Spark plug upgrades

You can spend hundreds of pounds on aftermarket bolt-on products that claim to improve your fuel consumption – some work, others are simply gimmicks. Even so, fitting quality replacement parts can have a greater relevance. 

The spark plug has a very hard life. It must contain forces that equate to fifty times that of gravity, tolerate in excess of 30,000 volts and withstand huge temperature variations. 

Most spark plug electrodes are made from nickel-alloy. Yet, high performance engines employ plugs that use precious metals in their electrodes, such as platinum and iridium alloys. An increasing number of newer high-efficiency engines use these types of spark plugs (pictured) as standard equipment, because they provide a more focussed and precise spark that demands a lower voltage. This results in improved economy/engine performance, better running and improved emissions. Yet, should these spark plug types be specified as standard equipment, never be tempted to downgrade to a cheaper and inferior replacement. 

The experiment 

To find out if these precious metal spark plugs can benefit an average car, I fitted them to a 10 year-old Peugeot, to which the standard-type nickel-alloy plugs previously fitted were still serviceable. Immediately, post start-up, the engine ran smoother with a steadier and smoother idle. After 2,000 miles of motoring, its recorded MPG has increased from 32mpg to 35mpg. 

Therefore, the results of my fairly blunt test leads me to recommend precious metal spark plugs as a useful upgrade for cars that did not have them fitted originally. However, be careful from where you buy them. It has been reported that some online sellers offer premium-priced precious metal plugs but closer scrutiny reveals them to contain no precious metals at all. Sub-standard spark plugs are also rife, as proved by the arrest and subsequent charging of an online trader at the end of May, who sold counterfeit spark plugs that could have caused engine damage. Therefore, our buying advice remains the same for spark plugs as with all car spares – buy recognised brands through recognised suppliers. 

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