What types of spark plugs are there for a car: a complete guide to types and selection

Spark plugs are the “heart” of a gasoline engine, on which not only engine starting, but also its power, efficiency and even environmental friendliness depend. It would seem that it could be simpler: I bought them in a store that were the right size, screwed them in, and everything was in order. But in practice, choosing candles turns into a real quest: iridium or platinum, with what heat number, for gas or gasoline, original or analogue? A mistake in selection is costly: from increased fuel consumption to detonation and piston burnout.

In this article we will look at everything types of spark plugs, their design features and materials of manufacture. You will learn how to choose the right spark plugs according to the make of the car, which ones are best for gas (LPG), and which ones are best for forced engines. And also - myths about “eternal” candles, signs of wear and compatibility chart for popular brands. Without hype and marketing slogans - only technical facts and the experience of auto mechanics.

1. Spark plug design: what it consists of and how it works

Before we talk about the types, let's figure out how the spark plug works and why its parameters are so critical for the engine. Main elements:

• 🔥 Central electrode - “plus”, to which high voltage is applied (up to 40,000 V). The material and shape of the electrode determine the life and efficiency of the spark.
• 🔌 Side electrode (“ground”) - grounded to the housing. A spark jumps between it and the central electrode.
• 🧲 Isolator — ceramic case that protects against breakdown. The quality of ceramics affects heat transfer.
• 🔩 Metal body — threaded part for screwing into the cylinder head. Has a hex key.
• 📏 O-ring — prevents the breakthrough of gases from the combustion chamber.

The operating principle is simple: the ignition coil generates a high-voltage pulse, which, through tip supplied to the central electrode. A spark is formed between the electrodes, igniting the air-fuel mixture. But the devil is in the details:

• 🔥 Spark temperature reaches 2500–3000°C, but the candle must remain cold so as not to cause glow ignition (self-ignition of the mixture from a hot electrode).
• ⚡ Breakdown voltage depends on the gap between the electrodes. The larger it is, the more powerful the spark, but also the higher the load on the coil.
• ⏳ Candle life determined by the material of the electrodes. Regular nickel serve 30–50 thousand km, and iridium - up to 120 thousand km.

2. Types of spark plugs according to electrode material

The main difference between spark plugs is the material of the central and side electrodes. Depend on him resource, price and efficiency. Let's look at all the options from budget to premium.

2.1. Classic nickel candles

The most common and cheapest option. The central electrode is made of nickel alloy with the addition of manganese or chromium to improve corrosion resistance. The side electrode is usually steel.

• ✅ Pros:
  • Low price (from 100–300 rub. per piece).
  • Wide range for any car.
  • Easy to find in any store.
• ❌ Cons:
  • Small resource: 20–30 thousand km (even less on gas).
  • High breakdown voltage - load on the ignition coil.
  • Prone to electrode erosion and soot formation.

🔹 Who is it suitable for: owners of old cars (before the 2000s), those who drive little and do not want to overpay. Not recommended for modern engines with direct injection or a turbine.

2.2. Platinum candles

In these spark plugs, the central (and sometimes side) electrode has platinum coating thick 0.3–0.7 mm. Platinum is resistant to high temperatures and corrosion, so the service life increases to 80–100 thousand km.

• ✅ Pros:
  • Long service life (3–4 times longer than nickel).
  • Stable spark even under high loads.
  • Less soot and deposits.
• ❌ Cons:
  • The price is 2–3 times higher than nickel (from 500–1500 rub.).
  • Sensitive to fuel quality (with poor gasoline, platinum “burns out” faster).

🔹 Who is it suitable for: modern naturally aspirated and turbocharged engines, cars with HBO 4th generation. Optimal price/quality balance.

2.3. Iridium spark plugs

Top market segment. The central electrode is made of iridium - metal with a melting point 2466°C (higher than platinum). Total electrode thickness 0.4–0.6 mm, which allows you to create more powerful and stable spark.

• ✅ Pros:
  • Resource up to 100–120 thousand km (on some engines up to 150 thousand km).
  • Minimum breakdown voltage - reduces the load on the coils.
  • Better ignition of the mixture - increase in power up to 3–5%.
  • Resistance to erosion and soot.
• ❌ Cons:
  • The most expensive (from 800–2500 rub. per piece).
  • Useless on older carburetor engines.
  • There are a lot of fakes - there is a risk of running into a fake.

🔹 Who is it suitable for: sports cars, turbocharged engines, engines with direct injection (FSI, TSI). Also relevant for hybridswhere efficiency is important.

2.4. Silver and copper candles

Rare and specific option. Silver spark plugs have a central electrode with silver plating, and copper ones - with a copper core. Their features:

• 🥈 Silver:
  • Excellent thermal conductivity - do not overheat.
  • Used in motorcycles and old Japanese cars (for example, Mazda RX-7).
  • Resource 20–30 thousand km.
• 🔧 Copper:
  • Good electrical conductivity - stable spark.
  • Often installed on Soviet cars (VAZ, Moskvich).
  • Now they are practically not produced.

🔹 Who is it suitable for: collectors of retro cars or owners of equipment, where the manufacturer directly indicates the need for such candles.

2.5. Multi-electrode spark plugs

The peculiarity of these candles is: multiple side electrodes (usually 2–4). The idea is that the spark will always find the shortest path to ground, even if one of the electrodes is coated with carbon deposits or worn out.

• ✅ Pros:
  • Longer service life due to uniform wear.
  • Stable operation even with poor fuel.
• ❌ Cons:
  • The spark can “walk” between the electrodes - unstable ignition.
  • Not always justified by price (more expensive than regular nickel ones).

🔹 Who is it suitable for: auto with bad fuel or frequent voltage drops in the on-board network.

3. Heat number: what is it and how to choose

Heat number - this is an indicator thermal characteristics candles, that is, its ability to remove heat from the electrodes. The higher the number, the “cooler” the candle (it removes heat better). A low number means a “hot” plug that gets hotter.

Why is this important? If the spark plug is too hot, it may cause glow ignition — spontaneous ignition of the mixture from a hot electrode (and not from a spark). This leads to detonation, burnout of pistons and valves. A spark plug that is too “cold,” on the contrary, will become covered with soot and stop working.

Heat number	Candle type	For which engines	Examples of cars
8–14	Hot	Low-power naturally aspirated engines, old carburetor cars	VAZ 2101–2107, GAZ 24
16–19	Average	Modern naturally aspirated engines, injection cars	Toyota Corolla, Hyundai Solaris
20–26	Cold	Turbocharged, forced engines, sports cars	Subaru WRX, BMW M5
30+	Ultracold	Racing engines, high compression engines	Nissan GT-R, Porsche 911 Turbo

⚠️ Attention: Heat number not unified between brands! For example, a candle NGK BPR6ES (number 6) roughly corresponds to Bosch WR7DC (number 7), but not Denso W16EXR-U (number 16). Always check with catalog numbers or tables of interchangeability.

How to choose the heat number?

• 📖 Instructions for use - the first source. The manufacturer indicates the recommended number.
• 🔧 If there is no documentation:
  • For atmospheric engines usually fit spark plugs with the number 16–19.
  • For turbo — 20–26.
  • If the engine forced (chip tuning, increased compression) - take 1-2 units “colder”.

What happens if you put the wrong candles according to the heat number?

If the spark plug is too hot:

- Overheating of electrodes → glow ignition (the engine continues to run after the ignition is turned off).

- Detonation → destruction of pistons and valves.

- Melting of electrodes.

If the spark plug is too cold:

- Abundant soot → misfire.

- Poor starting in cold weather.

- Increased fuel consumption (up to 10–15%).

4. Gap between electrodes: how to check and adjust

Gap is the distance between the central and side electrodes. It depends on:

• 🔥 Spark power - the larger the gap, the stronger the discharge, but also the higher the requirements for the coil.
• ⚡ Breakdown voltage — a small gap facilitates the formation of a spark, but reduces its area.
• 🚗 Operation stability — an incorrect gap leads to misfires.

Standard clearance values:

• 🔧 Carburetor engines: 0.7–0.9 mm.
• 🔧 Injection atmospheric: 1.0–1.1 mm.
• 🔧 Turbocharged and direct injection: 0.8–1.0 mm (sometimes less).
• 🔧 For gas (GBO): 0.7–0.8 mm (the gas-air mixture ignites worse than gasoline).

How to check and adjust the gap:

1. Unscrew the spark plug and clean it of carbon deposits (with a brush or sandblast).

2. Take spark plug probe (or a set of flat probes).

3. Insert the probe between the electrodes - it should enter with slight pinching.

4. If the gap is less than normal, carefully bend the side electrode (you can use a flat screwdriver).

5. If the gap is larger, knock out the electrode with light blows (but do not overdo it so as not to break it!).-->

⚠️ Attention: B iridium and platinum adjust spark plug gap it's impossible - this will damage the spraying! If the gap is not normal, the spark plug needs to be replaced.

5. Gas candles (GBO): which ones are better to choose?

If your car is equipped gas equipment (GBO), special requirements are imposed on candles. The point is that the gas-air mixture ignites worse than gasoline - she needs a more powerful and hotter spark. In addition, gas combustion occurs at a higher temperature, which accelerates wear of the electrodes.

What happens to standard gas spark plugs:

• 🔥 Electrodes overheat — risk of glow ignition.
• ⚡ Gap increases due to erosion - misfires.
• 🛢️ Carbon deposits are formed faster (especially with poor gas adjustment).

Which candles to choose for HBO:

• 🔥 Electrode material:
  • 🥇 Iridium or platinum - the best option. Resistant to high temperatures.
  • 🥈 Nickel with reduced clearance (0.7–0.8 mm) is a budget solution.
• 🔥 Heat number:
  • For HBO 2–3 generations (carburetor, injector with emulator) - on 1–2 units colderthan for gasoline.
  • For HBO 4 generations - the same as for gasoline (modern systems themselves adjust the composition of the mixture).
• 🔥 Brands:
  • Denso Iridium Power (series IW20 for gas).
  • NGK LPG LaserLine (special series for HBO).
  • Bosch Platinum WR7DP (universal for gasoline/gas).

🔹 Advice: If, after installing the HBO, the engine begins to “trouble” or has trouble starting, first check the spark plugs. Often the problem is solved by replacing it with "gas" models with less clearance.

6. How to choose spark plugs by car make

The most reliable way to choose candles is to use catalog numbers manufacturer. But what if you don’t have them at hand? Let's figure out how to choose candles according to parameters.

📌 Main selection criteria:

1. Thread size:
   • M14×1.25 — the most common (most foreign cars).
   • M18×1.5 - old domestic cars (VAZ, GAZ).
   • M12×1.25 - some motorcycles and small cars.
2. Thread length:
   • 19 mm — short (many Japanese cars).
   • 25 mm - standard (most European and Korean cars).
   • 26.5 mm - extended (some American engines).

Socket type:

• Flat - requires an o-ring.
• Conical — without a ring (tightness due to the cone).
• Heat number (see table in section 3).
• Gap (see section 4).

🔍 Where to find data for your car:

• 📄 Instructions for use — section “Maintenance”.
• 🖥️ Official websites of candle manufacturers:
  • NGK (catalog by VIN or model).
  • Denso (search by parameters).
  • Bosch (selection by car brand).
• 🔧 Spare parts databases:
  • Autodoc, Exist.ru, Emmegi.

⚠️ Attention: If you are buying candles unoriginal, be sure to check:

• 🔧 Length of threaded part - if the spark plug is too long, it will hit the piston!
• 🔧 Contact type - some candles require individual coils (for example, VW/Audi with the system Coil-on-Plug).
• 🔧 Presence of resistor - if your system has noise suppression resistor, spark plugs without it will damage the electronics.

💡

Never buy candles based only on appearance! Two identical-looking spark plugs may have different thread lengths, heat ratings, and electrode materials. Always check the part number or parameters.

7. Signs of faulty spark plugs

How do you know when it's time to change the spark plugs? Here main symptoms:

• 🚗 Engine troubles — misfires in one or more cylinders.
• 🔥 Bad start - especially in cold weather (the spark plugs are leaking, the spark is weak).
• ⚡ Dips during acceleration — the engine is “stupid” and does not pull.
• 🛢️ Increased fuel consumption (on 10–20%) - the mixture burns ineffectively.
• 💨 Smoke from the exhaust - black (rich mixture) or white (oil in the combustion chamber).
• 🔊 Detonation — metallic knocking noise under load (the spark plugs overheat).

🔍 How to check spark plugs:

1. Unscrew the spark plug and inspect it:
   • 🔥 Normal Wear — light gray or brown coating, electrodes are intact.
   • ⚠️ Thread oil - problem with valve stem seals or piston rings.
   • ⚠️ Black soot - rich mixture (sensor or injector malfunction).
   • ⚠️ White coating - lean mixture or overheating.
   • ⚠️ Melted electrodes - detonation or incorrect heat rating.

Check the clearance (see section 4).

Test the spark:

• Place the spark plug on the high-voltage wire, place the housing against ground and crank the starter.
• There must be a spark bright, blue and stable. A weak orange spark is a sign of a malfunction.

⚠️ Attention: If there are any on the candles cracks on the insulator or melting of electrodes, they need to be replaced urgently! This may lead to breakdown of the ignition coil (repair cost - from 5,000 rub.).

8. Top 5 myths about spark plugs

There are many myths surrounding candles that prevent you from making the right choice. Let's look at the most common ones.

• 🚫 Myth 1: “Iridium spark plugs increase engine power”

  ✅ Reality: The increase in power (if any) is associated not with the material, but with spark purity. On a working engine the difference is 1–3%, which is imperceptible in everyday driving. The main advantage of iridium is resource, not power.

• 🚫 Myth 2: “Plugs need to be changed every 10,000 km”

  ✅ Reality: Service life depends on electrode material:

  • Nickel: 20–30 thousand km.
  • Platinum: 80–100 thousand km.
  • Iridium: 100–120 thousand km.

  Change spark plugs according to the manufacturer's instructions, and not by eye.

• 🚫 Myth 3: “The more electrodes, the better”

  ✅ Reality: Multi-electrode spark plugs last longer, but do not improve inflammation. The spark always follows the path of least resistance, so additional electrodes are a “replacement”