Bad Fuel Economy? Your Spark Plugs Might Be the Problem

If your gas mileage has been declining gradually, worn spark plugs could be a significant contributor. It's a subtle problem that many drivers don't connect to their ignition system — here's the explanation.

How Spark Plugs Affect Fuel Economy

Worn spark plugs don't fire as efficiently. The spark becomes weaker or inconsistent, leading to incomplete combustion. When fuel doesn't burn completely in the cylinder, it's wasted — your engine needs more fuel to produce the same power output, which means lower MPG.

Studies have shown that worn spark plugs can reduce fuel economy by up to 30% in severe cases. More typically, you might lose 5–10% over the life of a set of plugs before they're fully worn out.

Other Symptoms That Often Accompany MPG Loss

• Slightly rougher idle
• Sluggish acceleration (especially from a stop)
• Engine hesitation on hill climbs
• Check engine light (may or may not be present)

How to Test the Theory

Track your fuel economy over 3–4 fill-ups, noting miles driven and gallons used. Replace your spark plugs and track the same data for 3–4 more fill-ups. Many owners report a measurable improvement in MPG after a fresh set of iridium plugs.

Other Fuel Economy Culprits

While you're at it: also check your air filter, oxygen sensors, and tire pressure. These are all inexpensive items that significantly impact fuel economy when neglected.

Shop fuel-efficient iridium spark plugs at Texan Supply with free shipping.