This may be pre-mature but does anyone think changing spark plugs, before their supposed 100,000 mile life expectancy, will improve their gas mileage? If you do agree, what would the cost per plug be if you did it yourself ?

 

Highly-highly unlikely. We've had three cars cross the 100,000 mile mark, and two of them have crossed the 200,000 mile mark in recent years. We keep detailed fuel economy records of all of our cars, and not one of the five plug service events resulted in improved fuel economy by any measurable degree. To take it a step further, when the last of our cars crossed the 100,000 mile threshold I was very busy and didn't get to the plugs until 125,000 miles, and even then there wasn't even a .01% improvement in fuel economy.

Think about it this way, modern ignition systems generate so much power that even of the plug gap is 25% wider than when new, the spark is so aggressively hot and robust that it really won't make much of a difference at all in how the car runs, its relative power, or its relative fuel economy.

 

Thanks for your feedback and quick response shipo.