Rick's Free Auto Repair Advice

When to replace spark plugs

When to replace spark plugs

Know when to replace spark plugs

Your know-it-all friends don’t really know when to replace spark

when to replace spark plugs

Worn spark plug with rounded center electrode and excessive gap

plugs on your particular vehicle. Instead, they’ll tell you that spark plugs last at least 100K miles. Wrong!

Spark plug life depends on MANY factors including engine design, ignition system design, the type of plug recommended by the factory and whether the engine is equipped with a turbo. Since there’s no universal engine, there’s no such thing as universal spark plug life.

Spark plug life is listed in your maintenance guide

Never depend on word of mouth advice from your buddies. Here’s an example of how much the spark plug change intervals vary:

2010 Ford Fusion: Spark plug replacement at 90,000 miles

2013 Chevy Equinox: Spark Plug Replacement at 97,500 miles

2013 Subaru Forrester: spark plug replacement at 60,000 miles

2013 Toyota Camry: Spark Plug Replacement at 120,000 miles

Can you extend spark plug life?

Yes, but not without cost. Just like everything else in your car, if you neglect routine maintenance and extend the change intervals, you’ll pay a price in additional wear. When you reach 80% of the spark plug’s projected life, the spark plug electrodes are 80% worn. It’s at that point when spark plugs start to misfire. And those misfires cost you in terms of performance, efficiency and gas mileage. Worse yet, misfires cause carbon deposits in the cylinder head and can damage the expensive catalytic converter. So it’s NEVER a good idea to go longer than car maker recommendations.

Which plugs should you use?

ALWAYS use the same type of plug recommended by the car maker. If the car came equipped with fine wire iridium, you MUST use that same style to get the same life and performance. My preference is to stick with the same brand that was installed at the factory.

Replace spark plugs yourself?

Replacing spark plugs isn’t a hard job. But one thing has changed from the early days of DIY spark plug replacement: you now need a torque wrench. Over and under torqueing spark plugs is the number 1 cause of spark plug failure, which results in misfire and can even cause the spark plug to blow out of the cylinder head (taking the threads with it).

Spark plug torque is dramatically reduced in engines with an aluminum cylinder head. Where you could have gotten away with hand tightening on a cast iron head, doing the same thing on an aluminum head can cause serious and expensive damage. Trust me, your hands can’t tell the difference between 15 ft/lbs and 25 ft/lbs., so ALWAYS use a torque wrench.

For more tips on spark plug installation, see this post

©, 2018 Rick Muscoplat


Posted on by Rick Muscoplat

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