Engine & warning lights
Spark Plugs: Types, Lifespan, and Reading Engine Health From Them
Copper, platinum, or iridium — and what a plug's appearance reveals about deeper engine faults.
The short version
$10–32 per plug by type, plus $27–110 labour depending on access.
- 4 symptoms you can check yourself
- 4 diagnosis steps in order
- 2 FAQs answered directly
- Last editorial review: 2026-08-01 · 5 min read
The problem in brief
Plugs are cheap parts that tell the engine's whole story. Tip colour and condition reveal oil burning, rich mixture, and overheating before any code appears.
Root technical cause
- Past service life: copper 20k mi, platinum 40–50k, iridium 55–75k
- Incorrect electrode gap
- Oil burning fouling the tip
- Wrong heat range for the engine
Real-world symptoms
- Slow starting and weak acceleration
- Higher fuel use with a light stumble
- Repeated misfire codes
- Idle vibration
How it is repaired correctly
- Pull one plug and read the tip: light brown = healthy, dry black = rich, white = overheating
- Verify gap with a feeler gauge before fitting
- Torque to specification to avoid stripping threads
- Replace the full set, never a single plug
Reducing the chance of recurrence
Avoid counterfeit plugs — the price gap is small and the damage to coils is not.
What to expect to pay
$10–32 per plug by type, plus $27–110 labour depending on access.
Figures are a guidance range calculated with a published method — read the methodology.
Q&A
Is iridium worth the premium?
Yes on modern engines: three times the life and far more stable spark.
Only one plug failed?
Replace the whole set so cylinders stay balanced.
DriveMet review
$10–32 per plug by type, plus $27–110 labour depending on access. Avoid counterfeit plugs — the price gap is small and the damage to coils is not.
What we verified
- Cross-checked 4 warning signs against 4 likely causes before publishing.
- Reviewed 4 repair steps and confirmed the order a shop would follow.
- Compared the cost range with our published methodology and refreshed it on 2026-08-01.
- Answered 2 questions people actually search for on this topic.
Reviewed by the DriveMet editorial team on 2026-08-01 under our editorial policy. This is an editorial review of the page, not visitor ratings.
Related tools
Apply what you just read to your own car with your own numbers.
Reference sources
- NHTSA vPIC — vehicle specifications and manufacturer recalls
- EPA fueleconomy.gov — reference fuel-economy figures
- SAE J1979 standard for generic (Pxxxx) fault-code definitions
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