Problems with poor starting, rough running, or high fuel consumption? – It could be the spark plugs!

Put in its simplest form, the purpose of a spark plug is to provide the spark – a high voltage electrical charge that ‘jumps’ the gap between its electrodes – that ignites the fuel and air mixture that enters the combustion chamber in the cylinder head, to power the engine. It is, therefore, a vital part of your car, so only high quality spark plugs should be used. 

However, in common with almost every part of your car, spark plugs only have a certain lifespan because during their normal use, they gradually wear, so will need to be replaced at some point. In addition, for engine performance reasons, they may need to be upgraded to a more suitable type.

The primary reason that spark plugs need replacement is due to erosion to the electrode, which is caused by the aggressive nature of the spark itself. Each time the spark jumps the gap, it erodes an almost immeasurably small amount of material from the electrodes. However, over its lifespan, this will happen millions of times, which gradually increases the gap and reduces the efficiency of the spark, affecting engine performance and increasing exhaust emissions and fuel consumption. In addition, if the gap becomes too wide, as well as a drop in engine efficiency, extra strain is put on the ignition coil for example, as it needs to generate a higher voltage for the spark to jump the larger gap. 

The amount of wear that the electrodes suffer is primarily governed by the material that they are made of. With the development of nickel electrodes, which incidentally, is now considered to be the basic automotive spark plug technology, the previous requirement to periodically reset the gap was superseded, primarily as the material is more hardwearing. 

However, erosion still occurs, to the extent that after around 30,000miles/50,000km, the electrodes will be very worn, so the plugs will have reached the end of their service life.

It is worth mentioning that although spark plug wear is completely normal, there are factors, such as modern driving habits, new fuel types and variable weather conditions, that can accelerate the rate of wear and will mean that the plugs will have to be changed more frequently. Worn electrodes can cause rough engine running, misfires and starting issues, although there are also other factors related to spark plugs that cause starting issues. Under certain conditions, moisture can build up in the combustion chamber, which then gathers on the electrode, and makes it more difficult for the spark to jump the gap. This problem is made worse with the recent change in the specification of petrol from E5 to E10, which is prone to attracting higher levels of moisture. However, modern, post pandemic driving habits, which have seen vehicles used less frequently and for shorter journeys, also have a similar effect, as the engine often doesn’t reach its optimal operating temperature before it’s parked, and fuel in the tank takes longer to be used, so over time, more water accumulates in the tank. All of these issues primarily reveal themselves in engine starting difficulties and fitting new spark plugs may be the correct solution.

In addition to replacing the plugs more frequently, there is another way to actually make the ignition more resistant to these factors, namely to upgrade the spark plugs with those of a different technology and electrodes made from more durable materials, such as platinum or iridium. 

Upgraded spark plugs can increase power, while reducing exhaust emissions and improving fuel consumption, as well as requiring less energy from the ignition coil. Another benefit is that the use of these hardwearing materials mean that they also have a much longer service life, sometimes up to 75,000miles/120,000km, at which point however, they will need to be replaced. 

Although changing spark plugs is a relatively straightforward process, not everyone is confident enough to tackle the job themselves. However, your local independent workshop will be able to help advise you of the most appropriate replacement, whether a like for like original, or an upgraded version, and undertake the job so that your car performs at its best.