The question of when to change spark plugs — strictly according to the maintenance schedule or based on their actual condition — causes no less debate among car owners than the choice between 92 and 95 octane gasoline. Some drivers follow the manufacturer's recommendations, believing that the manufacturer knows best when this consumable part needs replacement. Others are confident: if the spark plugs look normal and the engine starts without problems even in severe frost, then they can be left alone until a mileage of 60–90 thousand kilometers. Let's try to figure out what neglecting the replacement intervals set by the manufacturer can lead to.
Why the engine needs spark plugs
First, it's worth recalling the role spark plugs play in engine operation. Their task is to create a spark when the ignition is turned on, which ignites the air-fuel mixture in the cylinder's combustion chamber. This process occurs due to an electrical discharge with a voltage of several thousand or tens of thousands of volts, arising between the spark plug electrodes.
The design of a conventional spark plug includes several elements:
- terminal — serves to connect the spark plug to the high-voltage wires of the ignition system or directly to the coil;
- insulator — protects the spark plug from overheating; its part adjacent to the central electrode especially strongly affects the spark plug's operation;
- insulator ribs — prevent electrical breakdown along the surface;
- central and side electrodes — it is between them that the spark is formed, igniting the air-fuel mixture;
- seal — prevents hot gases from the combustion chamber from penetrating.
The key parameter of any spark plug is the gap size between the central and side electrodes. The efficiency of mixture ignition directly depends on it. The larger the gap, the more powerful the spark and the wider the combustion zone. As a result, fuel burns more completely, consumption remains stable, and the engine runs smoothly. However, if the gap is reduced, the spark appears faster, and breakdown occurs at a lower voltage. But such a spark has less energy, which worsens the ignition of the mixture and ultimately leads to a decrease in engine power and efficiency.
Another important characteristic is the heat rating, which indicates the maximum permissible thermal load of the spark plug. Domestic spark plugs are produced with heat ratings of 8, 11, 14, 17, 20, 23, and 26. Foreign manufacturers do not have a unified scale. According to this parameter, spark plugs are divided into "cold," "hot," medium, and universal. Too "cold" spark plugs with a high heat rating self-clean worse, which leads to engine misfires. If the spark plugs are too "hot," pre-ignition is possible, which in symptoms and consequences resembles detonation.
Types of spark plugs
In colloquial speech, spark plugs are usually divided into classic, platinum, and iridium.
These names are associated with the materials from which the electrodes are made. Classic spark plugs have copper electrodes, platinum ones have platinum, and iridium ones have a special iridium alloy. In some classic models, copper electrodes are additionally coated with an yttrium alloy, which increases their resistance. Platinum spark plugs are valued because platinum almost does not burn out, has high corrosion resistance, and withstands high temperatures, which gives a long service life. Iridium spark plugs have similar properties. The longest lifespan is in spark plugs where the electrodes are made of a platinum-iridium alloy.
Spark plug service life
The durability of spark plugs is determined by many factors. Manufacturers calculate the resource of these elements based on the electrode material, as well as approximate operating conditions — climate, fuel quality, and so on. Thus, classic spark plugs on average last no more than 50 thousand kilometers, and platinum and iridium ones — up to 90 thousand. Of course, these indicators can change, for example, depending on the quality of the gasoline used or the condition of the engine itself. Therefore, many automakers advise changing classic spark plugs at every second scheduled maintenance — say, after 30 and then 60 thousand kilometers. If platinum or iridium spark plugs are used, the interval can be increased by one and a half to two times.
Consequences of untimely replacement
Suppose the spark plug replacement interval specified in the maintenance schedule has already passed, and the car owner has not installed new ones. Perhaps nothing terrible will happen to the engine immediately. But at some point, the car simply will not start. Therefore, it is worth paying close attention to the signs that indicate the imminent failure of the spark plugs.
Such signs include:
- engine "misfiring" (jerking while driving and at idle);
- difficult starting (the starter cranks, but ignition does not occur);
- increased fuel consumption;
- increased CO emissions;
- deterioration of dynamics (the engine does not reach maximum RPM, power drops).
If these symptoms are ignored, the engine may fail.
One of the most serious consequences of spark plug problems is detonation in the combustion chamber. During detonation, a shock wave arises in parts of the mixture, which, depending on the volume of the mixture, can be so powerful that it provokes detonation of the entire remaining charge in the cylinder. When shock waves reflect from the walls of the combustion chamber, a metallic ringing is heard. With severe detonation, knocks become louder, power drops, and black smoke comes from the exhaust pipe. In addition, the engine experiences serious thermal and mechanical loads. The edges of pistons, cylinder head gaskets, and spark plug electrodes can burn out. Shock waves destroy the oil film in the upper part of the cylinder, accelerating its wear.
Conclusion:
- - The engine should be equipped with spark plugs recommended by the manufacturer, taking into account the heat rating and other characteristics.
- - Even if the ignition system operates stably, spark plugs should be checked at every scheduled maintenance.
- - Long-term operation (mileage from 50 thousand kilometers) is justified when using spark plugs with platinum or iridium electrodes.
- - To extend the life of spark plugs, it is worth refueling only with proven fuel, timely replacing filters, and monitoring the correct spark plug gap.
- - At the first signs of malfunction — "misfiring," increased fuel consumption, unstable RPM — you should urgently contact a service station or replace the spark plugs yourself.
