Cracked Cylinder Head: Signs, Symptoms, and Replacement Cost

The cylinder head is a vital component of your engine’s functionality. It forms the top of the combustion chamber, sealing it off from the outside world, allowing fresh air into the chamber, and allowing exhaust gasses to exit.

If the cylinder head is cracked, things like poor engine performance, oil leaks, coolant leaks, visible smoke, misfires, and even total engine failure could occur.

What Is a Cylinder Head?

cylinder head

The cylinder head is the part of the engine that sits on top of the engine block and seals the combustion chamber at the top. The head gasket separates the block from the cylinder head, and the cylinder head contains the vehicle’s valvetrain. 

Its primary responsibility is to help maintain proper combustion within the engine, but since it also contains the valvetrain, it is also indirectly responsible for allowing the proper circulation of air into and out of the combustion chamber. 

Common Signs and Symptoms of a Cracked Cylinder Head

Because the cylinder head performs such vital functions, any one of these observed signs and symptoms should be taken seriously; Prolonged ignorance of any one of these issues could result in costly repairs or even complete engine replacement.

Additionally, it should be noted that because your vehicle’s cylinder head is a component directly related to engine performance, regardless of how much performance it makes at baseline, there are generally fewer signs and symptoms than other components that operate further “down the line.”

This should warrant an even greater urgency to address any issues that start to occur since any one of them can signal a great amount of damage that has already occurred within your vehicle’s engine. 

Poor Engine Performance

Probably one of the lesser issues a cracked cylinder head can pose is to make your engine performance suffer. It could do so in the form of rough idling, poor acceleration, engine hesitation, or overall lack of power. Depending on where the crack is, it could be the direct cause – causing a lack of engine compression – or an indirect cause – creating issues for the spark plugs and valves – of poor engine performance. 

Oil Leaks

Oil is used engine-wide for the lubrication of multiple components and parts. This includes the valves, and oil flows through the cylinder head to travel where it needs to be. A crack can cause oil to leak both into the internal parts of the engine and out onto the floor. 

An interior leak will cause issues like fouled spark plugs, oil burning, and eventually, engine misfiring as a result. External leaking can cause oil to drip onto hot parts of the engine and either smoke or catch fire. Depending on how large the leak is, a puddle could become visible on the floor, but if neither of these happens, your vehicle could be affected by low oil levels, causing issues of its own.

Learn More: Symptoms of Too Much Oil in an Engine

Coolant Leaks

Like oil, coolant also flows through the cylinder head and to various engine components to prevent overheating. A cracked head can cause basically the same issues as an oil leak, including the mixing of coolant and oil. When this happens, it has the potential to destroy engine components since the coolant is not designed to be a lubricant. Overheating can occur, burning coolant through the exhaust, and fouled spark plugs are the most common results. 

Engine Misfiring

As noted above, engine misfiring usually occurs as a result of some type of leak. Leaking can dump oil into the cylinder and foul up the spark plugs, causing the air and fuel mixture within the combustion chamber to fail to ignite. Misfiring can also occur when the compression levels drop too low. Normally, if a cracked head is bad enough to affect compression, there will also usually be some kind of oil or coolant leak.

Visible Smoke

There are two ways in which smoke can signal a cracked cylinder head. The first of which is again, the result of an oil leak into the combustion chamber, causing the burning of oil and visible blue smoke out of the tailpipe. 

The second form of smoke comes from the cylinder head itself. Exhaust gases can escape from the cylinder head through the exhaust valve even before it reaches the exhaust manifold if the head is not completely sealed. This could also happen if oil is dripping on hot surfaces of the engine.

Engine Failure

The worst-case scenario - that usually comes into play after ignoring the symptoms of a cracked cylinder head - is total engine failure. This usually occurs if a misfire develops and becomes worse or if continued normal use causes a small crack to become larger. 

What is the Expected Lifetime of a Cylinder Head?

old cylinder head

Cylinder heads themselves are usually meant to last the lifetime of the vehicle. Most new vehicles have aluminum cylinder heads, though some older cars have iron heads. It is more common that the valves or gaskets closely linked to or embedded within the cylinder heads fail first. 

The most common cause of premature cylinder head gasket cracking issues with the cooling system of a vehicle. Engine overheating combined with already high pressures within the combustion chamber can work to push the head past the limits with which it was designed, causing it to crack. Other cooling systems issues like air in the cooling system, coolant leaks, and water pump failure can lead to overheating and cracking.

Learn More: Signs and Symptoms of a Bad Radiator

How Much Does a Cylinder Head Cost to Replace?

Cylinder heads are not as expensive as one might think. Rather, it is the potential labor costs that can push a cylinder head replacement to higher costs. Parts usually cost anywhere from $200 to $500. Labor costs vary greatly depending on the make and model of your vehicle. 

Vehicles like BMWs, Audis, and other luxury cars often have various components that need to be removed to get to the cylinder heads. Subarus’ cylinder heads are notoriously hard to replace because of the boxer engine design. These factors increase labor time and cost, potentially pushing a cylinder head replacement to over $1000. Vehicles that have simpler, easier-to-access engines can cost as little as $400 to $500.

Final Thoughts

Cylinder heads are an important part of your vehicle’s engine. They contain the valvetrain and affix to the top of the engine block, ensuring complete sealing of the combustion chamber.

When a cylinder head becomes cracked your engine could suffer in the performance department, start to misfire, exhibit oil leaks, or start leaking coolant. All these signs should be heeded, and you should take your vehicle to a local mechanic immediately to avoid potentially long-term engine damage.

Richard Reed
I've been a General Manager of a moving company and I've also been a Professional Mover for over 30 years. I've driven flat beds, reefers, dropdecks, moving vans, heavy machinery, etc. In my time as a Mover I've driven over 1,000,000 safe miles. My days of moving and driving truck are past me but The Vehicle Lab allows me to share the knowledge I've gained over the past 40 years.
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