Spark plugs are small but mighty — they are responsible for igniting the air-fuel mixture inside your engine’s cylinders. Without properly functioning spark plugs, your engine misfires, loses power, wastes fuel, and produces excess emissions. Yet spark plug replacement is one of the most overlooked maintenance items in vehicle ownership. This 2026 guide covers everything you need to know about when to replace spark plugs for every major vehicle brand — plus what happens when you leave them too long.

What Do Spark Plugs Do?

Each spark plug generates a precisely timed electrical spark inside its cylinder, igniting the compressed air-fuel mixture to create the combustion event that powers the engine. A typical 4-cylinder engine has 4 spark plugs. A V6 has 6. A V8 has 8. In some high-performance engines, each cylinder has 2 spark plugs (twin-spark engines).

As spark plugs age, the electrode gap widens, the tip erodes, and the electrical resistance increases. This means the spark becomes weaker, timing becomes imprecise, and combustion becomes incomplete — wasting fuel and reducing power.

Types of Spark Plugs and Their Lifespans

Brand-by-Brand Spark Plug Replacement Guide

Honda — How Often Should Honda Spark Plugs Be Replaced?

Honda vehicles — including the popular Honda Civic and Honda Accord — are typically factory-fitted with iridium spark plugs. Honda recommends spark plug inspection every 30,000 km and replacement every 100,000 km for iridium-equipped models. For older Honda models with copper plugs, replacement every 30,000–40,000 km is recommended.

Honda Civic (2016–2026): Iridium plugs — Replace every 100,000 km

Honda Accord (2018–2026): Iridium plugs — Replace every 100,000 km

Older Honda models (pre-2012): Copper/platinum — Replace every 30,000–60,000 km

BMW — How Often Should BMW Spark Plugs Be Replaced?

BMW typically uses platinum or iridium spark plugs and recommends replacement every 60,000 km as part of their major service schedule. BMW engines are performance-oriented, and worn spark plugs cause noticeable drops in performance, fuel economy, and smooth idling. Always use BMW-specified spark plugs — incorrect plugs can cause engine damage in high-performance BMW engines.

Hyundai — How Often Should Hyundai Spark Plugs Be Replaced?

Hyundai Elantra and most Hyundai models use iridium spark plugs and recommend replacement every 60,000–100,000 km. Hyundai also recommends visual inspection at every 30,000 km service. Using genuine or OEM-equivalent Hyundai spark plugs ensures correct heat range and gap specification.

Chevrolet — How Often Should Chevrolet Spark Plugs Be Replaced?

Chevrolet recommends spark plug replacement every 60,000–100,000 km for iridium-equipped models. V8-powered Chevrolet vehicles (Silverado, Camaro) require 8 spark plugs per engine — a significant labour and parts cost if deferred too long. The most common Chevy repair for engine performance issues is spark plug and ignition coil replacement.

Signs That Your Spark Plugs Need Replacing

Rough idling: The engine shakes, vibrates, or sounds uneven at idle.

Hard starting: The engine turns over many times before catching, or struggles to start from cold.

Poor fuel economy: Worn spark plugs cause incomplete combustion, burning more fuel.

Engine misfires: A cylinder that fails to fire creates a noticeable jerk or stumble.

Loss of acceleration: The engine feels sluggish or lacks power when accelerating.

Strong fuel smell from exhaust: Unburnt fuel passes through the engine due to misfires.

Check engine light: A misfire fault code often triggers the check engine light.

How Much Does Spark Plug Replacement Cost?

Spark plug cost: $3 to $50 per plug depending on type. Labour: 30 minutes to 2 hours depending on engine accessibility. BMW, Mercedes, and Lexus engines with difficult access can cost $200–$500 in labour alone for a full set. Buying quality spark plugs from APREX AUTO and having a trusted mechanic install them gives the best value.

Frequently Asked Questions (FAQ)

Q: How do I know if my spark plugs are bad?

Symptoms include rough idle, hard starting, poor fuel economy, engine misfires, and check engine light. A mechanic can confirm with a visual inspection.

Q: Can I replace spark plugs myself?

On many vehicles, yes — especially inline 4-cylinder engines with accessible plugs. BMW, Mercedes, and V8 engines are best left to a mechanic.

Q: Do diesel engines have spark plugs?

No. Diesel engines use glow plugs, not spark plugs. Glow plugs heat the combustion chamber for cold starts.