When a specialized candle key isn’t handy, many car owners reach for whatever is nearby. Experts at Za Rulem, Russia’s oldest and most trusted automotive publication, explain the risks of this shortcut and how it can compromise engine health.
The first mistake is using an improvised tool to loosen or remove the spark plug. If a tall cap is used instead of a proper spark plug wrench, the plug can slip and drop to the bottom of the hollow cavity. The impact tends to bend the side electrode, narrowing the gap and disrupting the spark. That small change can hurt engine performance and shorten its life.
Most engines require a 16 millimeter spark plug wrench, though some models deviate. For Citroën and Peugeot vehicles, a 14 millimeter wrench is the correct size. Using the wrong size wrench risks rounding the plug’s nut, making removal even more difficult and potentially damaging the thread in the cylinder head.
The second mistake involves the tightening torque. The service manual or the packaging on the plugs specifies the correct torque. A torque wrench is the reliable way to verify this, yet not everyone owns one. Underdone torque allows gases to leak past the seals, causing the plug to foul with soot and the engine to run irregularly. Over-tightening can crack the ceramic insulator, fragmenting pieces that may enter the combustion chamber and harm piston rings or valves.
Third, some drivers try to alter the electrode gap to improve performance. For modern engines, changing the gap is not advised and can degrade combustion quality, reducing power and efficiency. In addition to diminished performance, improper gaps can shorten the engine’s lifespan by stressing ignition and fuel delivery systems.
For a comprehensive look at how to replace plugs correctly and avoid common mistakes, see the original guidance by Alexei Revin and Mikhail Kolodochkin on candles replacement and engine risk. Readers are encouraged to consult the authoritative tips and follow vehicle-specific recommendations from the manufacturer, as well as professional diagnostics when in doubt.