Are OEM Spark Plugs Worth It? - Toyota Parts Blog

Spark plugs aren’t made to last forever. When they eventually need replacement, the options are:

  1. Buy whatever the local auto parts store has
  2. Buy a genuine OEM replacement

Should you go for OEM quality or a less expensive set of after-market plugs? We may be biased, but we think there’s only one answer to this question (go OEM). If you read about why we feel OEM plugs are best below, we think you’ll agree.

Toyo spark plugs

The Anatomy of an OEM Plug

It’s hard to tell an OEM plug apart from an after-market plug, but that’s because it’s hard to see the difference with your eyes. The difference is in the materials and the specs of each component. Here’s what goes into a standard Toyota OEM spark plug:

Quality Ceramic Insulator – The role of the insulator is to insulate the terminal studs and central electrode from the plug’s shell. If the insulator quality is poor, it will fracture during installation or when temperatures rise. Poor quality insulators are cheap, however, which is why they’re often used on after-market plugs.

Nickel-Plated Plug Shell – The metal casing around the shell which both protects the plug and is used to secure the plug in the cylinder head. A quality OEM plug has a nickel-plated steel shell, as nickel is both corrosion resistant and unlikely to cause a plug to seize in the threads on the cylinder head. Many after-market plugs use a very thin nickel coating or omit it altogether to save money.

Platinum or Iridium Center Electrode – OEM Toyota plugs either have a platinum tip (90k mile lifetime rating) or an iridium tip (120k mile lifetime rating). Platinum and iridium are both costly metals, and one of the easiest ways to cut costs on a spark plug is use a low grade of platinum or iridium. That’s precisely what a lot of cheap spark plug manufacturers do.

Quality Interference Suppression Resistor – Spark plugs generate a lot of electromagnetic signals when they fire, and these signals interfere with the electronics in modern vehicles. The solution? An interference suppression resistor inside each spark plug, which keeps these signals/electronic “noise” from interfering with the proper function of various electronic parts in your vehicle.

A plug with cheap interference suppression resistor will cause static on your stereo speakers, potentially effect your vehicle’s navigation system, and can also impact key electronic sensors like ABS wheel speed sensors, crank position sensors, and more. Many after-market companies go with a simple, cheap interference suppression resistor and hope your vehicle isn’t sensitive to the subsequent electrical noise.

Precise Fitment and Dimensions on the Plug Body and Electrodes – Engine tolerances are tighter than ever, meaning that a spark plug must have a precise length. A few hundredths too long, and the plug electrodes can interfere with the valves or pistons. A few hundredths too short, and combustion is incomplete. One of the easiest ways for manufacturers to save money is to reduce tolerances, and usually the cheap after-market plug companies hedge towards plugs that are too short rather than too long. This reduces combustion efficiency.

OEM plugs, on the other hand, are precisely uniform in length. They’re also precisely uniform in electrode size, shape, and gap.

OK, So OEM Plugs Are Better. Why Should I Care?

In a word, fuel economy (OK, that’s two words). Cheap plugs don’t last as long either, but it’s really the fuel economy that will cost you.

If, for example, your after-market plugs don’t have the same high grade platinum or iridium tips, don’t have the same precise spark gap, electrode profiles, or are a bit too short, your fuel economy will decrease. While the decrease isn’t tremendous (we’re talking 1-2% here), the decrease adds up. If you have an average car that gets about 24mpg, and you drive 15,000 miles a year and pay $3 for a gallon of gas, a 2% decrease in gas mileage will cost you and extra $37.50 at the gas pump this year.

If you were to use cheap spark plugs for the next 3, 4, or 5 years, you’d waste $100-$200 on gas. When you compare the cost of a cheap set of spark plugs to a set of quality plugs bought online, there is no savings…Not to mention, your cheap plugs might not last 3, 4, or 5 years before they need replacement.


When you use OEM plugs, you’re using the plug made to help your Toyota’s engine perform at its best. While they’re a little more costly than most after-market brands, they’re precisely engineered for your engine. They will maximize fuel efficiency and save you hundreds of dollars at the fuel pump!

Written by Elizabeth Puckett