Spark plugs are the engine component responsible for igniting the air-fuel mixture in each cylinder. Despite their small size, they work under extreme conditions of heat, pressure, and electrical stress. Understanding spark plugs helps UK drivers maintain optimal engine performance and identify problems early. ## Types of Spark Plugs **Copper spark plugs** have a solid copper core centre electrode with a nickel alloy tip. They offer excellent conductivity and are the original design, but the soft copper material wears relatively quickly. Copper plugs are typically specified for older vehicles and are the least expensive option, priced at £2-5 per plug. **Platinum spark plugs** use a small platinum disc centre electrode that lasts approximately twice as long as copper. Platinum is harder and more resistant to erosion, making these plugs suitable for modern engines with higher combustion temperatures. Prices typically range from £5-15 per plug. **Iridium spark plugs** feature an extremely fine iridium centre electrode, typically just 0.6mm in diameter. Iridium is one of the hardest metals, offering excellent wear resistance and providing a stronger spark with less voltage required. Most modern engines are factory-equipped with iridium plugs, lasting 60,000 to 100,000 miles. Prices range from £8-25 per plug. **Double platinum spark plugs** have platinum electrodes on both the centre and ground electrode. These are commonly used in wasted-spark ignition systems where two plugs fire simultaneously. They offer extended life and are often recommended for hybrid vehicles that frequently switch between petrol and electric power. ## Replacement Intervals Standard copper spark plugs should be replaced every 20,000 to 30,000 miles. Platinum plugs last 40,000 to 60,000 miles, while iridium plugs can operate effectively for 60,000 to 100,000 miles. Always check your vehicle's specific recommendation in the owner's handbook. These intervals assume normal driving conditions. Short journeys where the engine rarely reaches full operating temperature can reduce plug life because combustion by-products do not burn off the electrodes properly. Extended idling also deposits more contaminants on the plugs. Vehicles with high mileage that have never had spark plugs replaced often suffer from worn electrodes that cause misfiring, poor starting, and rough running. At this point, the engine may run acceptably but will have reduced power and increased fuel consumption. ## Signs of Worn Spark Plugs Engine misfire is the primary symptom of failing spark plugs. You may feel a shudder through the accelerator, hear an irregular popping from the exhaust, or notice the engine light flashing. Misfiring damages the catalytic converter and should be addressed promptly. Difficult starting, particularly when the engine is cold, can indicate worn or fouled spark plugs. The spark required for cold starting is more demanding, and worn electrodes may not provide sufficient spark energy for reliable ignition. Increased fuel consumption often accompanies worn spark plugs. Inefficient combustion means more fuel is wasted with each cycle, leading to noticeably worse economy. A 5-10% increase in fuel consumption is common with degraded spark plugs. Rough idle and poor acceleration result from inconsistent combustion. The engine may shake at idle or hesitate during acceleration. These symptoms often develop gradually and may be attributed to other causes, making spark plug inspection worthwhile during any driveability investigation. ## Frequently Asked Questions **Can I replace spark plugs myself?** Spark plug replacement is a straightforward maintenance task on most vehicles. The main challenge is accessing the plugs in modern engines with deeply recessed cylinder head designs. Budget £30-100 for labour if you are not confident doing it yourself. **Do I need to gap my spark plugs?** Pre-gapped iridium and platinum plugs are supplied ready to install. Copper spark plugs often need gapping using a feeler gauge. Always check the specified gap against the manufacturer's data before fitting any spark plug. **What do worn spark plugs look like?** Worn spark plugs show rounded centre electrodes, eroded gap widening, and white or black deposits on the insulator. Oil-fouled plugs indicate engine problems requiring investigation. Brownish deposits are normal and indicate proper combustion.

Official Resources: GOV.UK Check Vehicle Tax | GOV.UK Vehicle Tax | DVLA Online | MOT Check

Frequently Asked Questions

Q: How much is car tax (VED) in the UK 2026?
Car tax rates in the UK depend on your vehicle's CO2 emissions and list price. Standard rates start from £190 per year for petrol and diesel cars, with zero-rated VED for EVs. First-year rates vary from £0 to £2,605 depending on emissions. Additional premiums apply for vehicles over £40,000.

Q: How do I check if my car is taxed online?
You can check your vehicle's tax status for free on the Gov.uk website at gov.uk/check-vehicle-tax. You'll need your vehicle's registration number (number plate). You can also check via the Motor Insurance Database to verify road tax and insurance status simultaneously.

Q: Can I get a refund on car tax if I sell my vehicle?
Yes — if you sell or scrap your vehicle, you can claim a refund on any full months of remaining road tax. Contact DVLA with the V11 reminder letter or apply online at gov.uk. Refunds are usually processed within 4-6 weeks.

Q: Is road tax refund available when transferring ownership?
No — road tax does not transfer with the vehicle. When you sell your car, the tax is automatically cancelled and any remaining months are refunded to you by DVLA. The new owner must tax the vehicle immediately. As a buyer, always verify the vehicle's tax status before purchasing. Related: Car Tax vs Motorcycle Tax UK 2026 | Car Tax and Vehicle Modifications UK 2026 | UK Car Air Filter Guide 2026 | UK Car Camshaft Phaser Guide 2026.

Q: What is the luxury car tax threshold in the UK 2026?
The additional rate for vehicles over £40,000 (list price) adds £410 per year to standard VED rates for years 2-6 of registration. This surcharge brings the annual cost for high-emission vehicles over £40,000 to around £600-690 per year. Pure EVs under £40,000 pay zero VED.