How Many Spark Plugs Does A Diesel Have? (Explained)

If you’ve been thinking about doing a tune-up to your truck or car, you might wonder how many spark plugs does a diesel engine have? Many enthusiasts and at-home mechanics have struggled to answer this question.

This guide will help you answer all your questions about spark plugs. This guide will help you to understand how the system works and what is found within the diesel engine. 

Do Diesel engines have spark plugs?

The diesel engine does not have spark plugs. Glow plugs are used to power diesel engines. In most cases, there is only one glow plug per cylinder. Your 8-cylinder diesel engine will have eight glowplugs with a standard setup.

Diesel and gas engines work in different ways. A heating device is required for the diesel engine. This is why glow plugs have been developed. Although the spark plug and glow plug look similar, they serve a different purpose.

What are Spark Plugs?

Every gasoline-powered engine has a sparkplug. One spark plug is usually found in every cylinder of a gas engine. If you have a six-cylinder engine you will likely need six spark plugs. One for each cylinder.

This spark plug is ignited in an order by the engine. A small explosion occurs inside the engine to ignite the mixture of air and fuel. 

The piston in your engine is compressed when the explosion happens, creating energy which propels your car forward. However, the diesel engine doesn’t require ignition to operate. The engine requires heat and pressurization, which are exactly what glow plugs offer. 

RELATED: 6 Symptoms of Bad Spark Plugs (& Replacement Cost)

What is a glow plug?

It acts as a heating element. It looks like a spark plug, but it’s not igniting fuel or air in the pistons. 

Even in warm climates, the diesel engine may run on its own without glow plugs. The cylinders have an electrical heating element that helps maintain a steady start when the temperature drops. 

RELATED: 5 Symptoms of a Bad Diesel Glow Plug (& Replacement Cost) 

What number of glow plugs does your diesel engine have?

You will be surprised to know that the number of glow plugs in your diesel engine is almost equal to how many you'd find in a gasoline engine. Most likely, there is one glow plug in each cylinder of your diesel engine.

Six glow plugs are required for a diesel 6-cylinder engine. Eight glow plugs are common for the diesel 8-cylinder. However, exceptions can be made to this rule. 

There are stages when glow plugs may be needed

1. Pre-Ignition

The glow plugs heat up the cylinders before ignition occurs. After the ignition switch is turned ON, the glowplugs go to work.

Some diesel drivers experience higher performance when they leave the ignition ON until the engine is started. In older vehicles, the heating process can take a little longer, so it’s best to allow for some time. 

2. Ingnition

The glow plugs are also helpful when you crank the engine. However, glow plugs aren’t used to create a spark that ignites the air and fuel mixture.

Instead, glowplugs in this period merely keep the temperature up to promote better combustion. When the temperature is just right, combustion will occur quicker and more efficiently.

3. Post-Ignition

For a time, after turning the engine on, the glowplugs keep the combustion chamber warm. The temperature of the combustion chamber should be maintained at a high level to ensure that efficient combustion takes place.

In addition, the combustion chamber heats faster and produces less noise. Everything runs smoothly thanks to the glow plugs. 

Different types of glow plugs

1. Pressure Sensor Glow Plugs

An integrated pressure sensor makes this glow plug possible. The sensor provides information about cylinder pressures that is sent to the engine control module (ECU) which improves engine efficiency.

PSG Plugs work well in colder weather to start the car. These plugs can improve fuel economy as well as reduce emissions. 

2. Ceramic Glow Plugs

Ceramic glow plugs heat faster. The ceramic glow plugs heat up much faster than the other types and reach ideal temperatures sooner than any other plug.

You will need this plug if you reside in a colder area. You don't have to wait for your plugs warm up. Instead, start the engine right away and burn fuel at the optimal temperature. 

3. Glow plugs made of steel

One of the most affordable options is the steel glow plug. It’s designed to save you money, but it still works well enough to be considered reliable.

Steel glow plugs are available in two and three stage versions. The three-stage system is more popular today than the two-stage systems that were used in older engines. You can expect a longer start time with the steel plug but it should still work in cold weather. 

Diesel Glow Plug Replacement Cost

The cost to replace glow plugs on a diesel engine could be $200-$300. Parts could cost $75-$125, and labor might be $125-$175 

In cold climates, the engine may take longer to start if the glowplugs are failing. The glow plugs that are attached to the block heater will cause less problems. There may be performance problems until the engine has reached normal operating temperatures. 

However, it’s possible to drive with bad glow plugs. Because the glow plugs aren’t needed for the normal operation of the running engine, there should be no major issues continuing to use your vehicle after the plugs fail. You will notice most problems when the engine is started in cold temperatures.