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Spark Plugs

Rekindle the Old Spark: How and When to Replace Spark Plugs

Spankin’ new spark plugs can do wonders for your driving experience. They’ll help your engine start and run smoother, and might even boost your vehicle’s fuel economy. The condition of your spark plugs affects power output and even engine temperature and emissions levels. Fitting inside each cylinder of a gasoline engine, spark plugs produce the spark needed to ignite the gasoline-and-air mixture as the piston reaches the optimum spot in the cylinder.

How do I know when I need to replace my spark plugs?

On older cars, the general guideline was to replace spark plugs every 30 months or 30,000 miles. With today’s complex engines, it varies by vehicle make, model and engine. Your best bet is to consult your owner’s manual or your automotive professionals at Glenbrook Auto Parts or one of our NAPA Auto Care Centers.

Extended life sparks reportedly can maintain a proper gap for 100,000 miles. But even in the case of these long-lifers, experts say inspecting them at the 30,000-mile mark is a smart idea.

If you’re not quite at the recommended mileage but are experiencing one of more of the following, you may have faulty spark plugs :

  • Hard-to-start engine
  • Rough idle
  • Misfiring engine
  • Surging engine or uneven acceleration (car jerks and then slows down or continually starts and stops)
  • Increased fuel consumption
  • Lackluster acceleration

What parts do I need to replace my spark plugs?

  • New spark plugs – Replace the spark plugs for all cylinders at the same time.
  • Spark plug wrench or spark plug socket and ratchet
  • Spark plug gap gauge (aka feeler gauge)
  • Rag and brush
  • Torque wrench

Key DIY Tips

These steps, pulled from the detailed directions listed on our NAPA Know How Blog, will help you replace your spark plugs:

  • Pick the right plug. A spark plug’s central electrode normally consists of copper, nickel or chromium, but more durable and powerful types use platinum or iridium. Don’t upgrade without consulting your owner’s manual.
  • Remove. Pull the spark plug wire by grasping the wire’s boot, not the wire itself. For coil-on-plug wires, make sure to not damage the coil. Remove any debris with a brush and compressed air. Loosen the plug with a plug socket and extension on your ratchet. Once loose, disconnect the ratchet and finish the job by hand. Keep debris out by stuffing the plug hole with a shop rag.
  • Inspect. An old spark plug’s appearance offers an excellent diagnostic tool. Black soot might mean a too-rich fuel mixture. Black moisture signals an oil leak. Blisters or burnt spots on the insulator and electrode indicate an excessively lean fuel mixture, overheating engine, overly wide gap or timing issue.
  • Set the gap. The space between the electrodes the spark jumps across to ignite gas within the cylinder is called the “gap.” Determine correct gap by checking your owner’s manual and set it using a feeler gauge. The gauge’s hook will open the gap slightly if necessary. To narrow the gap, gently press the electrode down on a non-marring surface.
  • Install. Apply a light coat of oil from the engine-oil dipstick to the plug threads (avoid contacting the electrodes). Thread the spark plug by hand using the socket and extension, then finish up using your ratchet to tighten to the manufacturer’s recommended torque specs. Reinstall plug wires in the correct order.

What other repairs or maintenance should I do at the same time?

If you’re replacing your spark plugs as part of a routine maintenance schedule, you may also want to:

  • Inspect or replace your air filter.
  • Inspect or replace your fuel filter.
  • Inspect or replace your cabin air filter.
  • Inspect or replace your ignition wires (if applicable).
  • Consult your owner’s manual for additional recommended maintenance.

If you’re replacing spark plugs because one was faulty, consider what other parts may need to be replaced as a result. For example, if one plug was not firing, that cylinder would have been dumping raw, unburned fuel into the exhaust system. That could have damaged the oxygen sensors or catalytic converters. While we don’t recommend replacing those unnecessarily, it would be smart to have them checked out.

Remember, with Glenbrook Auto Parts in Glenview, you can save time by ordering your parts online and picking them up in the store. We’ll have them ready and waiting for you.

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