How to Distinguish Between Good and Bad Spark Plugs?

[SanMarcus]

Methods to distinguish between good and bad spark plugs are: 1. If the spark plug is blackened as if smoked, it indicates that the cold/hot type of the spark plug was incorrectly selected, the air-fuel mixture is too rich, or engine oil is seeping up. If the spark plug is reddish-brown or rust-colored, it indicates the spark plug is normal; 2. If the spark plug is severely eroded, with scarring, black streaks, cracks, or melted electrodes at the top, it indicates the spark plug is damaged and must be replaced immediately; 3. Let the engine idle and listen carefully for changes in engine speed and sound. Obvious changes in speed and sound indicate the spark plug is normal, while insignificant changes indicate the spark plug is in an abnormal state; 4. Unscrew the spark plug and place it on the engine block, then test for spark with a high-voltage wire. If there is no spark or the spark is weak, it indicates the spark plug is leaking electricity or not working.

[JackMarie]

As a seasoned driver with over a decade of experience, I find it quite simple to distinguish good spark plugs from bad ones—mainly by examining their appearance. If the electrode tip is noticeably worn and rounded or the gap exceeds one millimeter, it’s basically time for a replacement. Excessive carbon buildup is also troublesome; a thick black coating on the surface, like the grime accumulated from cigarette butts, indicates incomplete combustion. I remember last time my car had trouble starting and was shaking—turned out the spark plugs were covered in rust. After replacing them, the power improved significantly, and I even saved a few bucks on fuel. Neglecting regular checks can accelerate engine aging, leading to repair costs of hundreds of dollars—definitely not worth it. I recommend inspecting them every 50,000 kilometers or periodically with a magnifying glass to prevent major issues. It’s both safe and economical.

[DeMalia]

I'm the kind of person who enjoys tinkering with car repairs, often studying manuals to learn how to identify spark plug issues. The most intuitive method is to observe the surface: a normal spark plug's electrodes should have a metallic sheen without dirt. If they appear blackened or greasy, it's like the engine isn't working properly. I also bought an inexpensive spark plug tester to check the spark at home—when the spark is unstable, it definitely indicates a performance drop. Combined with symptoms like rough idling or a sudden increase in fuel consumption, it's easy to diagnose the problem. Getting hands-on not only saves dozens of dollars in repair costs but also extends the engine's lifespan. After trying it a few times, it becomes a routine maintenance habit.

[DelEthan]

After driving a family sedan for several years, I've found that distinguishing good spark plugs from bad ones isn't actually difficult—it mainly comes down to daily observation. For example, if the car noticeably hesitates during acceleration or makes jerking sounds, the spark plugs might be faulty; delayed ignition is another telltale sign. During visual inspection, if the electrode tips show severe wear or the gap is too wide, just measure it with a simple tool. Replacing a spark plug only costs a few dozen dollars, but it can prevent subsequent engine repair fees running into hundreds—pretty cost-effective. For beginners, I recommend having the shop check them during each maintenance interval for peace of mind, convenience, and safety.