Simple parts make a big difference in the way your vehicle performs and the kind of gas mileage it gets. For instance, something as mundane as a spark plug can dramatically affect engine performance.
“Spark plugs can misfire at some engine speeds and may be the culprit if your vehicle’s fuel economy drops suddenly,” said Tony Molla, vice president of communications for the National Institute for Automotive Service Excellence. “Usually, spark plugs don’t need a lot of maintenance.”
Spark plugs have performed the same basic function since they became commercially available more than a century ago. Simply put, they transfer energy from the vehicle battery to the combustion chamber and ignite fuel that moves the piston.
Gasoline-powered vehicles use spark plugs but not diesel engines.
“Every time the spark plug ‘fires,’ or ignites fuel in the engine, it corrodes the small metal components at the bottom of the plug,” Molla said. “How often you need to replace vehicle plugs depends on the type of vehicle, type of spark plug, how often you drive and the driving conditions.”
Traditionally, plugs made of copper needed to be replaced every 15,000 miles or so. Today, factory-installed equipment generally includes platinum spark plugs and have an expected lifespan of about 100,000 miles.
“Recommended replacement varies from one model to another,” Molla said, “Drivers should look at their owner’s manual to see the rating for spark plugs used in their specific vehicles.”
Most modern engines often have aluminum cylinder heads and use spark plugs made of steel. The various metal components expand at different rates. As a result, plugs can become stuck and the replacement procedure tricky to avoid damaging the threads in the cylinder head.
It’s also usually necessary to coat the replacement spark plug threads with an anti-seize compound to avoid problems down the road.
“The compound helps prevent expensive damage to the softer metal of the cylinder heads,” Molla said. “Always ask your service advisor what type and brand of spark plug they recommend for your specific vehicle.”
All manufacturers use different kinds of plugs. Some have longer electrodes than others. If you use one that’s too long for your car, the electrode can reach too far into the cylinder and interfere with the piston.
What about replacing spark plug wires?
“Spark plug wires are being phased out of new cars much the way points and condensers were replaced by electronic ignition." Molla said. “If your vehicle does have spark plug wires, ask your service advisor to check their condition and recommended replacement mileage.”
Spark plug wires are copper or another conductive material wrapped in a protective sheath. They transfer electrical current from a coil and/or distributor. High voltages going through spark plug wires tend to deteriorate the wires over time.
“Heat dries and cracks wire coatings, and that can dramatically affect vehicle mileage and performance,” Molla said. “The entire wire set should be replaced anytime you see a crack in a wire. Drivers have a lot of choices when it comes to replacement wires—from inexpensive thin copper wires to high copper strands wrapped in a silicon sheath."
Better spark plug wires generally perform better and last longer, Molla said. Molla had the following tips for changing your spark plugs and wires:
Spark plugs require routine maintenance like other engine parts. Check your owner’s manual or consult your service advisor for replacement intervals.
Driving conditions and use vary how often spark plugs need to be replaced. Frequent starting or stop-and-go driving can cause spark plugs to degrade faster than infrequent freeway travel.
Spark plugs vary by vehicle model. Check manufacturer recommendations to prevent engine damage.
Spark plug design varies. Generally, copper plugs are the least expensive and wear faster. Plugs made out of platinum or similar compounds offer longer lifespan.
Check spark plug wires for creaks and signs of deterioration. The newest vehicles do not contain spark plug wires, but operate with a coil-on-plug system that eliminates the need for conventional wires.
“Small items can add up to a big difference when it comes to engine performance and economy,” Molla said. “Spark plugs and spark plug wires can affect gas mileage and power.”