Last Updated: 04.08.2021

Without the spark plug, a gas engine is useless; it’s the spark plug that enables the engine to function. Of the various important components in an internal combustion gas engine, the spark plug is possibly one that you just can’t do away with. And why’s that? That is because the spark plug takes care of the combustion in a gas engine. That means in its absence, there won’t be a power stroke. And that in turn means your vehicle will not be able to move at all.

To understand why the spark plug matters this much, we must take a look at the basic functioning of the engine. We’re talking about a conventional (Otto cycle) gas engine that has multiple cylinders and thus multiple spark plugs. In a four-stroke engine, each cycle (denoted by one complete rotation of the crankshaft) has four strokes. These are intake, compression, combustion, and exhaust. Now the third step, which is combustion in this case, is handled by the spark plug. This holds true for gas engines, whereas in diesel engines the process is slightly different and diesel engines don’t use spark plugs. In the case of diesel engines that happens because of the compression itself — it’s done to a higher degree. But when it comes to gas engines, the combustion requires an external source. And that’s the spark plug. This process is achieved by sending a high voltage between two of its electrodes. It ignites the mixture, which forces the piston to move down. That in turn sets the entire engine cycle in motion. Depending on the type of engine, the number of spark plugs per cylinder varies. In most of the modern engines, that’s generally one or two per cylinder.

Why is a Spark Plug Important in an Engine?

5.3 Silverado with Spark Plugs.

Types of Spark Plugs

Generally there are three types of spark plugs, depending on the electrode tip they have. The most common one is the nickel alloy tip. But if you’re after better performance and longer life, the platinum and iridium choices are hard to ignore. The price difference between individual plugs isn’t much, so if you’re considering a new set of plugs, you must look at all the choices. Choosing a plug that lasts longer will also benefit the cars in which accessing the spark plugs is a task in itself. So the longer it runs, less is the headache of changing the plugs. Depending on the type of engine, there are hot plugs and the high-performance cold plugs. The difference between these is the amount of insulation.

Spark Plug Anatomy

That brings us to another point: the spark plug’s construction. We’re sure most of you have seen one. It has a central electrode and a ground electrode separated by a manufacturer-specified gap. These two are responsible for the travel of electricity and thus creating a spark. The central electrode is surrounded by an insulator to ensure that the spark takes place only at the tip and not anywhere else. And depending on the type of plug, there’s a varying amount of ceramic insert next to the electrode. It helps dissipate heat and thus burn off deposits on the electrode. On the other side of the plug, there’s a connector from which the plug draws its electricity. Every spark plug has a predefined socket size. This makes it easier for you to find the one that fits your vehicle. And not just responsible for combustion, the plug also helps in transferring heat from within the chamber to the cooling system.

Changing your Spark Plugs

So how do you make out if the plug is on its way out? It’s easy, actually. The vehicle starts to misfire — you can hear it do so, and if not that, then there’s the very clear drop in performance. If a plug doesn’t work, it basically means your car/truck is running on fewer cylinders. And if you’re used to driving this particular vehicle, it won’t take too long before you decipher that something’s wrong. A decrease in fuel economy can also suggest that the fuel isn’t being burnt effectively — and a faulty plug is the reason why. One of the most common ways to find out if it’s time to change the spark plugs is by keeping a check on the odometer and sticking close to the manufacturer-specified intervals.

If you’re doing it yourself, you must not stray too away from the manufacturer guidelines. Some vehicles aren’t very easy to work on, so keep in mind that for such cases, you’ll need to factor in the cost of labour along with the plugs. It’s recommended that the plugs should be changed individually — you find one plug, replace it, and connect the wire and move on to the next. The removal and installation of new ones must be done only once the vehicle is turned off, cooled down, and the battery is disconnected as well. 

Does a wrong spark plug affect the engine? Yes, it can. And a used spark plug can give you some information about how the engine is. It should have no oil on it, some deposits are fine (because you can’t expect the plug to be clean unless you changed them very recently) but keep an eye on signs that might suggest any malfunction/incompatibility to ensure the engine stays healthy — and for long.


Another common question that owners and enthusiasts have is whether a high-performance plug changes the way their vehicle drives. There will be some performance enhancements, especially if the plug produces sparks easier than in the conventional systems. But these won’t necessarily be tangible. If you’ve upgraded your engine, it might make sense to get the most of the upgrades, so a high-performance plug doesn’t sound like a bad idea. A solid reason to stick to more premium plugs is the longevity, though. They last longer than standard plugs, and if that means a more hassle-free ownership at about $2 per plug, that’s not too much, is it?