How Many Spark Plugs Does A Diesel Have?

There is actually more than one answer to the question, “How many spark plugs does a diesel have?”. To better understand the answer, let’s examine the differences between gasoline and diesel engines first.

Considering Diesel fuel doesn’t combust by spark, spark plugs are not used with Diesel engines. Therefore, the answer to the spark plug and Diesel question is “zero.” However, there is another answer to the question.

Fuel Consumption in a Diesel Engine?

When you understand how a gas engine burns fuel, you will also understand how a diesel engine differs. Combustion is a chemical reaction requiring heat. The combustion process of diesel engines is carried out by glow plugs, not spark plugs. When the engine is running, the glow plugs can reach temperatures of 1,000°C or more.  

The Second Answer to ‘How Many Spark Plugs Does A Diesel Have?’

Asking “How many spark plugs does a diesel have?” should also take glow plugs into consideration. The two are different, but they both help burn fuel. The answer is one glow plug per cylinder if you look at the similarities. Diesel engines usually have one glow plug per cylinder, so a four-cylinder diesel engine will have four glow plugs.

What Are the Differences Between Gasoline and Diesel Engines?

The primary advantage of diesel engines is their torque. As a result of the combustion process and the differing plugs used in gasoline and diesel engines, diesel engines produce a substantial amount of work-power over horsepower. As a result, most big rigs are diesel-powered. Utility trucks are mostly diesel-driven and pull boats, trailers, and heavy loads.

The movement of weight requires torque. Compared to a diesel vehicle, a gas vehicle will burn five times as much fuel if it performs the same ‘work’ as a diesel. Diesel truck owners never go back to gas for a work truck after they buy a diesel. In everyday life, gasoline is great. However, if a gas owner wants to push and/or pull any kind of load with a vehicle, they usually rent a diesel.

Fuel is used in different ways by different engines. Most internal combustion engines work in the same way, by introducing fuel into the combustion chamber, igniting it, and causing an explosion that propels the piston.

With the moving piston, the crankshaft rotates, which transfers power to the transmission and finally to the wheels. Adding more pistons can increase power. The automotive industry has also spent 130 years figuring out ways to use less fuel while making engines more powerful.

Fuels such as gasoline and diesel burn in combustion chambers in different ways because of their different structures. Fundamentally, gasoline is classified as a flammable liquid, whereas diesel is classified as a combustible liquid.

A spark is all it takes to ignite gas, whereas diesel fuel has a higher boiling point and requires a high-compression combustion chamber to operate effectively as a vehicle fuel.

What Do Diesel Engines Require In Place Of Spark Plugs?

Due to the different ignition points and volatility of conventional gasoline fuel compared to Diesel fuel, diesel engines don’t require spark plugs. Instead, diesel engines use glow plugs.

As a result of the piston design of a diesel engine and the heated chamber produced by the glow plugs, Diesel is converted into a mist, resulting in a more efficient explosion that ignites the combustion chamber.

Diesel Engines Don’t Need Spark Plugs

Using spark plugs, a gas engine ignites the gasoline and creates a combustion stroke. Since diesel engines lack spark plugs, they have compression ignitions and glow plugs that heat the combustion chamber, enabling them to ignite when they are cold. The difference with diesel fuel is that it doesn’t ignite. Thus, a spark plug isn’t necessary when using diesel fuel, because the fuel doesn’t need to be lit. The glow plug only heats the combustion chamber.

The Use of Glow Plugs in Diesel Engines

Due to the piston design and glow plug’s heated chamber, diesel fuel is atomized into a mist. As a result, the mist ignites more efficiently, pushing the piston through its stroke more forcefully. With diesel engines, heat is used instead of an arc, making fuel molecules move quicker, thereby producing higher power efficiency. The larger picture is that both engines require combustion, but with diesel engines, a glow plug instead of a spark plug makes the fuel molecules move more quickly. The compression of a well-tuned gas motor is usually 130 psi. The compression of a well-tuned diesel motor is typically 425 psi.

Can You Start a Diesel Engine Without Glow Plugs?

Due to a lack of compression, your diesel engine won’t start without glow plugs. It is important to understand that glow plugs act as starting aids since they generate enough heat to atomize diesel fuel. Even if your glow plugs are bad, you can still start your diesel engine.

How Often Should You Change Your Glow Plugs?

It is important to check and replace your glow plugs every 12,000 miles during a tune-up to ensure optimal performance. In general, glow plugs last about 100,000 miles.

Typical Diesel Diagnostics & Repairs

Due to the enhanced compression of a diesel engine, every diesel diagnosis must take into account the pressure created. It doesn’t matter whether there is a fuel leak, a coolant leak, blow-by, or almost any service on a diesel, compression affects almost everything. There are times when owners may want to consider a specialty diesel shop for maintenance since many gasoline repair shops fail to properly analyze the differences between diesel and gasoline engines.

Crankcase pressure, for example, is the result of weakened piston rings, which allow compression to blow past the rings and down into the crankcase. Diesel compression increases the chances of the combustion being forced past the rings. By using the proper diesel pistons, rings, and oil, a tighter seal is created, while the friction of a tighter tolerance piston ring is reduced, reducing blow-by and creating an added bond. 

A puffy oil fuel cap can indicate blow-by or that some internal engine repairs are in order. The condition is more noticeable on a diesel engine due to its higher compression. A gas engine can sometimes run for longer under adverse blow-by conditions, but a diesel engine cannot run very well under such conditions, because the higher compression blowing by the rings causes a lack of torque, making it much harder to start.

Maintaining Diesel Engines to Prevent Carbon Buildup

As diesel compression creates more force against moving parts, friction is also added to each revolution, resulting in greater lubricity and improved motor oil flow-through. Diesel engines work harder than gasoline engines because their internal components work harder. Oil and fuel additives help reduce wear and tear, help reduce engine noise on parts that are wearing out, and enhance combustion of diesel fuel in order to counterbalance some of the intensified diesel energy.

When the spark plug is replaced with a glow plug, the mist ignites against more surfaces, resulting in a buildup of carbon. Stiction eliminator additives act as detergents throughout the motor, removing carbon interference and helping restore a more efficient and cleaner burn when build-up reduces the efficiency of ignition.

They don’t change the motor’s performance, but they help counteract the additional stresses of a more efficient motor, thereby extending its life and reducing the total cost of ownership.

The Best Spark Plugs: Our Top Picks for Engine Performance

Since you replace your spark plugs frequently, you need to know which ones are best.

To ensure the best performance of your engine, you need a spark plug that offers the correct temperature, gap, and fit. Once you figure out those basic details, you need to determine which spark plugs are best within those parameters. Here are our recommendations:

NGK Iridium IX Spark Plug

We chose the NKK 6619 Iridium IX Spark Plugs for their exceptional performance, fuel efficiency, durability, and dependability in our spark plug comparison. In comparison to copper and platinum spark plugs, these high-quality iridium spark plugs provide a longer lifespan.

With its ultra-fine electrode wire, this spark plug delivers superior fuel efficiency as well as silky-smooth engine idle and response. Thanks to the perfect air-fuel mixture generated by these iridium spark plugs, you’ll also get a boost in power and torque. Furthermore, it is highly durable, thanks to a long insulator nose to prevent fouling, as well as metal plating to resist corrosion and seizing.

ACDelco 1 Professional RAPIDFIRE Spark Plug

This is a spark plug that is versatile with many vehicles. In addition to providing excellent heat transfer and increased durability, this spark plug is made with 100 percent pure copper core. For improved plug-to-boot sealing and preventing leakage, ribless insulators are used. The suppressor reduces radio frequency interference and regulates spark energy for longer electrode life with a two-piece glass and brass seal. A platinum center electrode enables superior spark characteristics and reduces vehicle ignition system voltage requirements, protecting against high combustion pressures.

Be sure to check your owner’s manual before ordering to ensure that these are the right spark plug for your vehicle. Since these are not iridium spark plugs, they won’t work in every vehicle.

Denso Platinum TT Spark Plug

Look no further than Denso 4504 PK20TT Platinum Spark Plugs if you’re looking for a solid all-around spark plug that won’t break the bank. These discount platinum plugs are highly efficient, durable, and affordable.

In addition to a platinum electrode tip and platinum disc construction, these spark plugs provide a reliable spark that ensures the smooth combustion of air-fuel mixtures. In addition to increasing thermal conductivity for maximum longevity, purified alumina powder serves as an insulator for improved engine dependability, fuel efficiency, and performance.

NGK V-Power Spark Plug

Compared to your standard spark plug, this plug features a V-Power center copper or platinum electrode that provides performance, improved ignitability, improved fuel economy, and lower emissions. This spark plug has anti-seizing properties and is completely corrosion-resistant. Because of its unique cut in the middle, the spark is directed to the edge of the electrode, resulting in faster, more efficient sparking. As a result of the corrugated ribs, flashover is prevented, while the pure alumina silicate ceramic insulator increases strength and heat transfer. A triple seal prevents leakage, and this plug is highly durable to protect against electrical and chemical wear.

You should inspect your product upon delivery to make sure there are no manufacturing issues or defects before installing it in your vehicle. Some customers reported their spark plug coils to be defective.

Bosch Copper Super Plus Spark Plug

For optimum performance, reliability, and heat transfer, these spark plugs feature nickel-chromium ground electrodes with heavy-duty yttrium-enhanced copper core centers.

No gapping is required with these plugs, and their ribbed insulator prevents flashover. The nickel-plated shell provides anti-seize and corrosion protection. In some vehicles, the plugs can increase mileage and may boost performance by a noticeable amount. They resolve misfires in some vehicles and can increase mileage.

Bosch Copper with Nickel Original Spark Plug

Iridium firing pins are welded using a laser, and the copper core is designed to reduce fouling. Its long lifespan and durability make this OE replacement plug a great choice. There is no gapping required, and the plug is corrosion-resistant due to its nickel-plated shell.

The best thing about these plugs is that they last for a long time, which is important if you have an engine where it is difficult to access the plugs. They are extremely reliable, and you do not need a special gap tool to install them. Even if you don’t notice a difference in mileage, you may see an improvement in performance.

Champion Copper Plus Spark Plug

There are four packs available of the Champion Copper Plus C33-438 Spark Plug, which features a nickel alloy center and ground electrode, providing reliability and durability. An increased level of conductivity and heat control is provided by the copper in the center electrode of this spark plug. It is a great choice for all types of automotive engines, especially older models. Besides vehicles, these spark plugs can also be used for lawn and garden equipment and smaller engines. Be sure to check your vehicle’s owner’s manual or your equipment’s instruction manual before using these plugs as a replacement.

Make sure that you consult your manual or contact your vehicle manufacturer before attempting to replace spark plugs in newer vehicles or engines.


In choosing spark plugs, it’s important to be aware that new ones with different materials for the center electrode can reduce engine corrosion. From our selection of recommended spark plugs for replacing worn plugs, we hope our review of the best spark plugs has been helpful and you were able to find the one that is right for you.