Spark plugs may become less effective at doing their job due to time, wear, or other electrical/ignition system issues. They may become "fouled" over time due to combustion, contamination, or overheating, losing their ability to spark the air-fuel mixture and dissipate heat away from the combustion chamber.
Age and Mileage
Plugs are designed for long-term durability, and could well outlast your car. However, they experience wear with engine use and are more vulnerable to car usage than to age, so mileage is an important factor when thinking about a replacement.
Even if you're not having problems, you'll still want to change spark plugs out at every 30,000-mile interval. For most drivers, that will mean that you're due for spark plug service once every 2-3 years!
Spark plugs deteriorate over time. Your car may face loss of engine power, fuel efficiency, or problems with combustion. At some point, you risk spark plug failure, and your car simply won't start. As you drive, your spark plug gap opens up from damage and carbon fouling.
FACT #4: YOU SHOULD CHANGE SPARK PLUGS EVERY 100K MILES OR SO. So, if good spark plugs are the key to avoiding these issues, how long do spark plugs last, exactly? The general rule of thumb about how often to change spark plugs is that they should be replaced after about 100,000 miles of driving.
Luckily, spark plugs don't require replacement very often and can go years and many miles before replacement is needed.
Ordinary copper and nickel spark plugs should be changed every 30,000 to 50,000 miles, unless otherwise suggested by the spark plug manufacturer. Platinum and iridium spark plugs tend to last longer than standard copper and nickel spark plugs. Expect to change them every 60,000 to 150,000 miles unless otherwise noted.
Standard copper spark plugs last around 20,000 – 30,000 kms. The spark plugs play an important role in your engine, they produce electrical sparks that ignites the mixture of fuel and air in your engine's combustion chambers, causing the pistons to move up and down.
Many factors can cause a spark plug to fail; from incorrect heat ranges to improper gapping, to chemical contamination. Yet 90% of spark plug damage claims are due to improper torque. Many factors can cause a spark plug to fail; from incorrect heat ranges to improper gapping, to chemical contamination.
A leading cause of spark plug problems is a flow of engine oil into the combustion chamber. If oil leaks into the combustion chamber, it can cause the tip of the spark plug to get oily and dirty leading to premature failure.
Most manufacturers recommend replacing spark plugs every 50,000 kilometres, but spark plug quality varies. Some last around 130,000 kilometres, while cheap plugs made of copper may last approximately 40,000 kilometres. “Extended life” spark plugs made of more resilient metals can last up to 160,000 kilometres.
Spark plugs are designed for long-term durability, meaning that they only need to be replaced between every 80,000 and 100,000 miles. However, they can become damaged earlier than expected and require replacements to avoid pricey engine repairs.
If money is tight, keep them in as it likely won't hurt, but if you plan to keep the car long-term, I say do them because after 10 years, it's an opportunity to make sure the rear valve cover isn't leaking, and with a new set of spark plugs, you could prep them with some anti-seize lubicant on the threads, and then you ...
Heat Damage
Overheating, often caused by poor ventilation and a lack of exhaust dissipation, causes internal damage to metallic spark plugs that can greatly reduce their lifespan. Excess heat also generates a build-up of fractured iron and carbon deposits, increasing resistance.
Platinum is much harder metal than nickel alloy and has a higher melting point. Since platinum is harder, it holds its sharp edge much longer than a conventional spark plug, up to 100,000 miles. Longevity is a key advantage of platinum spark plugs.
While a typical iridium spark plug can last for 50,000-80,000 miles, manufacturers set different limits for these plugs based on driving conditions. For example, NGK's Iridium IX spark plugs claim a 40,000-50,000 miles life expectancy on an unaltered motor.
The spark plugs in many vehicles today have iridium or platinum tips on the electrodes (the parts that transmit the spark) that last longer than conventional plugs with copper and nickel-alloy electrodes.
The deposits that build upon the plugs can eventually cause them to misfire. When this happens, the unburned fuel in the cylinders can start to eat away at the cylinder walls. This can cause dangerous pressure levels to build up, and it can even lead to engine failure.
Over time, they get worn or build up deposits from years of use and they become less effective and efficient. I have rarely ever heard of a spark plug failing 100% all of a sudden. Over time, it would contribute to reduced gas mileage, rough idle, and sluggish performance.
An old spark plug can cause rough idling, engine idling, and poor acceleration. You'll also notice that worn spark plugs have a wider spark plug gap due to wear. This, in turn, interrupts the consistent combustion system leading to rough idling, poor acceleration, and engine misfire.
In most cases, you'll see a noticeable difference in performance after replacing your spark plugs and wires. The engine will run smoother and faster, and the car will have better acceleration. You may also notice an improvement in fuel economy.