How do you know if you've burned out your engine head? Symptoms, causes, tests, and costs (2025)

Updated November 2025 — by Gianni Tritella. The cylinder head is one of the most critical components of a combustion engine: it seals the top of the cylinders and controls compression, airflow, and coolant. When it becomes damaged—or “burned”—it can cause overheating, loss of power, white smoke, and oil contamination . In this guide, we explain how to recognize the symptoms, what tests to perform, and how much it costs to repair it in 2025.

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✅ What is the cylinder head and why can it "burn"?

The engine head is an essential part of the internal combustion engine: it closes the upper part of the cylinder block and houses the intake and exhaust valves , the injectors , the spark plugs (in petrol engines) or the diesel injectors , as well as a complex network of channels for cooling and lubrication .

Between the cylinder head and the engine block is a crucial component: the head gasket . Its job is to perfectly seal the engine, preventing the mixing of oil, coolant, and combustion gases . When this gasket loses its seal, a chain of problems begins that leads to a so-called "blown cylinder head."

🔥 Why the cylinder head can get damaged

The main cause is engine overheating . If the coolant drops below the minimum level or the fan fails to operate, the internal temperature can exceed 110–120°C . Under these conditions, the metal of the cylinder head (aluminum or cast iron) expands unevenly with respect to the engine block, causing deformations or micro-cracks.

A “burned” cylinder head doesn’t literally mean that it’s melted, but that the gasket or contact surface has failed : exhaust gases leak into the water passages and the oil becomes contaminated, causing symptoms such as white smoke, decreased performance and bubbles in the expansion tank .

⚙️ Materials and risk factors

• Aluminum engines → lighter but more sensitive to heat: they deform easily if the engine boils.
• Multilayer gaskets (MLS) → offer good sealing but require perfectly flat surfaces.
• Incorrect antifreeze → using unsuitable or mixed liquids can cause galvanic corrosion and damage the cooling channels.
• Lack of maintenance → delayed oil or coolant changes accelerate seal wear.

In short: the cylinder head doesn't "burn out" on its own, but is the result of a thermal imbalance or maintenance . A small amount of overheating, left untreated, can, over time, lead to a loss of compression and damage to the entire cylinder head.

🔍 Symptoms of a Burnt Cylinder Head

Early recognition of the symptoms of a damaged head gasket is crucial to avoid damaging the entire engine. Here are the most reliable signs, collected from workshops and real-world cases:

🚗 1. Loss of power and irregular operation

The engine loses compression in one or more cylinders: you notice a sharp drop in performance , vibrations at idle, and difficulty accelerating. Often the engine “ jumps, ” and the yellow engine light stays on with errors such as P0300–P0304 (multiple misfires).

🌡️ 2. Continuous overheating

The fluid level may appear normal, but the temperature quickly rises above 100°C or the fan remains constantly active. This is the most dangerous sign: an engine that continues to run hot risks permanent cylinder head deformation .

💧 3. Contaminated oil (“mayonnaise”)

When coolant enters the oil system , a whitish or foamy substance forms under the oil cap or on the dipstick. This compromises internal lubrication and accelerates engine bearing wear.

💨 4. White smoke from the exhaust

This is the most well-known symptom: the coolant entering the combustion chamber evaporates and produces a dense, persistent white smoke . If the smell is sweet (ethylene glycol), the diagnosis is almost certain.

🔥 5. Fluid leak without external traces

When the coolant level drops without visible leaks, it means it's being burned with the mixture or is escaping in gaseous form into the exhaust system. In these cases, the expansion tank often shows bubbles or abnormal pressure.

💨 6. Bubbles in the expansion vessel

During operation, continuous bubbles may be observed in the cooling circuit . This is the direct result of combustion gases seeping into the water channels: a classic sign of a punctured head gasket or a warped cylinder head.

⚠️ 7. Engine lights and error codes

The control unit may record DTCs for misfire, coolant temperature, or abnormal lambda sensor . The most common are:

• P0300–P0304 → cylinder misfire
• P0117 / P0118 → liquid temperature sensor out of range
• P0420 → reduced catalyst efficiency (due to the presence of water vapor in the exhaust gases)

🧠 Common causes of cylinder head failure

Cracks or deformations in the engine head almost always result from excessive overheating or a malfunction in the cooling circuit. In other cases, they are the result of assembly errors or worn components that compromise the gasket's seal.

• 🔥 Prolonged overheating – The most common cause. It can be caused by a coolant leak , a faulty fan, a clogged radiator, or a stuck thermostat. High temperatures distort the cylinder head surface and damage the gasket.
• ⚙️ Defective or poorly fitted head gasket – During an engine overhaul, if the surface is not perfectly flat or the tightening screws are not tightened to the required torque and sequence , the gasket may fail prematurely.
• 💧 Inefficient water pump – Reduced flow or damaged blades prevent proper fluid circulation, creating localized hot spots in the engine. In many cases, the damage begins near the fourth cylinder, the one furthest from the pump.
• 🧊 Incorrect or improperly mixed antifreeze – Using the wrong coolant (or mixing it with tap water) can cause galvanic corrosion and cavitation in the cylinder head passages, leading to pinholes or internal cracks. Always use antifreeze that meets OEM specifications (e.g., OAT or HOAT).
• ⚡ Irregular pressure in the circuit – A faulty expansion tank cap or a faulty temperature sensor can cause the circuit to work at abnormal pressures , accelerating the deformation or loss of seal of the gasket.
• 🪫 Ovalized cylinders or warped engine block – After severe overheating or seizure, the engine block can lose its perfect geometry. The cylinder head, even if reworked, can no longer seal uniformly, causing micro-leaks in compression and contamination.

🧪 Tests to diagnose a burned cylinder head

Before disassembling the engine, some diagnostic tests can be performed to confirm or exclude the problem:

1. CO₂ test in coolant – checks for the presence of exhaust gases in the cooling circuit.
2. Pressure test circuit – holds the system under pressure to see if it drops (indicates internal leakage).
3. Cylinder compression or leak test – measures the compression of each cylinder and identifies any abnormal differences.
4. Oil analysis – presence of glycol or water in engine oil.
5. OBD2 electronic diagnostics – checks for any DTCs related to misfires, temperature or catalytic converter inefficiency.

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💰 How much does it cost to repair a burned cylinder head (2025)

The cost varies depending on the type of engine, accessibility, and collateral damage (water pump, gasket, injectors, etc.).

💡 Prices vary depending on the car model, engine size, and spare parts availability. It's always advisable to request a quote including disassembly and cylinder head testing at a reconditioning shop.

🧯 How to prevent cylinder head failure

• Check the coolant level regularly and use only the prescribed coolant (never tap water).
• Check that the radiator fan starts correctly.
• Replace the reservoir cap gasket if it loses pressure.
• Change the coolant every 4–5 years to prevent internal corrosion.
• Do not continue to drive with the engine overheating : a few minutes are enough to damage the cylinder head.

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📌 Conclusions

A blown cylinder head isn't always a sudden failure: it's often the result of small, overlooked signs . Recognizing them early—white smoke, repeated overheating, bubbles in the circuit—can save you over €1,000 in expenses.

If you suspect damage, perform a pressure test or CO₂ test at your trusted workshop, or with certified instruments. Prompt intervention can save not only the cylinder head, but the entire engine.