Starting your diesel vehicle involves various parts and a combustion system that relies on those parts.
Since diesel engines use a different type of fuel than standard gasoline, its engine operates a little differently.
When using a diesel engine for the first time, you may wonder when you need to change your spark plugs and how many you’ll need to buy.
Here’s what you need to know about how many spark plugs a diesel has and how to change them.
How Many Spark Plugs Does A Diesel Have?
A diesel engine has zero spark plugs.
It doesn’t use spark plugs because the combustion process is different.
Spark plugs create a literal spark, or small explosion, within the chamber of a gasoline engine.
The engine uses that explosion to ignite the gasoline and start.
Instead of a spark plug, a diesel engine uses a glow plug.
The glow plug is similar to a spark plug in that every cylinder on the diesel engine requires one plug.
In that case, a diesel engine has the same number of glow plugs as it does cylinders.
For example, if you have a six-cylinder engine, then your diesel has six glow plugs.
What Are Spark Plugs?
Spark plugs are a necessary part of the ignition system in gasoline engines.
They help create energy that propels the car forward.
When you turn the key in your car, there’s a quick process that occurs which starts your engine.
Fuel and air mix together in a chamber.
The engine then tells the spark plugs to fire off in a certain order.
The spark plug releases an electric spark which ignites the fuel and creates a small explosion.
This small explosion then forces the piston of the engine down and generates energy for the engine to move the car.
When a spark plug is faulty, then it can no longer create a spark to start the engine.
That’s why it’s important to change your spark plugs every 100,000 miles at the very least.
When one spark plug wears out or experiences damage, then that specific cylinder of the engine won’t fire.
Not only can this damage your engine, but it also means your car either won’t start or won’t start safely.
What Are Glow Plugs?
A glow plug is similar to a spark plug in that it’s used to start the engine.
When you turn the key in a diesel car or truck, before the fuel starts to mix with the air, the air undergoes a compression process first.
It’s moved to a chamber where it compresses.
The piston in the engine then lifts upwards and increases the pressure in the chamber.
The resulting pressure also forces the fuel inside of the chamber and mixes it with compressed air.
This mixing process causes the fuel to evaporate.
The glow plug, meanwhile, heats up.
When the chamber is warm enough and under enough pressure, the fuel in the chamber ignites and the engine starts.
While it may seem as though this process takes a long time, it actually occurs extremely fast.
The glow plug is capable of heating the area extremely fast.
What Do Glow Plugs Do?
Glow plugs have three different functions.
Its primary function is to pre-heat the engine.
As soon as the driver turns the key in the ignition, the glow plugs quickly heat up the cylinder and prepare the ignition process.
The second function is temperature maintenance.
Because glow plugs generate heat, they also need to be able to monitor their own temperature and the temperature of the cylinder.
If they become too hot, for example, then they could start to melt the cylinder since they sit on top of it.
To prevent that, the glow plug moderates its heat and makes the necessary changes to ensure the area stays at an optimal temperature.
The final function that a glow plug has is a post-heating process.
Once the driver turns the engine off, the glow plug maintains its heat.
This enables it to start its pre-heating function quickly.
What Are The Types Of Glow Plugs?
When you are shopping for glow plugs for your diesel engine, you’ll quickly come to realize that there are several different types of plugs.
Choosing the best one for your vehicle comes down to your budget and needs.
Here are the different types of glow plugs and what they’re best used for.
1. Steel Glow Plugs
The cheapest type of glow plug is the steel glow plug.
This is a standard glow plug that most drivers use.
Since they’re made of steel, it can take them a bit longer to heat the engine in cold temperatures.
It isn’t as efficient as the other types of glow plugs, but it will do its job and start your engine.
If you don’t drive often or live in an area with moderate temperatures, then steel glow plugs are likely the best choice for your diesel engine.
2. Ceramic Glow Plugs
The next most-expensive glow plug is a ceramic glow plug.
These types of plugs tend to become hot fast.
The ceramic material used allows them to heat up fast and generate a consistent amount of heat.
They’re able to reach higher temperatures than the other types of glow plugs.
That makes this particular glow plug ideal for those who live in colder climates.
Whether it’s cold year-round or only during the winter season, ceramic glow plugs are a great choice for your diesel.
You’ll have to spend less time attempting to start your vehicle and more time actually driving.
Because they can reach higher temperatures than other plugs, they also make it easier to start your vehicle again after shutting it off.
It maintains the heat longer.
Because they’re able to start your vehicle quickly, ceramic glow plugs have a reputation for being efficient.
That also means your vehicle will run more efficiently.
It takes less fuel to ignite the fuel and operate the vehicle.
Although ceramic glow plugs tend to be on the pricier side, the investment may be worth it for those who live in colder climates.
3. Pressure Sensor Glow Plugs
Often, the most expensive type of glow plug is the pressure sensor glow plug.
This plug doesn’t just start your diesel engine, but it also gives you an accurate reading of the pressure within the cylinder.
This is helpful because it tells you how efficiently your engine is running.
When the pressure starts to go down in a cylinder, then you know you may need to take it in to the repair shop to have it looked at sometime soon.
It also tells the vehicle’s computer about the problem with the pressure.
If your particular vehicle has the smarts to adjust itself, then it can take care of these pressure problems internally.
Besides indicating the pressure inside a cylinder at any time, pressure sensor glow plugs are also great at starting your engine.
They also perform well in colder temperatures although not as well as ceramic glow plugs.
That said, they’re also ideal if you want to keep your eye on your vehicle’s fuel efficiency.
What’s The Difference Between A Hot Glow Plug And A Cold Glow Plug?
All types of glow plugs fall into two categories.
They’re either hot glow plugs or cold glow plugs.
A hot glow plug has a lower percentage of nitrogen in it.
A cold glow plug has a higher percentage of nitrogen in it.
Hot glow plugs tend to be better for operating in colder conditions and improving the performance of the engine.
Cold glow plugs are better for power and torque.
The size of your engine can sometimes determine which category of glow plug you need.
Small engines, for example, benefit the most from hot glow plugs.
Larger engines benefit the most from cold glow plugs.
If you have a turbocharged engine, then you’ll likely need a specific type of glow plug made for that engine.
There are also medium glow plugs that have a nitro-percentage between hot and cold.
Your owner’s manual will tell you the type of glow plug that your engine needs.
How Often Do You Need To Change Glow Plugs?
Maintaining your engine is an important part of being a vehicle owner.
By regularly maintaining your engine, you can make it last for years.
Part of your maintenance routine should be the replacement of your glow plugs.
Since their job is to generate heat, it’s no surprise that they start to deteriorate over time.
The more that you use your vehicle, the faster that they deteriorate.
On average, glow plugs tend to last for 100,000 miles before they lose their efficiency or break.
Most mechanics will suggest inspecting your glow plugs every 12,000 miles since that’s the ideal milestone for auto maintenance anyway.
By 100,000 miles, however, you should replace all of your glow plugs.
Replacing all of them at the same time ensures that every cylinder of your engine continues to operate efficiently.
Recall that even if one glow plug starts to go bad, it can affect the performance of your entire engine.
To make life easier, it’s a good idea to replace all of your spark plugs or glow plugs at the same time.
How To Replace Glow Plugs In Your Diesel Engine
Replacing your glow plugs is a relatively easy process.
Because almost anyone can do it, and because glow plugs are relatively cheap, you can save yourself a lot of money by learning how to change out your glow plugs on your own.
To replace your glow plugs, you’ll need the following tools:
- Torque wrench or socket wrench and ratchet
- Glow plug reamer
- New glow plugs
Follow these steps to safely replace the glow plugs in your diesel engine.
1. Disconnect The Battery Cable
Open the hood of your car and locate the battery.
Because glow plugs rely on the battery to generate heat, you need to disconnect the battery from them for safety purposes.
Failing to do can result in electric shock.
In particular, you’ll need to remove the black negative cable on the battery.
In some cases, you can remove the nut that connects the cable to the battery terminal by hand.
In most cases, however, you’ll need a wrench to loosen the nut before being able to remove the cable from the terminal.
Once you remove the cable and disconnect the battery, you can move on to the next step.
2. Remove The Valve Cover
Some glow plugs sit under a valve cover.
This helps them maintain heat more easily since they’re not exposed to the air.
It also keeps them protected in the event that something hits under your hood.
To remove the valve cover, you need to take your screwdriver and remove the screws holding the cover in place.
This is also a good time to inspect the cover to determine if you need to replace that, too.
3. Remove Glow Plug Wires
Before you can remove the glow plug entirely, you need to remove its wire first.
You’ll find your glow plugs on the head of the cylinder.
Each plug has a wire that connects it to the battery and delivers the 12 volts it needs to generate heat.
The wire uses some form of connection like a bolt or nut to attach to the plug.
Remove the connection to remove the wire from the plug.
In this case, it’s often helpful to use pliers since the bolts, nuts, or terminals can sometimes be stuck tight.
4. Remove The Glow Plug
The hardest part is removing the glow plug because it can sometimes stick to its holder.
You’ll need a socket and ratchet to remove the plug.
Place the ratchet over the plug and rotate it in a counterclockwise movement.
If the plug refuses to move, then you’ll need to use the deep well socket to pry it loose.
After rotating the plug enough, it will be free from the holder, and you can pull it out.
This is an ideal time to inspect the plug.
Since they can sometimes break during the installation process, you’ll want to make sure it doesn’t have any broken pieces.
Cleaning inside of the socket is highly recommended to ensure your car continues to operate efficiently.
5. Install The New Glow Plug
You’ll basically follow the same instructions but in reverse to install a new glow plug.
Carefully place the new plug inside of the socket, and then twist it by hand or with your ratchet in the clockwise direction.
You don’t want to overtighten the plug, however, as this can break it.
6. Reconnect The Cables
Once the plug is in place, you’ll need to attach the wire to it again.
Secure it with your wrench like you did to remove the wire before.
Then place the valve cover back over the plug and tighten the screws down with your screwdriver.
Finally, put the black negative battery cable back in place on the correct battery terminal.
You can then either scan your car’s engine to determine if it’s functioning correctly or start it up.
Diesel engines don’t use spark plugs because their combustion system relies on pressure instead.
To ignite the engine, a diesel engine uses glow plugs.
Similar to spark plugs, a diesel engine uses one glow plug for each cylinder within the engine.
There are various types of glow plugs, and replacing them every 100,000 miles is easy and can ensure your vehicle continues to operate efficiently.