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A Guide To All 4 Spark Plug Types (And How They Compare)

January 18, 2022

Spark plugs are a vital piece of the ignition system in an internal combustion engine. 

The metal used in a spark plug electrode influences its longevity and performance — which, in turn, can affect fuel economy and fuel efficiency. 

Today, you’ll typically find copper, iridium, and platinum spark plugs for vehicles.

So, how do these spark plug types differ, and can you use them in your car?
This is what we’ll talk about in this article. 

First, we’ll cover why the metal used on a spark plug electrode is important
Then, we’ll examine common spark plug types: copper, platinum, double platinum, and iridium. And finally, we’ll see how these spark plugs compare.

This Article Contains:

Let’s get revving.

Why Is The Type Of Spark Plug Electrode Important?

At the tip of a spark plug are two metal electrodes — called the center electrode and ground electrode. Electricity arcs between these electrodes, generating a spark that ignites the air-fuel mixture in an engine’s combustion chamber.

Most spark plugs feature a copper core central electrode. 
That’s because copper is one of the best electricity conductors and transfers heat faster. 

Now, with so much heat generated with each spark, imagine what it does to the electrodes?

Remember, copper is soft and has a low melting point. 

To reduce wear from high voltage sparks, stronger metals like nickel alloy, or a precious metal like platinum or iridium, are used to coat the electrode tips. Using these metals helps to extend spark plug life and improve performance.

Here’s a closer look at two factors influencing spark plug performance:

Spark plug performance also impacts your vehicle’s fuel efficiency and fuel economy, as faulty or dirty fouled spark plugs can cause problems like cylinder misfires or partially burnt fuel.

Now, let’s look at the standard spark plug. 

Copper Spark Plugs: The Standard Spark Plug

When people mention a standard spark plug, they’re likely referring to the copper spark plug. Copper spark plugs are the oldest type of spark plugs with a copper core.

Recall how copper has a low melting point? 
Despite the name, electrodes on copper plugs aren’t fully copper. 

They have a nickel alloy fused to the electrodes, typically 2.5mm diameter, to reinforce durability. This is the largest electrode diameter of all spark plugs, which means copper spark plugs draw more current than other types to produce a spark. 

The nickel alloy on copper plugs isn’t as hard as other metals, so it wears faster under the high heat and pressure in the engine’s cylinders. This will eventually lead to dirty fouled spark plugs that don’t perform optimally. 

Its shorter lifespan means the copper plug typically needs replacement every 20,000 miles or so

So, is the copper spark plug widely used?
Yes. It’s the most commonly available and cheapest spark plug around. 

You’ll find it in older, pre-1980s vehicles with distributor-based ignition systems. And because a copper plug can run cooler while providing plenty of power, you may find it in late-model turbocharged engines or engines with higher compression ratios. 

However, don’t use copper plugs in coil-on-plug ignition systems or high-energy distributor-less ignition systems as they’ll wear too fast. 

Also, if your vehicle owner’s manual calls for copper spark plugs, don’t upgrade to iridium spark plugs or platinum spark plugs.

Next, what are platinum spark plugs?

Single Platinum Spark Plugs: An Excellent Middle Ground

A single platinum spark plug is like a copper spark plug but has a platinum disc fused to the centre electrode instead of a nickel alloy. 

Platinum is much harder, with a higher melting point than nickel alloy. This allows a platinum spark plug to retain a sharp edge (and resist wear) much longer. 

Longevity is a key advantage in platinum spark plugs — they’re typically replaced around 60,000 miles but can last up to 100,000 miles. And because platinum can handle a high heat range, combustion deposits burn off better, preventing spark plug fouling.  

However, platinum is less conductive than copper, so the platinum spark plug suffers a little in performance compared to copper spark plugs. 

Where is the platinum plug used?
Platinum spark plugs are often used in newer vehicles with electronic distributor ignition systems. 

And here’s another thing — if your OEM plug is a platinum spark plug, don’t downgrade to cheaper spark plugs like copper. You can, however, upgrade to double platinum spark plugs or iridium spark plugs.

We now know about the single platinum spark plug. 
What about double platinum? 

Double Platinum Spark Plugs: For Waste Spark Systems

The double platinum spark plug is just like a single platinum plug, except it has a platinum disc on both the center and ground electrodes.

Double platinum spark plugs were designed for “waste spark” systems. 

In waste spark systems: 

The spark is “wasted” because nothing ignites on an exhaust stroke (as it removes combustion gases).

Single platinum spark plugs or traditional copper plugs won’t work for these systems as they aren’t designed to handle the reverse spark. So, if your vehicle uses double platinum spark plugs, then that is the best spark plug for your car. 

An alternative would be to upgrade to an iridium-platinum combination plug (with an iridium central electrode with a platinum ground electrode).

Finally, let’s look at the iridium plug.

Iridium Spark Plugs: Long Lifespan Spark Plugs

Iridium is about 6 times harder and 8 times stronger than platinum, with a melting point over 1200°F higher. Thanks to this combo of characteristics, the iridium plug can last up to 25% longer than platinum spark plugs.

That said, even iridium spark plugs can’t compare to the superb conductivity of copper plugs. There are, however, other advantages. 

As iridium is costly but strong, manufacturers can reduce the center electrode of the iridium spark plug down to 0.4mm. On top of reducing cost, this “fine wire” center electrode on this plug also requires less voltage to generate a spark, thus increasing firing efficiency.  

You can easily tell iridium spark plugs apart by their narrow center electrode tip. Many iridium spark plugs also feature a shaped channel on the ground electrode, which prevents the high voltage spark from quenching. 

The iridium plug can generate a higher flame quality, creating a more concentrated spark. This allows the iridium spark plug to power engines faster than other plug types, and burns fuel more efficiently. 

In fact, the only real downside to iridium spark plugs is their cost, as iridium is pretty expensive.

So, where are iridium spark plugs used?
You’ll often find them in the coil-on-plug (COP) ignition system. If your vehicle requires iridium spark plugs, don’t downgrade to cheaper spark plugs as they won’t suit your engine.  

If you’re curious, the iridium NGK spark plug or Bosch spark plug are some of the popular iridium plugs on the market.

Note: We’d be remiss, not to mention the silver spark plug. The silver spark plug is a fine thermal conductor but doesn’t last as long as the platinum or iridium plugs, so it’s not commonly used today. You’ll find silver plugs in older European cars or motorcycles.

Now that we’ve gotten down the basics on spark plug types, let’s now see how they stack up against each other.

How Do Copper, Iridium, And Platinum Spark Plug Types Compare? 

Let’s compare copper, iridium, and platinum spark plugs on three aspects — longevity, performance, and cost:

A. Longevity

Platinum is harder than copper, but iridium is the hardest among the three metals. 

The average annual mileage of vehicle owners in America is around 13,476 miles. Referring to this number, we can say that:

So, if you don’t want to worry about spark plug replacement for a long time, iridium might be the way to go. But if this expensive spark plug deters you, platinum spark plugs may offer a balanced middle ground between cost and longevity.

B. Performance

The copper spark plug offers the best performance simply because copper is a fantastic electrical conductor and runs a little cooler. 

An iridium spark plug delivers better performance than platinum but is impacted by high cost. 

And if performance is a significant selection factor for you, you may want to skip the platinum spark plug section.

Note: If you’ve heard of a hot or cold spark plug, it refers to the plug’s insulator tip, not electrode metal. A cold spark plug has a shorter insulator tip to dissipate heat from the combustion chamber quickly. A hotter plug has a long insulator tip, so the firing end heats up faster.

C. Cost

Copper spark plugs are the most economical with great performance, but they do draw more battery voltage than other plugs.

Platinum spark plugs are more costly than copper plugs but cheaper than iridium plugs and offer a good life cycle. 

Iridium is the most expensive spark plug, but offers good performance and a great lifespan as long as the cost isn’t an issue.

As a final note, always check your owner’s manual or consult your mechanic if it’s viable to change spark plug types.

Closing Thoughts

Whether your car uses copper, iridium, or platinum plugs, always get quality spark plugs to replace your worn spark plugs. 

An OEM plug is an excellent option as it’ll match what’s already in your engine, but it does tend to cost more than an aftermarket spark plug.

However, if thinking about a new spark plug is too much of a hassle, you can always get help — and RepairSmith is just a few clicks away!

RepairSmith is a mobile vehicle repair and maintenance solution, available 24/7, whether for a spark plug replacement, cylinder head problem, or some other vehicle issue. 

Not only will our expert mechanics change your spark plugs, but they’ll also ensure that your spark plug wire is damage-free, the spark plug gap is correct, and everything is in good condition.

Contact us, and our mechanics will drop by your driveway to lend a hand in no time!