What are the effects of not replacing spark plugs on a car?

[PeterLynn]

Not replacing spark plugs can affect the car's fuel consumption, the three-way catalytic converter, and the car's starting performance. Long-term failure to replace them can easily lead to spark plug damage. Spark plug replacement cycle: Under normal maintenance conditions, spark plugs should be replaced after driving 40,000 to 60,000 kilometers. However, this may vary depending on the brand and engine, so it is recommended to follow the user manual. You can refer to the following standards for maintenance replacement: platinum spark plugs should be replaced at 40,000 kilometers, ordinary nickel alloy spark plugs at 20,000 kilometers, and iridium spark plugs at 60,000 to 80,000 kilometers. What are the effects of damaged spark plugs: If the spark plugs are damaged, it can directly cause issues such as leakage in the vehicle's ignition system, increased fuel consumption, and reduced power. The most significant problem is difficulty in ignition, which affects the normal use of the vehicle. Severe spark plug erosion, such as scarring at the top, damage, or melted and eroded electrodes, indicates that the spark plugs are damaged and should be replaced.

[WalterLynn]

I've been driving for over a decade. One time I clearly felt the car had weak acceleration and soaring fuel consumption. Later inspection revealed the spark plugs were overdue for replacement. Not replacing them promptly can lead to insufficient ignition energy and incomplete combustion. Over time, carbon buildup in the engine will become increasingly severe. The scariest part is it can also damage the oxygen sensor, and unburned gasoline in the exhaust may even burn out the catalytic converter. After I replaced the spark plugs that time, the throttle response became crisper and fuel consumption returned to normal levels. I recommend checking ordinary copper-core spark plugs every 30,000 km, while platinum or iridium ones can go up to 60,000 km.

[LoganRose]

Spark plugs may seem like small components, but they directly impact the entire engine. Failure to replace them in time can lead to excessive ignition gaps or electrode corrosion, resulting in unstable combustion. This causes engine shaking, increased noise, and particularly difficult cold starts. Even worse, unburned gasoline can flow through the exhaust pipe and damage the catalytic converter—repairing that costs ten times more than replacing a set of spark plugs. Based on my experience, spark plugs typically last 20,000-40,000 km under normal city driving conditions, and those frequently used in congested areas should be inspected even earlier.

[SanLena]

A simple calculation shows that not replacing them actually costs more: Worn spark plugs can increase fuel consumption by at least 15%. Based on 20,000 km per year, that's an extra 300 liters of fuel, costing over 2,000 yuan annually. A set of ordinary spark plugs only costs a few hundred yuan. If ignition failure damages the ignition coil, repair costs double immediately. I've personally seen a car with stuck piston rings due to un-replaced spark plugs, requiring an engine overhaul costing tens of thousands. It's recommended to have the ignition voltage checked during every minor maintenance and replace if it exceeds the standard.

[McSarah]

Last winter, I experienced the embarrassing situation of the car not starting, all because the spark plugs had reached the end of their lifespan. Especially in sub-zero temperatures or rainy weather, aging spark plugs are more prone to failure. A sudden misfire on the highway is even more dangerous, causing the car to jerk and shudder while driving. After that incident nearly made me miss an important meeting, I now make it a rule to replace the spark plugs every two years without fail. Don’t think you can get by just because the car still starts—delayed ignition might leave you stalled at an intersection with honking cars behind you, and failing to start in freezing weather can lead to even bigger troubles.

[SanLouis]

Delaying spark plug replacement first affects driving quality: idle vibration feels like a massage chair, and acceleration during overtaking becomes sluggish. Secondly, it leads to pungent and unpleasant exhaust fumes, with the dashboard warning light illuminating. Prolonged neglect can cause exponential carbon buildup in the engine, potentially resulting in knocking that damages the cylinder block. During one engine disassembly, I observed pits burned into the piston crown caused by poor ignition. I generally recommend using OEM-spec spark plugs, as aftermarket high-performance ones may prematurely wear out the ignition coils.