Are OEM Spark Plugs Worth It?

The spark plugs inside your GM’s engine aren’t designed to last forever. When it comes time to replace them, you might be wondering if OEM replacements are worthwhile or if you should go with a set of aftermarket spark plugs instead. There are a slew of differences between OEM and aftermarket spark plugs. Here's what you should know.

OEM spark plugs worth it

Cheap Spark Plugs Can Be Trouble

Most aftermarket spark plugs are made to be as cheap as possible. That's because the companies that sell cheap plugs assume that their customers won't know what makes one set of spark plugs different from another. They assume consumers will just buy the cheapest plugs and move on.

But there are a lot of problems with cheap spark plugs - all of which are prevented by installing a higher quality plug. Here's how cheap spark plugs and high quality plugs are different:

The quality of the materials that make up the plugs. Generally, the materials used in low cost spark plugs are lower grade than OEM plugs. Most genuine GM plugs, for example, are tipped with a high purity platinum-iridium alloy and feature nickel-coated threads. Why does this matter?

  • The iridium-platinum alloy on the plug tip protects the plug from wear while it sits inside your engine's combustion chamber, exposed to literally millions of explosions. If the alloy isn't as pure or applied with sufficient thickness, the plugs don't last.
  • Nickel coating on the plug threads ensures easy removal after 100k miles. It's a little thing, but it could save you a big expense later if you need to drill out a cheap after-market plug that broke off in the cylinder head.

Additionally, the ceramic insulators in aftermarket plugs are usually far more fragile than the OEM ceramic insulators. This is another small thing, but it's not unheard of for these insulators to break on cheap plugs, ruining the plug and forcing you to replace it prematurely.

Plug fitment and gap inconsistencies are a risk. Aftermarket plugs that are even just a tiny little bit longer or shorter than your original plugs can rob power and fuel economy — even by just being off a few hundredths. If they're off even further, they can potentially cause engine damage.

The tolerances in the combustion chamber are incredibly tight on modern vehicles, and many after-market plug manufacturers don't want to invest in building a part to a very tight tolerance. Instead, they just make sure the plugs aren't too long, which results in an average plug length that's shorter than you need. This reduces combustion efficiency and increases your gas mileage.

Electrode design and shape matter a lot! OEM spark plug electrodes are carefully crafted to a very specific shape — adding complexity and cost to the process. This is an area where aftermarket suppliers like to cut corners, and that’s not good. It’s this shape that maximizes performance of your vehicle — determining the efficiency of the combustion event. OEM plug makers take great measures to make sure to pair the electrode with the engine its intended to go in — going to a cheap blade design will cost you power and fuel economy.

Still Want to ‘Just Save Money’? You Aren’t.

Let's pretend that you're only interested in saving money up, or maybe that you don't care if your spark plugs last 100k miles. "Why should I invest in a great plug if I'm going to get rid of this car next year?"

Because inferior plugs cost you at the gas pump.

Cheap spark plugs aren't made to factory tolerances, don't use the same high grade alloys, don't feature the same electrode design, etc., and that all adds up to a decrease in fuel efficiency. If the plugs only hurt your fuel economy 2%, they'll cost you $3 a month in wasted gas (based on the average fuel expense per vehicle in the USA). After 12 months, that's almost $40 in wasted gas. Over five years, saving money on spark plugs can be very expensive.

Basically, whatever you save up front with aftermarket plugs will come out of your wallet at the gas pump.

The OEM Difference

There are many benefits to using OEM spark plugs, including:

  • Longer service life
  • Greater spark plug efficiency
  • Greater energy with ignition sparks
  • Higher wear resistance
  • Better resistance to chemicals in the combustion chamber
  • Greater resistance to material erosion
  • Perfect flame dispersion front on all sides

When you use OEM plugs, you get an assurance of quality that you don’t get when you use cheap aftermarket parts. If you’re trying to save money, cheap aftermarket spark plugs aren't the way to do it.