The service schedule for many vehicles these days won’t include a fresh set of plugs until 100,000km or more.

What hasn’t changed is that it’s still vital that replacement sparkplugs meeting the vehicle manufacturer’s original specifications are installed to avoid severe engine damage, ensure proper vehicle performance and maximum plug life.

Plugs have to ‘fit’ correctly, so that means correct ‘reach’ (the length of the threaded nose), correct seat design (the sealing taper or gasket), correct nose thread and diameter, plus the right electrode design, projection and material type.

Sparkplugs are designed to run at a temperature that ensures they don’t foul with combustion deposits, but cool enough to avoid ‘pre-ignition’, plug or engine damage.

Therefore, it’s vitally important the specified heat range plug is used in a standard (unmodified) engine.

Modified engines, including those converted to LPG, may require a different heat range plug and professional advice should be sought.

Sparkplugs incorporating precious metals, such as platinum and iridium, are frequently specified and can be substantially dearer.

Don’t substitute cheaper ‘standard’ plugs though, as they have different firing qualities.

The gap between the electrodes needs to be checked and set to the correct specification for the engine.

Precious metal plugs usually come with the gap pre-set to the correct gap for the specific engine, as the laser-welded electrode tips can be easily damaged.

Some vehicle makers specify a resistor plug with an internal resistor to prevent interference with sensitive electronics including on-board engine management systems.