4 Signs It’s Time for New Spark Plugs – Jalopnik

Spark plugs play a key role in keeping your engine running because it’s that small electric shock that ignites the fuel-air mixture in an engine’s cylinders. And that small spark must be delivered in large numbers, because the spark plugs must ignite once every two revolutions of the crankshaft. That means that when an engine is running at 3,000 rpm, the spark plugs fire 1,500 times per minute. They must also withstand extreme temperatures and function best when their center electrodes reach a temperature of 932 to 1742 degrees Fahrenheit.

Although spark plugs are designed for a long life, you will eventually need to replace them. In fact, you should replace your spark plugs every 50,000 to 100,000 miles. There are many reasons why oil can appear on your spark plugs, all of which can lead to premature replacement. Carbon buildup and overheating can cause the same problem. Problems with the gap between the center electrode and the ground electrode – where the spark originates – can also lead to damage. The good news is that you generally don’t need to adjust the gap on preset spark plugs.

Bad spark plugs affect the combustion process, causing your engine to generate less power. You may notice deteriorating performance, deteriorating efficiency, and even some unexpected noises due to improper fuel/air ignition. If you’re not sure if your spark plugs need to be replaced, here are four signs to look out for.

Although spark plugs are what get your car running in the first place, they have to get their electricity from somewhere. That’s a key role of the battery in typical cars today. Historically, electricity was supplied by a magneto, a device that can generate electricity by moving a magnet through a special arrangement of metal wire. Early engines could be started with an electric starter, but they could also be started by hand, which would spin the magneto and send electricity to the antique spark plugs.

Bosch invented modern high-voltage spark plugs in 1902, but as we discovered when we asked our readers about starting dead cars, magnetic ignition lasted for many years. One commenter reported having to hand-crank his 1960 MGA coupe.

Anyway, the point is that a bad spark plug may not create enough spark to completely burn all the fuel and air in a cylinder. When that happens, the burning materials don’t expand as quickly or as much as with a full spark – and may not provide enough power to actually get the engine going on its own. At least not on the first try, and possibly not at all.

Sometimes an engine with bad spark plugs will tell you there is a problem as long as you speak the language. For example, let’s say you hear a metallic knocking sound under your hood. That could be your engine complaining of detonation, which can also happen if there isn’t enough spark for complete combustion. When that happens, the unburned fuel and air not ignited by the weak spark can ignite on their own, with combustion occurring just before the piston is supposed to push exhaust gas out of the cylinder.

The collision between the two forces causes the knocking sound. It can also wreak havoc on your engine, damaging and destroying pistons, cylinder walls, connecting rods and more. This is also a good place to remind people that what we’re talking about here, detonation, is not the same as pre-ignition. That term refers to the early combustion of fuel and air before the spark plug ignites. Pre-ignition can also be the result of bad spark plugs, and is much more destructive than detonation because an entire charge of fuel/air is burned, rather than just the leftover material from a spark.

If your spark plugs aren’t working properly, any fuel not burned during the combustion stroke is wasted gas, pure and simple. Consider a car that gets 30 mpg, which means it can go 30 miles on one gallon of gas. But it has bad spark plugs that prevent 10% of each gallon from igniting at the right time (during the combustion stroke). In that case, if you put a gallon of gas in the tank, only 90% of it will help motivate the vehicle. If you do the math, you’ll see that the car only gets 27 mpg. You might as well have just poured that unused gas down the drain.

This is of course harmful to the environment, but the same applies to bad plugs. The fuel they don’t burn ends up in your exhaust system. There it can put extra pressure on the catalytic converter, which has to work harder to deal with the extra emissions, and what isn’t captured by the cat can go straight into the air. But that may not be the problem. It used to be that automakers want the EPA to let them build dirty cars.

Performance is kind of the other side of the coin here. On the one hand, defective spark plugs can mean that you have to use more gas to travel the same distance as your car would with new spark plugs. But for the same reason, it also results in you having to use more gas to achieve the same acceleration speed you are used to.

Some people think you can take that logic to its extreme and increase the base level of a car’s engine performance by upgrading the plugs. However, we don’t believe those so-called performance spark plugs add much horsepower unless they replace old spark plugs that are already actively sapping your engine’s current power.

Using materials like iridium or platinum for the tip can produce a strong, more consistent spark that boosts power and efficiency, but their real benefit lies in the ability of these materials to withstand the enormous pressures and temperatures within an engine’s cylinders. Above the above electrode temperature, the plug itself can be heated to 5432 degrees during combustion and subjected to a pressure of about 735 pounds per square inch.