Is My Cylinder Head Cracked?

The cylinder head is a key part of the internal combustion engine and critical in powering a vehicle. The engine has four main components; the cylinder head cover, the cylinder head, the engine block and the oil pan. Mounted on top of the engine block, the cylinder head is fixed with long bolts that pass through the cylinder head and thread into the engine block. The engine block has other important components such as the crank case, piston, coolant and oil passageways, connecting rod, camshaft, etc. Together with the cylinder head, the engine block forms the combustion chamber of the vehicle.

When the engine is running, it is subjected to heavy mechanical and thermal stress. Most engine blocks are manufactured from cast alloyed iron. Aluminium engine blocks are however popular for performance engines owing to the lower weight for better handling, higher thermal resistance and better wear resistance.

The cylinder head closes the cylinder containing the fuel and air mixture for combustion and then opens to release the exhaust gases. This is done thousands of time per minute and hence the cylinder head is made of tough materials. In saying that, it is also required to be lightweight enough to complete its movements fast enough. Owing to this balance being required to be maintained, typically cylinder head cracks occur in 5 – 7 years.

Cracking is an indication of the cylinder head experiencing more stress than it can handle. So, what are obvious symptoms of a cracked cylinder head? Few of the symptoms are:

• 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. Specialised engine repairers like Engine Specialists 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.