Rick's Free Auto Repair Advice

Spark plug replacement

Spark plug replacement

Pick the right spark plug replacement

When platinum spark plugs came out, some carmakers raised the spark plug change intervals to as long as every 100,000 miles. Unfortunately, that’s now become folklore that every engine can go 100,000 miles between spark plug changes. It’s not true and never was.

The spark plug change interval depends on the type of spark plug and the engine design. Many late model turbocharged engines require spark plug replacement as often as 40,000 miles, and that with iridium spark plugs!

Types of spark plug replacements

“Copper” spark plugs

Copper spark plugs have a nickel-fused center electrode and side electrode on an internal copper core. Copper offers the lowest electrical resistance so they’re preferred on some high-performance engines. They’re cheap, but they have a short life because the center electrode rounds off which increases the gap size, causing higher firing voltage and sometimes resulting in misfires.

Platinum spark plug replacement

In the mid-1980s carmakers switched to using precious metals close up of a platinum tipped spark plug on the tips of the spark plug electrodes. The whole point of using precious metals was to reduce the erosion (wear) caused by higher firing voltages. Platinum has a higher melting point than copper, so the center electrode maintained its sharp edge longer, which allowed spark plugs to remain in service for as long as 100,000 miles.

Double platinum spark plugs

Double platinum spark plugs contain a platinum-tipped center and side electrode. They were designed to provide longer life when used in waste spark distributor-less ignition systems where the spark in the fclose up of double platinum spark plugiring cylinder jumps from the center electrode to the side electrode and in the partner cylinder from the side electrode to the center electrode.

Iridium spark plugs and double iridium

In the mid-1990s, carmakers switched to a harder precious metal: iridium. Iridium has a much higher melting point (700 degrees higher than platinum) is 6 times harder than and 8 times stronger than platinum, and conducts electricity better than any of the other precious metals. Therefore, it lasts the longest. However, it has a price to match. Depending on the brand, iridium plugs run from $8-15 per plug.close up of electrodes on single and double iridium spark plugs

Ruthenium Spark plugs

Ruthenium spark plugs from NGK are the latest design. NGK claims their new RUTHENIUM HX™ spark plugs provide a more complete fuel burn than other precious metal spark plugs. They also claim quicker throttle response, smoother idle, and better cold starts.

Ruthenium has a high melting point 4233°F, slightly lower than Iridium. But when alloyed with other metals, it becomes much more resistant to corrosion and oxidation than current iridium and platinum alloys.

NGK Ruthenium spark plug tip designs

NGK Ruthenium spark plug tip designs

Spark plug replacement — Which plug to use

You can always upgrade to a better spark plug, but you should never downgrade.

Make sure you use a torque wrench to tighten spark plugs

Plug manufacturers used to recommend applying a small dab of anti-seize compound on the threads. Not anymore. Spark plugs these days have an anti-corrosive treatment that makes anti-seize obsolete. Unless specifically recommended by the spark plug manufacturer, do NOT apply anti-seize to the spark plug threads. If you do, you MUST reduce the torque setting on your wrench by almost 20%.

Over-or-under-torquing spark plugs in an aluminum engine can cause substantial damage

If you under-torque, the repeated compression cycles can loosen the plug and blow it right out of the hole—taking the threads with it. That can easily cost you $500-$1,000 to repair. Some torque specs are as low as 10-ft/lbs. So it’s really easy to over-torque them. Check your service manual or the spark plug manufacturer’s specs for the right torque.

If you over-torque, you can damage the threads in the aluminum cylinder head, and you can distort the metal spark plug shell and cause a leak between the shell and the porcelain.

Check the spark plug gap before installing

Some spark plugs come pre-gapped and the instructions on the box warn you not to re-gap. Follow those warnings. If there are not warnings and the gap on the plug isn’t right, adjust the gap using proper spark plug gapping tools.

Use a proper spark plug gapper tool

See this post on how to choose a gapper tool

© 2012 Rick Muscoplat

Posted on by Rick Muscoplat



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