Why Does Fuel Consumption Increase After Replacing Spark Plugs?
2 Answers
The reasons for increased fuel consumption after replacing spark plugs are as follows: 1. The spark plugs are not tightened properly, causing high-pressure gas to leak and reducing cylinder pressure. This makes the engine less efficient, leading to unstable idling or frequent stalling, which naturally increases fuel consumption. In severe cases, it may even damage the engine. 2. Overfilling the engine oil can submerge the crankshaft, increasing resistance. To compensate for the reduced power, the engine consumes more fuel. 3. The spark plugs are of poor quality or the wrong type. How to determine if spark plugs are damaged: Remove the spark plugs and inspect them. Observe their appearance and color to assess their condition. Normal spark plugs have an insulator skirt and electrodes that appear gray-white, gray-yellow, or light brown. A properly functioning spark plug has a reddish-brown insulator skirt, an electrode gap between 0.8-0.9mm, and no signs of electrode burn. If the spark plugs are covered in oil or deposits but are otherwise undamaged, they can be cleaned and reused. If the spark plugs are severely damaged—showing signs of blistering, black streaks, cracks, or melted electrodes—identify the cause of the damage, fix the issue, and replace the spark plugs. Additionally, if the spark plugs appear blackened as if smoked, it indicates the wrong heat range was selected or the air-fuel mixture is too rich, possibly due to oil leakage.
I previously changed the spark plugs and was quite frustrated by the increased fuel consumption. The main issue might lie in the installation details—if the spark plug gap wasn't adjusted properly or if they were overtightened, it could lead to unstable ignition. Incomplete combustion in the engine then raises fuel consumption. Additionally, using mismatched spark plug types, such as ones with incorrect heat ratings, can cause slow engine starts, resulting in insufficient power to meet driving demands. Over time, fuel consumption increases. I recommend rechecking the installation to ensure the spark plugs fit snugly against the ignition coils, or try switching to the manufacturer-recommended model. Also, pay attention to driving habits—avoid aggressive throttle input during the break-in period for new spark plugs. Driving smoothly for a few hundred kilometers might normalize performance. In short, don’t rush to spend money at the repair shop—try troubleshooting yourself first.
