistance. 

It's the cylinder head that closes the cylinder inside the engine block, creating the combustion chamber. The combustion chamber contains the fuel and air mixture, which is then ignited to create the power that pushes the piston down. The cylinder head, after letting in the combustion mixture, releases the exhaust gases out after the combustion has occured. 

This process is done many thousands of times per minute, which means the cylinder head material must be very strong. However, they're also required to be lightweight so that it can complete it's movement fast enough. Given the juxtaposition of requiring strength and light weight, typically cylinder head cracks happen every 5 to 7 years.

Cracking is an indication of the cylinder head experiencing more stress than it can handle.

There are an array of symptoms that indicate a crack in the cylinder head. 

Symptoms: 

Oil leak:

The cylinder head contains oil to not only lubricate, but also dissipate heat. If the ‘check oil’ engine lights up on the dashboard or there is oil under a parked vehicle where the engine is, these could be indicators of an oil leak caused by a cracked cylinder head.

Coolant leak:

Coolants are also in use to reduce the heat in the engine including the cylinder head. Typical indications of this issue besides a leak below the engine is the ‘check engine temperature’ lighting up if this is available on your vehicle dashboard.

Milky / yellow coloured engine oil:

This happens when the coolant passes through the pistons and mix with the engine oil resulting in a milky white colour. Utilising the dipstick to check the oil colour is an easy way to figure this out.

Poor engine performance:

Indicators of noticeable loss in engine power include the vehicle not accelerating properly when moving from a stop or struggling when driving uphill. A cracked cylinder head affects the engine performance with compressed air escaping from the combustion chamber.

Misfiring Engine:

As explained earlier the cylinder head closes to create pressure for combustion. The pressure created is impacted when the cylinder head cracks, leading to poor performance as above or even engine misfiring owing to no combustion. This is a serious issue that needs immediate investigation as unburnt fuel can impact other components of the engine.

Smoking engine:

Besides heavy pollution, a severely cracked cylinder head can release exhaust gases directly into and around the engine space and needs immediate replacement.

Needless to mention, it is far cheaper to have the cylinder head checked and repaired at an early than at a later stage when it has spread and even impacted other parts in the car. Most specialist engine repairers have cylinder head crack testing machines that make it easier to decide if it is more economical to repair or replace the part. Most cracks can be pinned or welded based on the cylinder head material.