How to Check if a Car Spark Plug is Good?
4 Answers
How to check if a car spark plug is good: Remove the spark plug and observe its condition based on the following appearance colors. A normal spark plug will have its insulator skirt and electrodes in gray-white, gray-yellow, or light brown. A properly functioning spark plug has a reddish-brown insulator skirt, with an electrode gap between 0.8-0.9mm and no signs of electrode burn. If the spark plug is covered in oil or deposits but is not damaged, it can continue to be used after cleaning off the oil and deposits. If the spark plug is severely damaged, showing signs like blistering at the top, black streaks, cracks, or melted electrodes, the cause of the damage should be identified. After troubleshooting, replace the spark plug with a new one. Additionally, if the spark plug appears black as if smoked, it indicates the wrong heat range was selected or the air-fuel mixture is too rich, with oil creeping up. What are the effects of a bad spark plug: A damaged spark plug can directly cause issues such as leakage in the vehicle's ignition system, increased fuel consumption, reduced power, and most notably, difficulty in ignition, affecting the vehicle's normal operation. Severe spark plug erosion, blistering at the top, damage, or melted and eroded electrodes all indicate that the spark plug is ruined and should be replaced.
Checking if a car's spark plugs are working properly is quite simple. Here are a few methods based on my experience. Before starting the car, listen to the engine sound—if there’s irregular shaking or unstable idling, the spark plugs might be faulty. After parking, turn off the engine and wait a few minutes for it to cool down before working to avoid burns or electrical hazards. Use a specialized wrench to remove the spark plugs and inspect each electrode one by one: check for oil stains, carbon buildup, or electrode wear. A normal color is grayish-brown; if it’s too black or shows signs of burning, it’s time for a replacement. You can use a spark plug tester attached to the high-voltage wire to check the spark—only a strong blue spark indicates a healthy plug, while a weak or absent spark means it’s faulty. Pay attention to fuel consumption; if it suddenly increases, it may be due to poor ignition caused by failing spark plugs. It’s recommended to check them every three years or so to avoid breakdowns that could delay your trip. Basic tools can be bought at auto repair shops, and doing it yourself saves time.
After years of driving, I believe the quality of spark plugs directly affects driving smoothness. If the car jerks forward when starting or lacks power when climbing hills, you should suspect spark plug issues. After stopping the engine, carefully remove the spark plug, wipe it clean with a cloth, and check if the electrode gap is too wide or deformed. The normal range should be 0.8-1.0mm, which can be measured with a feeler gauge. Color is also crucial: grayish-brown is good, while blackened ones need cleaning or replacement. Another method is to feel the engine vibration when starting the car—excessive vibration may indicate a faulty spark plug in one cylinder. If you're not comfortable doing it yourself, a professional shop can test it with a tester in seconds. Don't delay these small checks—they ensure long engine life and save fuel costs.
Checking the condition of spark plugs is not complicated. Start the engine and observe if there is any irregular shaking or bouncing. If it runs smoothly, there's no issue; if not, the spark plugs need to be inspected. Turn off the engine and let it cool for a while, then remove one to check its condition: intact electrodes without damage and uniform color are good signs. Use a multimeter to measure the resistance; the normal value should be in the range of several thousand ohms. A significant deviation indicates damage. In terms of symptoms, timely inspection when experiencing acceleration hesitation or difficulty starting can prevent more serious faults. For regular maintenance, avoid letting dirt accumulate, and replace them every few tens of thousands of kilometers to ensure safety.
