Iridium spark plugs have become very popular in the last couple of decades, providing superior performance and longevity compared to standard copper plugs. However, with advancements in technology, many people wonder if old iridium plugs from the 90s and early 2000s are still worthwhile or if they should be replaced.
How do iridium spark plugs work?
Iridium spark plugs work the same way as standard copper spark plugs, using a spark to ignite the fuel/air mixture in the engine’s cylinders. The difference lies in the material used for the center electrode and ground electrode.
In a standard copper spark plug, the copper center electrode wears down over time, resulting in a wider gap between the electrodes. This makes it harder for the plug to produce a spark. The electric current takes the path of least resistance and may travel outside of the gap, causing misfires.
Iridium is 6 times harder and 8 times stronger than copper. It resists wear and has a melting point of about 4,700°F compared to copper’s 1,984°F. This allows the gap between the iridium center and ground electrodes to remain narrow even after extensive use, promoting better sparking and combustion.
Advantages of iridium spark plugs
- Last longer – Up to 60,000 miles compared to 20,000 for copper plugs
- More powerful spark for better combustion and power
- Better performance at high speeds/loads
- More stable sparking in cold weather conditions
- Resist fouling and corrosion better
Do old iridium spark plugs need to be replaced?
Iridium spark plugs definitely last longer than copper plugs. However, there are a few factors that determine whether you need to replace old iridium plugs or not:
1. Vehicle mileage
As mentioned earlier, iridium plugs can last for 60,000 miles or more. If your vehicle has crossed this mileage with the old plugs, it’s a good idea to replace them.
2. Engine problems
Issues like rough idling, power loss, poor acceleration, or fuel efficiency drop can indicate worn out spark plugs. If you face any such problems, replacing the iridium plugs can help, even if the mileage is less.
3. Condition of the plugs
Physically examine the old iridium plugs. Look for excessive wear on the electrodes, corrosion, deposits, cracks in the insulator, etc. Severely worn out plugs won’t fire properly and create performance issues.
4. Tuned/modified engines
Aftermarket modifications like turbochargers, superchargers, nitrous oxide, high-lift cams, or engine tunes can increase combustion pressures. This accelerates spark plug wear. Plugs may require earlier replacement in modded engines.
Are there any downsides to using old iridium plugs?
Old iridium spark plugs may work well if they are in good condition. However, pushing them beyond their service life can cause problems like:
- Misfires and poor combustion
- Power and acceleration loss
- Increased emissions
- Fuel efficiency drop
- Difficult cold starting
- Fouling of plugs
- Engine knock or pinging
Worn out plugs increase the risk of engine damage too. Replacing plugs at the recommended intervals ensures optimum engine performance and longevity.
Do iridium spark plugs go bad over time?
Yes, even though iridium plugs last longer, they do deteriorate over time. Here are some ways in which iridium plugs can go bad:
- Electrode erosion – Repeated sparking wears down the iridium electrodes over time.
- Corrosion – Rust accumulation on the electrodes hampers conductivity.
- Lead fouling – Buildup of lead deposits from leaded fuels.
- Oil fouling – Carbon deposits from engine oil covering and insulating the plug tip.
- Insulator cracking – Thermal shocks and mechanical damage can crack the insulator.
These factors impair the plug’s ability to ignite the air-fuel mixture. If left unchanged, it can lead to misfires, power loss, and poor engine performance.
What are the typical service intervals for iridium spark plugs?
Here are the typical iridium spark plug replacement intervals for different vehicles:
| Vehicle Type | Replacement Interval |
|---|---|
| Passenger cars | 60,000 – 100,000 miles |
| SUVs and trucks | 45,000 – 75,000 miles |
| High performance vehicles | 35,000 – 55,000 miles |
| Modded/tuned engines | 15,000 – 30,000 miles |
However, keep an eye on engine performance and replace the plugs immediately if you face any issues, regardless of the mileage.
What affects the lifespan of iridium spark plugs?
There are several factors that impact how long iridium spark plugs will last in an engine:
Driving style:
Aggressive acceleration and high speeds can cause early wear of plugs. Gentle driving extends plug life.
Type of driving:
Short trips and excessive idling lead to more oxidation and fouling issues compared to highway cruising.
Engine temperatures:
Excessively high temperatures due to factors like timing issues, wrong spark plug heat range, or lean mixtures can deteriorate the plugs prematurely.
Tune-ups:
Regular tune-ups with proper gapping and cleaning of contacts help maximize plug service life.
Oil consumption:
Engines burning more oil foul the spark plugs faster, necessitating early replacement.
Fuel quality:
Low-quality fuels can form harmful deposits on plugs, affecting their performance and longevity.
Do iridium plugs need to be replaced in pairs?
It is generally recommended to replace iridium spark plugs in pairs on engines with separate coil packs for each cylinder. Some reasons for paired replacement include:
- Avoiding power imbalance between cylinders
- Preventing increased strain on new plug
- Restoring uniform performance across engine
However, you can also replace plugs individually if only one is worn out. Make sure to match new plug to old one’s heat range and specifications.
Can worn iridium plugs cause engine damage?
Yes, running an engine with worn out or fouled iridium spark plugs can potentially lead to costly damages like:
- Detonation and pre-ignition damage to pistons or cylinder head
- Melted electrodes destroying the engine’s combustion chamber
- Fouling causing exhaust valve failure
- Improper burning of fuel leading to carbon buildup
- Lean fuel mixtures overheating and warping engine parts
In worst cases, severely worn plugs can cause power loss and stalling, especially at high speeds, increasing the risk of accidents.
Are there any alternatives to iridium plugs?
Some alternatives to iridium spark plugs include:
Platinum plugs:
Also last longer than copper but not as durable as iridium. Better for lightly modded engines.
Ruthenium plugs:
Provide superior durability and service life than platinum but are more expensive.
Silver or nickel-alloy electrodes:
Cheaper than exotic metals but don’t last as long in high-performance applications.
Double platinum plugs:
Platinum both on the center and ground electrode for increased longevity.
Is it worth buying used/refurbished iridium plugs?
It’s generally not recommended to use used or refurbished iridium spark plugs. Some concerns regarding used plugs include:
- No way to ascertain accurate vehicle mileage or engine run time
- Potential for worn electrodes or insulation failure
- Lack of performance testing or calibration data
- Problems caused by improper cleaning methods
- No guarantee or warranty on used plugs
Unless sourced from a very trustworthy supplier, the minor savings don’t justify the risks of using used iridium plugs.
What are the signs of worn out iridium plugs?
Here are some common indicators that your iridium spark plugs may be past their service life:
- Rough idle, engine misfire, hesitation or loss of power
- Increased fuel consumption and emissions
- Difficulty starting the engine, especially when cold
- Soot deposits around the plug’s insulator tip
- Corroded, cracked, or damaged insulator
- Severely eroded electrodes with an overly wide gap
If you notice any of these warning signs, get your spark plugs inspected or replaced immediately to restore peak engine performance.
Conclusion
While iridium spark plugs have excellent durability, they do need replacement after prolonged use. Very old iridium plugs from the 90s/early 2000s should be changed if they have over 60,000 miles of usage. However, the lifespan also depends on specific engine conditions and driving habits. Replacing worn plugs at proper intervals is crucial, both for optimal performance and preventing engine damage. Using new OEM iridium plugs is highly recommended for reliability. With proper maintenance, they will provide many miles of smooth and efficient engine operation.