Spark plugs are one of the most crucial components ensuring the engine's operation. The condition of the spark plugs affects the quality of the combustion of the fuel-air mixture, and thus the overall efficiency of the internal combustion engine. We explain how automotive spark plugs differ from each other and how to make the right choice when selecting them.
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How a spark plug works
What are spark plugs for in a car? They ignite the mixture of gasoline and air in the cylinders. A high voltage of 25–30 thousand volts is applied to the closely positioned elements of the spark plug (electrodes). This creates a spark that ignites the fuel-air mixture in the cylinders when starting and running the engine. The principle of operation of spark plugs in a gasoline engine is not complex, but there are many nuances in the construction of this component that affect its parameters. Perhaps the most important of these is the heat rating.
What is a heat rating?
During operation, automotive spark plugs heat up significantly because they are in direct contact with the combustion chamber. However, high temperatures on the surfaces of the electrodes cause unauthorized and premature ignition of the fuel mixture. As a result, the engine begins to vibrate, fuel consumption increases, and power decreases. This adverse process is called pre-ignition. Spark plugs have a characteristic known as heat rating. This value is determined by the time it takes for the spark plug to reach a state that leads to pre-ignition in laboratory experiments. In simpler terms, the heat rating shows the spark plug's ability to dissipate excess heat.
And this is one of the main parameters by which spark plugs differ. There is no single standard for designating the heat rating. Each spark plug manufacturer encodes it in their marking in their own way. But it is easy to find comparison tables of heat ratings in the markings of different brands of spark plugs online.
However, one should not assume that a low heat rating is always good and a high one is bad. After all, it is at high temperatures (not below 400 degrees) that the deposits on the electrode surfaces burn off. This is their self-cleaning, allowing the spark plug to function properly for a long time. Therefore, "colder" spark plugs are more prone to contamination during operation.
How spark plugs are constructed
A spark plug consists of four main elements: a metal shell, a ceramic insulator, and central and ground electrodes. There are two distinct types of spark plugs: single-electrode and multi-electrode. The most common single-electrode design has a central and one ground electrode, between which the spark forms. Spark plugs of this design are the most affordable, but have a limited lifespan and may not allow the engine to reach its full potential, especially if it is a turbocharged engine with high power potential and combustion chamber pressures.
A multi-electrode spark plug features two to four ground electrodes. Due to the direction of the spark, this design ensures a more even flame front (burning direction across the engine cylinder), which positively affects the smoothness of engine operation. This is especially noticeable at idle. Another advantage of the multi-electrode design is that the spark "chooses" the most suitable (e.g., the least contaminated at the moment) ground electrode for its formation. This means it always has the maximum possible power. Thus, the technological features of multi-electrode spark plugs can improve engine performance as well as its environmental parameters. The downside is that the cost of these spark plugs is higher than that of single-electrode ones.
Which spark plugs are better?
What factors determine a spark plug's performance? There are several, and one important factor is the material of the electrodes. Spark plugs with copper and nickel electrodes are the most budget-friendly. They allow you to save money, which can be especially noticeable if the engine has six or more cylinders. On the other hand, the lifespan of such spark plugs is relatively short: typically around 30,000 kilometers. So, there may not be much real savings.
Many modern engines require spark plugs with platinum or iridium electrodes. These materials can handle thermal loads much better, allowing for the use of thinner electrodes in spark plugs than in designs with copper and nickel elements, resulting in better spark generation.
These types of spark plugs are not cheap: their cost is 2–3 times higher than those with copper electrodes. However, the price difference can be justified by better fuel economy (up to 3–7 percent). Most importantly, the lifespan of such spark plugs is higher: platinum ones last around 80–90 thousand kilometers, while iridium ones last up to 100 thousand kilometers.
How to choose spark plugs correctly
It is important to purchase spark plugs from the list specified in the car's manual to avoid disrupting the engine's performance. This will also help you avoid mistakes with other spark plug characteristics. These include thread type (typically, automotive spark plugs have M14×1.25 threads) and length—short (12 mm), medium (19 mm), or long (25 mm)—as well as the size of the hex key socket. Currently, 16 and 21 mm are the most common.
As for design and materials, it is better to choose iridium or platinum spark plugs if your budget allows. This is especially important when you have a powerful turbocharged engine. You might also consider multi-electrode copper or nickel spark plugs.
For everyday use in your car, you can use spark plugs with a
medium heat rating from the range specified by the car manufacturer in the
manual. If you prefer dynamic driving, you can install spark plugs with the
highest allowable heat rating. They may also be preferable in hot climates.
When to replace spark plugs
You should replace the spark plugs in your car according to the scheduled maintenance plan, which is typically outlined in the owner's manual. Generally, the replacement interval for spark plugs aligns with their average lifespan—no more than 30–50 thousand kilometers for copper or nickel spark plugs and 80–100 thousand kilometers for platinum or iridium spark plugs. It's best not to wait until the spark plug completely fails, as operating the engine under such conditions can be harmful, particularly for modern engines and catalytic converters.
It is also recommended to check the condition of the spark
plugs during each scheduled maintenance (even if replacement is not planned) or
earlier if the engine's behavior signals poor condition:
·
Reduced power;
·
Increased fuel consumption;
·
Starting problems;
·
Misfires (the engine
"misfires").
Remember that poor-quality fuel with a high content of
harmful additives, especially those containing metals, often negatively affects
the lifespan of spark plugs. This leads to the formation of hard-to-remove
reddish deposits on the electrodes and insulator, which have electrical
conductivity. As a result, the buildup effectively shorts the spark plug's
electrodes, causing it to stop working.
So, in short:
- The main elements of a car's spark plug are the shell, insulator, and central and ground (one or more) electrodes, between which a spark forms.
- One of the main parameters of spark plugs is the heat rating. Spark plugs can be "hot" or "cold," and the optimal heat rating is determined by the engine's design and thermal conditions.
- Therefore, you should choose spark plugs from the list recommended for your car.
- The design of spark plugs can be single-electrode or multi-electrode; the latter are considered more powerful and durable.
- Electrodes can be made from more affordable copper and nickel or from expensive platinum or iridium. The latter last longer.
- Spark plug replacement should be done according to the scheduled maintenance plan and, if necessary, more frequently.{alertSuccess}