Spark plug iridium and platinum for car

What are spark plugs?

A spark plug is a component of the ignition system in a petrol engine, responsible for igniting the air–fuel mixture in the combustion chamber. The plug generates an electrical spark at a voltage of 20,000–40,000 volts, which ignites the mixture of petrol and air at a precisely defined moment in the engine's operating cycle. It is a consumable part, and its condition directly affects engine power, fuel consumption, and ease of starting. Important: Diesel engines do not use spark plugs — they use glow plugs instead.

Spark plug construction

The main components of a spark plug:

• Centre electrode. A conductor made from a nickel alloy, platinum, or iridium, through which the high-voltage current is supplied. Diameter: 0.4–2.5 mm, depending on the type of plug.
• Side electrode (earth electrode). A bent metal element welded to the shell. The spark jumps between the centre electrode and the side electrode.
• Ceramic insulator. A high-strength insulator made from aluminium oxide (Al₂O₃), capable of withstanding temperatures of up to 1,000 °C. It prevents current leakage and ensures heat dissipation.
• Metal shell. A threaded steel casing (M10, M12, M14, or M18) for screwing into the cylinder head. It provides earthing and a gas-tight seal.
• Sealing washer. A metal crush washer (typically folded steel) that seals the connection between the plug and the cylinder head.
• Contact terminal. The upper part of the plug for connecting the high-tension lead or ignition coil.

The key parameter is the heat range: it determines the plug's ability to dissipate heat.

• “Cold” plugs are suitable for high-performance turbocharged engines and motorway driving.
• “Hot” plugs are ideal for small-displacement engines and urban driving. Always use the heat range specified by your vehicle's manufacturer.

How it works

The process of igniting the air–fuel mixture takes place in fractions of a second:

1. The engine control unit (ECU) determines the ignition timing based on sensor data.
2. The ignition coil converts the vehicle's supply voltage (12 V) into a high-voltage pulse (20,000–40,000 V).
3. The pulse is delivered to the centre electrode of the plug.
4. A spark jumps between the centre and side electrodes across the spark gap (0.7–1.1 mm).
5. The spark ignites the air–fuel mixture in the combustion chamber.
6. Controlled combustion occurs, creating pressure on the piston.

At 3,000 rpm each plug produces 25 sparks per second, and over 100,000 km — more than 100 million sparks. These demands explain why the electrodes gradually wear out and why plugs require replacement.

Types of spark plugs

While specialised materials like silver or ruthenium exist for specific applications, the vast majority of modern passenger cars use one of three main types. These most common spark plugs differ primarily in their electrode material, service life, and price. The choice of type depends on the engine's requirements, driving style, and budget.

Nickel (standard) spark plugs

The classic and most affordable type, with a nickel centre electrode of 2.0–2.5 mm diameter.

Specifications:

• Electrode material: nickel alloy (Ni-Cr)
• Centre electrode diameter: 2.0–2.5 mm
• Service life: 20,000–30,000 km
• Price: 3–8 EUR per plug

Advantages:

• Low cost
• Broad compatibility with many older or standard naturally aspirated petrol engines
• Suitable for older vehicles without complex ignition systems

Disadvantages:

• Rapid electrode wear — frequent replacement required
• Less stable spark under high load
• Higher fuel consumption compared with iridium and platinum plugs

Recommended for: Older vehicles, low-mileage engines, cost-conscious use.

Platinum spark plugs

Standard platinum plugs feature a fine platinum tip (0.6–1.1 mm diameter) on the centre electrode only. Double platinum plugs, however, feature this same platinum tip on the centre electrode, alongside an additional platinum pad welded to the side electrode.

Specifications:

• Electrode material: platinum tip on a nickel base
• Centre electrode diameter: 0.6–1.1 mm
• Service life: 60,000–80,000 km
• Price: 8–18 EUR per plug

Advantages:

• Last 2–3 times longer than nickel plugs
• Stable spark throughout the service life
• Resistance to erosion and carbon fouling
• Double platinum is recommended for engines with a waste spark distributorless ignition system (DIS)

Disadvantages:

• 2–3 times more expensive than nickel plugs
• Inferior to iridium plugs in terms of service life and spark stability

Recommended for: Modern petrol engines, mid-range vehicles, LPG installations.

Iridium spark plugs

The most modern type of spark plug, featuring an ultra-fine iridium electrode. Iridium is one of the hardest and most heat-resistant metals, providing maximum service life and spark quality.

Specifications:

• Electrode material: iridium alloy
• Centre electrode diameter: 0.4–0.7 mm (the finest of all types)
• Service life: 80,000–120,000 km
• Price: 12–30 EUR per plug

Advantages:

• Maximum service life — up to 120,000 km
• The finest electrode produces the most concentrated spark
• Improved ignition of lean mixtures
• Reduction in fuel consumption of 1–3%
• Stable operation at high temperatures (up to 2,450 °C — the melting point of iridium)
• Reduction in CO₂ emissions

Disadvantages:

• High cost — 3–5 times more expensive than nickel plugs
• Fragile if fitted incorrectly (the gap must not be adjusted manually)
• Minimal benefit for older engines

Recommended for: Modern turbocharged engines (TSI, TFSI, EcoBoost), direct injection vehicles, performance driving.

Comparison table of spark plug types

The table below compares the main types of spark plug by key specification.

Spark gap and tightening torque

Two parameters that are critically important when fitting spark plugs are the spark gap and the tightening torque. Incorrect values lead to unstable engine operation or damage to the cylinder head.

Spark gap

The distance between the centre and side electrodes across which the spark jumps. The standard gap for most vehicles is 0.7–1.1 mm. The exact value is specified in the vehicle owner's manual.

• A gap that is too small produces a weak spark, incomplete combustion, and power loss.
• A gap that is too large causes misfires, difficult starting, and excessive load on the ignition coil.

Important: Iridium and platinum plugs are supplied with the gap set at the factory — do not adjust the gap manually, as this will damage the fine electrode tip.

Tightening torque

The correct tightening torque is an essential requirement during fitting. Under-tightening leads to a loss of seal and overheating; over-tightening damages the thread in the cylinder head (repair cost: 200–800 EUR).

Spark plug socket size: For M14 plugs, use a 16 mm or 21 mm socket depending on the model. For compact plugs with a slim body (modern turbocharged engines) — a 14 mm socket. Always check the manufacturer's specification.

It is recommended to use a torque wrench for accurate tightening. If one is not available, check the packaging of your specific spark plug brand for the tightening angle. For a new M14 plug with a washer, Bosch typically recommends a 90° turn, while NGK and Denso recommend a 180°–240° turn after the plug is finger-tight.

These values are reference ranges for common sizes. Actual torque may vary by design; always prioritise the exact specifications provided by the vehicle or spark plug manufacturer.

Important Note on Reinstallation: For a previously used gasket-seat spark plug, do not assume the same angle-tightening rule as for a new plug. Many manufacturers recommend replacing the plug, or at minimum replacing the gasket where applicable because a crushed sealing washer may no longer seal correctly. Always follow the vehicle or spark plug manufacturer’s torque specification.

Service life and replacement intervals

The replacement interval for spark plugs depends on the type of plug, the engine, and operating conditions. Vehicle manufacturers specify the replacement interval in the service book; however, the actual service life may differ.

Replacement intervals by plug type

The table below shows average spark plug service life figures depending on type and operating conditions.

Note on Double Platinum: Even with optimal motorway driving, do not exceed 100,000 km. Beyond this point, the metal threads risk seizing in the cylinder head, and the ceramic insulator may become brittle. For safe service life beyond 100,000 km, iridium plugs are required due to their specialized anti-corrosive plating.

Factors affecting service life

The actual service life of spark plugs depends on many variables:

• Driving style. Aggressive driving at high engine speeds reduces service life by 20–30%.
• Urban driving. Frequent starts and short journeys accelerate carbon fouling.
• Engine condition. Excessive oil consumption contaminates the plugs, shortening their service life.
• Fuel quality. Poor-quality petrol increases carbon build-up.
• LPG/CNG installations. Higher combustion temperatures reduce service life by 30–50%. Specialist plugs are recommended for gas installations (NGK LPG LaserLine, Denso Iridium Tough).
• Engine type. Turbocharged engines (TSI, TFSI) impose greater demands on spark plugs.

Signs of spark plug failure

Worn or defective spark plugs produce characteristic symptoms that a driver may notice during everyday use. Identifying the problem at an early stage means avoiding costly repairs to ignition coils and the catalytic converter.

Symptoms of defective plugs when driving

• Difficult starting. The engine cranks for a long time, particularly in cold weather. In severe cases, the vehicle will not start.
• Rough idle. The engine misfires — running unevenly and with vibration.
• Hesitation on acceleration. The vehicle judders when the accelerator is pressed, particularly during acceleration at low engine speeds.
• Loss of power. The engine feels noticeably sluggish and acceleration is reduced.
• Increased fuel consumption. Incomplete combustion increases petrol consumption by 10–20%.
• Check Engine warning light. Misfires may trigger fault codes such as P0300 or cylinder-specific codes such as P0301–P0304.
• Popping from the exhaust. Unburnt fuel ignites in the exhaust manifold.

Diagnosis by visual inspection of the plug

The appearance of a removed spark plug is a valuable diagnostic tool. The colour and condition of the electrodes indicate the engine's operating mode.

Replacing spark plugs

While replacing spark plugs is a manageable DIY task for most inline engines, vehicles with restricted access (such as V6, V8, or horizontally opposed/boxer engines) may require professional workshop assistance.

To perform the replacement, you will need a spark plug socket (14, 16, or 21 mm) with an extension bar and ratchet, a torque wrench for precise tightening, compressed air, and dielectric grease.

Spark plug replacement procedure

Preparation:

1. Switch off the ignition and allow the engine to cool completely. Plugs must be changed on a cold engine to prevent stripping the threads in the aluminium cylinder head.
2. On vehicles with sensitive electronics, disconnect the negative battery terminal.

Removal:

1. Disconnect the ignition coil connector (or high-tension lead). Always pull by the connector/boot, never by the wire.
2. Remove the ignition coil from the plug well.
3. Blow out the open plug well with compressed air.
4. Fit the spark plug socket onto the plug and unscrew it anti-clockwise.
5. Remove the plug and inspect the electrodes and insulator to assess engine condition.

Installation:

1. Verify the new plug — the type, heat range, and gap must match the vehicle's specification.
2. Thread the new plug in by hand until it seats against the cylinder head — this prevents cross-threading.
3. Tighten the plug to the specified torque with a torque wrench.
4. Apply a small amount of dielectric grease to the inside of the rubber ignition coil boot (not the metal terminal) to prevent moisture and sticking.
5. Refit the ignition coil and reconnect the connector.
6. Repeat for all cylinders.

After replacement: Start the engine and check for a stable idle and the absence of any Check Engine fault codes. For the first 50–100 km, avoid maximum loads.

Important: If a spark plug is difficult to remove, do not use excessive force, as this may damage the threads. Follow the repair procedure for seized plugs specified by the vehicle manufacturer. Before installing the new spark plug, ensure that the threads and the threaded hole are clean and free of oil or lubricant, as lubricated threads can lead to incorrect torque and overtightening.

Spark plug prices in Germany

Spark plug prices vary according to type, brand, and vehicle model. On the German market, the cost of a set of plugs and the labour for replacement depend on several factors.

Prices by plug type

Current spark plug prices on the German market in 2026. Prices shown are per plug.

Workshop replacement costs

The total replacement cost consists of the price of the plugs plus labour. Labour time: 20–45 minutes for inline four-cylinder engines; 1–2 hours for V6/V8 or engines with restricted access.

Factors affecting cost: number of cylinders, plug type (nickel vs. iridium), access to plug wells, whether the inlet manifold or other components need to be removed, region of Germany.

Leading spark plug manufacturers

• For a budget-friendly and reliable option: Bosch, Champion, BERU — affordable price, proven quality for most engines.
• For maximum service life: NGK Laser Iridium, Denso Iridium TT — up to 120,000 km; optimal for modern turbocharged engines.
• For LPG/CNG vehicles: NGK LPG LaserLine, Brisk LPG, Denso Iridium Tough — resistant to elevated combustion temperatures.
• For performance driving: NGK Racing, Denso Iridium Racing — maximum performance, but shorter service life.

OEM vs. Original for spark plugs

Tip: Most “original” spark plugs from VW, BMW, and Mercedes are manufactured in NGK, Bosch, or BERU factories. Purchasing OEM plugs from the same brands means identical quality at a lower price.

Can spark plugs be cleaned?

Cleaning spark plugs is a debated topic. While it can temporarily restore performance, it is never a substitute for replacement, especially in modern high-compression engines.

When cleaning is acceptable:

• The electrodes show no physical wear, but are covered in dry carbon (soot).
• The vehicle has been sitting for a long time and the plugs have “wet-fouled” from failed start attempts.
• As a temporary measure until new plugs can be purchased.

Cleaning methods:

• Brass wire brush. Suitable for standard nickel plugs only. Gently remove soot without applying heavy pressure to the centre electrode.
• Ultrasonic bath. The most effective professional method; it removes deposits from the deep gaps without mechanical damage.
• Propane torch. Briefly heating the tip can burn off “wet” fuel fouling. (Note: Avoid overheating the ceramic insulator to prevent cracking).

Important limitations:

• Do not treat cleaning as a substitute for replacing a worn spark plug.
• Do not use abrasive methods on iridium or platinum plugs because their fine electrodes can be damaged easily.
• If the plug shows electrode wear, cracking, melting, or heavy deposits, replace it.

Recommendation: If a spark plug is worn or near the end of its service life, replacement is usually the better choice. For example, DENSO recommends replacement of standard nickel spark plugs in passenger cars at around 15,000–20,000 km, and NGK notes that cleaned plugs will not perform like new ones.

How to choose the right spark plugs

Selecting the correct plugs is the key to stable engine operation and a long service life. Choosing incorrectly leads to misfires, power loss, and even damage to the catalytic converter.

Step 1: Determine the base specification

The most reliable method is to use the vehicle manufacturer’s specification. The correct spark plugs can then be identified by vehicle application, OE part number, or VIN / Frame No. where supported in manufacturer or retailer catalogues.

• Thread diameter: for example M10, M12, M14, or other sizes
• Thread reach: 19 mm, 26.5 mm, or other values
• Heat range: stated in the service book
• Spark gap: must match the specific engine specification
• Socket size: common sizes are 14, 16, and 21 mm

Plugs can be selected by vehicle application or OE part number, and by VIN/Frame No. where supported. Selection by vehicle key number (Schlüsselnummer) through retailer catalogues is also possible.

Step 2: Choose by operating conditions

Once the correct physical fitment is established, you can choose the electrode material based on your driving habits to optimize performance and service life.

The golden rule: Always replace all spark plugs at the same time — fitting plugs with differing degrees of wear leads to uneven cylinder operation, vibration, and misfires.

Legislation and vehicle inspection in Germany

Spark plugs are not a specific inspection item at the TÜV; however, their condition directly affects parameters that are checked during the roadworthiness inspection.

Requirements for the vehicle inspection (HU/TÜV)

During the Hauptuntersuchung, carried out every 2 years, the following parameters related to the ignition system are checked:

• Emissions (Abgasuntersuchung, AU). Worn spark plugs can lead to incomplete combustion, which may increase CO (carbon monoxide) and HC (hydrocarbon) emissions and may cause the vehicle to fail the AU if the measured values exceed the permitted limits.
• Idle stability. Rough running or unstable idling can indicate misfires or combustion faults and may negatively affect the inspection result if they are linked to emissions-related defects.
• Check Engine Light (OBD). An active Check Engine Light or relevant OBD fault in the engine-management system can prevent the vehicle from passing the inspection. Misfire-related faults such as P0300–P0304 may be relevant where they affect the emissions system or engine management.

Environmental standards

Under German road-traffic regulations and current emissions standards, the vehicle’s emissions-control system must function correctly. Ignoring a faulty spark plug is therefore not only a performance issue, but may also lead to increased emissions and damage to exhaust-system components over time.

• HU/AU failure: Excessively high CO (carbon monoxide) and HC (hydrocarbon) levels can cause the vehicle to fail the emissions test.
• Catalytic converter damage: Persistent misfires can allow unburnt fuel to enter the exhaust system, which may overheat and damage the catalytic converter.
• Lambda sensor contamination: Long-term rich running or incomplete combustion can contaminate the oxygen sensor and impair mixture control.

Consequences and liability

Recommendation: Replace spark plugs in good time before the TÜV inspection. This prevents problems with emissions and ensures stable engine operation during the test.

Frequently asked questions (FAQ)