Some say spark plugs need to be replaced every 20,000 kilometers, while others claim they can last up to 100,000 kilometers without any issues.
So, whose advice should you follow? How can you determine whether your spark plugs need to be replaced?
This article will break it down for you.
Different spark plug materials have different lifespans
First, spark plugs come in various types and materials, and their lifespans vary depending on the material.
For example, the cheapest nickel-alloy spark plugs cost around 20 yuan each and have a relatively short lifespan, typically needing replacement after 20,000 to 30,000 kilometers.
Higher-quality options, such as platinum, iridium, or iridium-platinum spark plugs, can last longer.
The most expensive ruthenium spark plugs can even last up to 150,000 kilometers.
Different engine technologies also affect spark plug lifespan
Does that mean upgrading to a better spark plug will allow you to go 100,000 or 150,000 kilometers without replacement?
Not necessarily.
Different engine technologies also impact spark plug lifespan.
For instance, turbocharged engines tend to have shorter spark plug lifespans.
Compared to naturally aspirated engines of the same displacement, turbocharged engines place higher thermal and mechanical loads on the cylinders.
This means turbocharged engines demand more from spark plugs in terms of resistance to thermal shock, electrical erosion, mechanical impact, corrosion, and sealing, leading to faster wear and tear.
It’s like comparing someone who smokes, drinks, and stays up late partying every day to someone who maintains a regular sleep schedule—the former is likely to be in worse physical condition than the latter.
Some automakers also incorporate more advanced technologies into their engines. For example, BMW’s B-series engines recommend replacing spark plugs every 20,000 kilometers.
This is because these engines use continuous ignition technology. While a typical engine ignites once per fuel injection, BMW’s system ignites 3 to 8 times.
With more frequent ignitions, the spark plugs naturally wear out faster.
So, when some automakers require shorter spark plug replacement intervals, it’s not necessarily a scheme to squeeze more money out of owners.
Engine operating conditions also affect spark plug lifespan
Another easily overlooked factor is the operating conditions.
Highway driving and stop-and-go city traffic create different engine conditions, which in turn affect the state of the spark plugs.
During traffic jams, the engine typically runs at lower RPMs.
This leads to incomplete combustion of the fuel in the combustion chamber. Some of the unburned fuel mixture is expelled, while the rest adheres to the combustion chamber and spark plugs, forming what is commonly known as carbon deposits.
In some cases, engines may also burn oil, which can further contribute to carbon buildup on the spark plugs, hindering their proper function.
Therefore, whether and when spark plugs need to be replaced depends on the specific vehicle model and driving conditions, meaning there is no one-size-fits-all replacement standard.
How to Determine Whether Spark Plugs Need Replacement
After all that, how can you actually tell if your spark plugs need to be replaced?
Well, we can actually take them out and inspect them.
First, check the gap of the spark plug—that small space between the center electrode and the ground electrode.
As the spark plug operates, the electrodes gradually wear down, causing the gap to widen. This reduces the discharge performance, weakening the spark and affecting engine operation.
Usually, the maintenance manual will specify the normal range for the spark plug gap. If it exceeds this range, it needs to be replaced. If this information isn’t available, you can always ask customer support.
Aside from the gap, we can also assess the condition of the spark plug to determine whether it needs replacement.
As mentioned earlier, if there’s too much carbon buildup, the spark plug may leak electricity, produce weak sparks, or even fail to spark at all. In such cases, it’s time for a replacement.
Additionally, if the spark plug operates at excessively high temperatures or has low strength, it may experience erosion.
In simple terms, the electrodes can melt due to high heat, rendering the spark plug unable to function properly.
Here’s something interesting: spark plugs can also "poison."
Sounds alarming, right? This actually happens when gasoline containing MMT (methylcyclopentadienyl manganese tricarbonyl) as an anti-knock agent is used.
The byproduct of MMT combustion is primarily manganese tetroxide, which accumulates on the spark plug. When you remove the spark plug, you might notice reddish deposits—this indicates manganese poisoning, and the spark plug must be replaced.
However, nowadays, standard finished gasoline does not contain MMT.
As long as you avoid sketchy, unregulated gas stations and refrain from using low-quality fuel additives, your spark plugs generally won’t experience poisoning.
So, the recommendation to replace spark plugs every certain number of thousands of kilometers is really just a guideline.
Whether they actually need to be replaced depends on the size of the gap and whether there are signs of carbon buildup or erosion.
