The question, “how many spark plugs does a diesel truck have?” may seem so easy. Well, that is not the case. There are different answers to suit different situations. The best way to approach this question is to understand the difference between diesel and gasoline engines.
For instance, a six-cylinder gas-fueled vehicle has six spark plugs while diesel trucks don’t have any spark plugs. Instead of using a spark plug to ignite the fuel, diesel engines depend on compression to increase the combustion chamber’s air temperature and burn the diesel fuel immediately upon starting.
Difference Between Diesel and Gas Engines
The key factor to understand the differences between diesel and gas engines is how these engines use different types of fuels. In general, internal combustion engines work similarly. When you put fuel into the combustion chamber of an engine, the fuel combust or ignite and then triggers the piston to move.
As the piston moves, the crankshaft starts to rotate as well. And so the power is sent to the transmission, making the drive wheels go around. To add more power, you can add more pistons. Over the years, automotive engineers continue to discover solutions to make engines more powerful with less fuel used.
The difference in the structure of diesel and gas fuel makes each engine function differently in terms of burning the fuel inside the combustion chamber. Diesel is a combustible liquid while gas is a flammable fluid. Meaning, a spark is all it takes to combust gasoline.
However, the higher boiling point of thicker diesel needs more compression in the combustion chamber so that the fuel source will become effective.
Gas can be a dangerous fluid under certain circumstances such as spilled fuel from car accidents with perforated gas tanks.
An uncontrolled flame or spark can quickly ignite gas while the smoke, not the fluid itself, easily catches on fire. A lit match can be extinguished by diesel, but this is not advisable to anyone. Remember, diesel is a dangerous substance and should be handled with safety precautions, especially when storing this fuel.
Again, diesel and gas engines are different when it comes to how they use their fuel sources. In gas engines, fuel is introduced into the chamber while the spark plugs ignite the fuel. Then again, diesel fuel doesn’t work with gas engines as spark doesn’t help combust the fuel. If you put diesel in your gas engine, expect a repair.
How Do Diesel Engines Run Without Spark Plugs
Diesel engine cars don’t have spark plugs to start with. If you compare gasoline to diesel fuel, gas is more volatile than diesel. It doesn’t take much before it catches fire, therefore spark plugs are used for gas engines.
To get an idea of how diesel engines run without spark plugs, watch this video:
Spark plugs supply an electric arc or spark, that’s how it got its name. The spark ignites the gas fuel in the chamber. As a result, it causes the piston to move, making the engine work.
On the other hand, diesel isn’t that simple to ignite. Spark plugs are not enough to burn the fuel and start your engine. Atomizing the fuel such as spraying it straight from the bottle can build an open flame which ignites and creates a fireball. This is what usually happens in diesel engines.
Glow plugs are used to heat diesel and make the engine easier to start. During warm weather, diesel flows easily so it’s easier to ignite with heated air in the chamber.
Even if the glow plug is faulty, you can still start your diesel engine. However, the climate has to be warm for the glow plugs to easily work. Now if you’re in a cold area and you need to start your diesel engine, you can do so even without using glow plugs. The thing is, it will surely take more time and effort to run the engine properly.
Unlike gasoline engines, only air is injected into the combustion chamber while the piston compresses it. Compressed air then increases temperature, triggering the diesel fuel injector to spray the fluid into the heated air.
The resulting mixture combusts as the pistons move up, then go out of the combustion chamber. This is how diesel engines fundamentally work without spark plugs.
Why Diesel Engines Don’t Have Spark Plugs
Diesel engines don’t have spark plugs. The ones you see that seem like spark plugs are called glow plugs. These types of plugs are designed to heat diesel fuel before introducing it into the chamber. This makes ignition easier and faster for the fuel.
While spark plugs are an essential part of the combustion activity in gas engines, glow plugs are used to start the diesel engine.
However, the weather is an important factor in starting a diesel engine with glow plugs. Cold weather will make it hard for the air inside the chamber to get hot and ignite the fuel.
In some cases, a misfire can cause smoke belching from the exhaust of vehicles. At high temperatures, glow plugs can malfunction and may not start the engine properly.
Essentially, glow plugs are heating coils that are sheathed in metal tubes. The tubes are then filled with electrically insulating ceramic powder. Sealed on each end, the battery of the car sends electricity through these glow plugs. In a few seconds, it can reach up to 1000 degrees Celsius.
Glow plugs made of ceramic are a bit more expensive, but they are more efficient compared to metal glow plugs. The ceramic plugs allow them to easily heat the diesel fuel much faster. In addition, they are longer lasting than metal-encased glow plugs.
Glow plugs don’t just heat diesel, they also heat the engine for proper functioning right after starting the diesel engine. To learn more about glow plugs and how they function, check out the following processes:
- During the pre-heating process, the glow plugs easily heat the diesel to start the engine faster. There will be a red hot glow in the plug while the injector blows atomized fuel over the glow plugs. Then, the plugs are heated up substantially to ignite the pressurized air in the combustion chamber easily.
- When it comes to temperature maintenance, the glow plugs need to keep an ideal temperature to make sure the fuel will ignite easily in the chamber. Also, they stay energized for multiple engine cycles so that it’s certain to start properly.
- For the post-heating process, the glow plugs stay energized for several minutes after starting the engine to keep the combustion. Then after that, the plugs continue to heat the diesel fuel for a few minutes to ensure the engine doesn’t die before it recovers from normal running temperature.
If you want to know how to spot faulty glow plugs, there are a few helpful tips to consider. For instance, you may notice hard starting whenever you try to ignite the engine. Unlike older diesel engine vehicles, glow plugs in modern cars may not perform the same way as starting even if the plugs aren’t working.
Perhaps, your car is no longer starting with only one twist of your key. If it’s taking longer to start the engine, the glow plugs might be the culprit. Problematic glow plugs become inaccurate in heating the diesel fuel and air in the chamber to aid the combustion process.
Moreover, defective glow plugs don’t get hot enough to heat the fuel before introducing it into the chamber. As a result, you experience hard starting, particularly in warmer weather.
Another problem that may arise with a faulty glow plug is engine misfire. In this situation, the glow plugs couldn’t heat the fuel which leads to an engine misfire. This means that the glow plugs won’t ignite the diesel fuel introduced into the combustion chamber.
In addition, the chamber may get overfilled with fuel which can cause weak power output. Engine misfires often lead to some common issues including clogged fuel injectors and engine knocking.
In case the engine doesn’t start at all due to cold weather, there might be some malfunctioning glow plugs in the starter motor. Faulty glow plugs can be identified when you suddenly hear the diesel engine turn over even without starting it.
Now if the battery is at fault, you will hear clicking sounds which means there’s a lack of power in the starter engine. It’s important to consult a professional mechanic to address these issues if you’re not sure you can fix this.
Frequently Asked Questions
How Many Spark Plugs Does a Diesel Truck Have?
Since diesel fuel does not combust using spark, diesel engines do not have spark plugs. So the answer is, a diesel truck has zero spark plugs. However, there’s another approach to this question which is by comparing glow plugs to spark plugs.
Glow plugs and spark plugs are different, but they function the same way when it comes to burning fuel. In terms of their similarities, the answer to the question is one per cylinder. Per engine cylinder, a diesel engine has one glow plug. Therefore, there are six glow plugs for a six-cylinder diesel engine.
How Do Diesel Engines Burn Fuel?
When it comes to gas engines burning fuel, it’s important to understand the differences between diesel engines. Combustion requires heat as well as other elements.
Therefore, diesel engines often use a glow plug instead of a spark plug to heat and ignite the fuel during the combustion process. Glow plugs can reach a temperature of up to 1,000 degrees Celsius.
When Should You Replace Your Glow Plugs?
Cars with four-cylinder diesel engines can be difficult to start even with just one problematic glow plug. If there are two problematic glow plugs, then it will be more difficult to start the engine. A cold morning and three damaged glow plugs can make it impossible to start your car.
It’s important to immediately replace faulty glow plugs to prevent more serious and expensive mechanical problems in the future.
Ideally, glow plugs should be replaced before they reach the end of their lifespan. Since they are only used when starting the diesel engine, they deteriorate gradually.
With a long lifespan, glow plugs are approximately equal to 100,000 miles. Compared to spark plugs, replacing glow plugs is more affordable and easier. Even if you need to replace the entire set of glow plugs, they are not expensive at all.
What is the Role of Diesel Engines in Trucks?
With a valuable role in the car market, diesel engines remain powerful despite the uproar of gas engines in the automotive industry. Diesel engines produce more torque than gas engines. Therefore, it is much preferred in trucks that deal with heavier loads.
Torque is a low-end engine grunt that’s ideal in vehicles that carry heavy loads such as passenger SUVs and cargo trucks. Unlike vehicles powered by gas engines, trucks with diesel engines perform better, undergo less engine stress, and use less fuel.
Why Spark Plugs Are Unnecessary in Diesel Engines?
The main reason spark plugs are not important in diesel engines is because they aren’t needed in inducing the combustion of the fuel.
In a diesel engine, the cylinder sucks the air and then compresses it using high pressure to increase the temperature until it ignites the diesel. Once ignited, the diesel expands while getting the power stroke.
The Bottom Line
There is no spark plug in a diesel truck, this is the key takeaway from this article. Diesel compresses the air inside the cylinder and uses heat to ignite the atomized fuel. However, diesel engines use glow plugs to start the engine by heating the atomized fuel inside the cylinder.
The glow plugs are energized when you start the engine, which is the main difference compared to spark plugs. In general, diesel is more essential to commercial trucks, buses, and other larger vehicles. The more you know about how diesel engines work, the better you can handle your auto needs in the long run.