The spark plugs in your engine aren’t made to last forever. When they eventually need to be replaced, you can choose to either replace them with whatever the corner auto parts store has in stock, or you can replace them with genuine OEM GM plugs.
What’s the right choice? While we may have a bit of a bias, we believe that OEM plugs are the only way to go. If you read the information below, we think you'll agree. Here's what you need to know about GM spark plugs (and why after-market plugs are a bad investment).
The Anatomy of an OEM GM Spark Plug
If you put a set of aftermarket plugs next to genuine plugs on a parts counter, the untrained eye may not notice a difference. Aftermarket plug manufacturers count on this, they don’t want you to think there is a difference, but there are quite a few. The materials and construction are what set them apart, and here’s how:
Quality Ceramic Insulator: The purpose of the insulation is insulate the terminal studs and central electrode from the shell of the plug. If this insulator is of poor quality, it can possibly fracture during installation or when the temperature gets high. Low grade insulators are cheap, which makes them attractive to aftermarket manufacturers.
Nickel-Plated Plug Shell: The metal casing around the shell that protects the plug while securing it in the cylinder is nickel-plated steel. This is coated in nickel since it’s corrosion resistant and not very likely to seize in the threads of the head. Many aftermarket plugs use only a very small amount of nickel coating, or just omit it entirely.
Platinum or Iridium Center Electrode: OEM GM plugs have either a 90k mile platinum tip, or 120k mile iridium tip. These are both very costly metals and aftermarket manufacturers often use a low grade blend instead — resulting in a much shorter lifespan.
Quality Interference Suppression Resistor: Spark plugs generate a lot of electromagnetic signals as they fire, these signals can interfere with electronics in your car. A high quality OEM spark plug will have an interference suppression resistor inside the plug to keep the signal noises from interfering with the function of various electronics in your GM.
Precise Fitment and Design: OEM plugs are precisely uniform in length, and this is extremely important. Engine tolerances are tighter now than ever, so your spark plugs need to be the precise length. Even it they’re just a few hundredths too long, the plug can interfere with the valves or pistons. Should they been a tiny bit too short, combustion will be incomplete. The “best” way aftermarket manufacturers get around this is by making them too short so they don’t have to invest in the resources needed for precise engineering. Their hope is that you won’t notice the impact and chances in performance.
Why You Should Care
So maybe you’re not looking to squeeze every bit of power and performance out of your engine, and you’re not planning on keeping it long enough to worry about replacing them soon — should you still care? Yes, and the main reason is the effect on fuel economy.
Let’s say, for example, that your aftermarket plugs are a bit too short, don’t have high grade tips, etc., your fuel economy is going to decrease. While this decrease isn’t going to be shocking, it adds up. If you see even a 2% decrease, that adds up to an extra $37.50 each 15,000 miles for a car that averages 24mpg. Over five or so years, that's a couple hundred dollars — way more than OEM plugs…but don’t worry, cheap aftermarket plugs probably won’t last five years anyways.
The bottom line is, spark plugs aren’t where you need to cut corners to save money. Sure, owning a vehicle can get expensive, but downgrading on parts like these isn’t helping to keep money in your wallet. Always use genuine replacement plugs, they pay for themselves in fuel economy alone.