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Do Semi Trucks Have Spark Plugs? (10 Facts For Beginners)

In this article, we will explore the different ways your truck is powered, and how the fuel is converted to energy.

The maintenance and upkeep of your truck are paramount, regardless of the fuel it uses, but be sure to note the distinctions.

Here’s a quick answer to whether Semi Trucks have Spark Plugs:

Semi trucks with gasoline engines such as the Cummins L9N and B6.7N have spark plugs whilst semi trucks with diesel engines use glow plugs. In gasoline engines, sparks from spark plugs are used to ignite the fuel, since the heat generated from the compression stroke is insufficient for ignition.

What are Spark Plugs and do Semi Trucks have them?

A spark plug is the part of an automobile that ignites the fuel to power the vehicle.

This is necessary for a car, but diesel powered semi trucks do not have spark plugs and rather have something called a glow plug which heats the fuel powering the truck. 

Semi trucks are diesel engines, which differ in several ways from the gas-powered engine of the average automobile.

Gas-powered cars require the ignition to start and power the car. In other words, the gas must be ignited by a spark in order to fuel the car and get it moving. 

Semi trucks are warmed up by the glow plug and the compression ignition which does not create a spark. Rather, these glow plugs create warmth which enables the fuel to power the truck. 

How do Spark Plugs in a Semi Truck work?

The engine in a semi truck is powered by the compression-ignition combined with the pistons of the vehicle.

These work in combination to turn the diesel fuel into a sort of mist which is then channeled through the engine. 

The glow plug works by heating the fuel which causes the molecules to move in a rapid motion.

This actually creates more energy than the traditional gasoline car with the spark plug. This means the truck can travel and pull more weight with greater efficiency than a car.  

Do Semi Trucks with Diesel Engines have Spark Plugs?

Diesel engines do not use spark plugs, because the power produced by the warming of the gas rather than the spark ignition is more efficient.

The diesel engine produces over 140,000 BTUs of energy, compared to the 125,000 from gasoline. 

It is very rare for semi trucks or large work vehicles to be powered by gasoline. Although gasoline is typically cleaner and sufficient for powering an automobile, for large trucks the extra strength is essential.  

Diesel also extends the life of the truck so that it is capable of driving long distances without suffering too much wear or breakdown of the engine. 

How many Spark Plugs does a V8 diesel have?

The short and sweet answer is, diesel engines do not have spark plugs, so a V8 diesel doesn’t either!

However, they do have glow plugs, and a V8 diesel can have up to 10 glow plugs that work to heat the fuel. Typically, there is one glow plug per cylinder. 

Glow plugs are vital, and if one breaks it can mean your engine won’t start or it will have difficulties starting.

Without the glow plug, the piston cannot move any warm air down into the fuel and thus heat it up for power. 

Do all Semi Trucks with Gasoline Engines have Spark Plugs?

It is very rare for a semi truck to have a gasoline engine. In fact, in many instances, they aren’t permitted to use gasoline because they are too inefficient when burning gasoline.

However, there are some hybrid models which utilize both diesel and gasoline. 

On the rare occasion that a semi truck is designed for both gasoline and diesel, then they would require to have spark plugs.

This is because gasoline engines require a spark to ignite the fuel in order to power the engine. 

So, the answer is, although extremely rare, in the instances where gasoline is used, spark plugs are a must. 

Which Semi Trucks have Spark Plugs?

As stated above, it is rare for semi trucks to have gasoline engines and diesel engines due to fuel efficiency.

However, some semi trucks do have gasoline and diesel to help alleviate emissions. Freighliner’s model will be discussed further below to illustrate this.

The Freightliner 114SD utilizes both the Cummins gasoline engine, and the Detroit diesel engine. The engine should be selected based upon the types of driving you do, and the weight of your loads. 

The weight may require the strength of the diesel engine, but gasoline can save money and emissions if selected for the right reasons.

You can read more about this here.

How Many Spark Plugs does a Semi Truck Have?

The number of spark plugs in any automobile is usually the same as the number of cylinders.

In most semi trucks the number of cylinders is around 6, and this means the number of spark plugs is around 6 as well.

Spark plugs are located at the top of the cylinder and create the spark. 

Cummins is the most popular gasoline engine used in semi trucks.

There are 2 models which are the most common which are: B7.7N and the L9N lines which include the popular ISX12N. These engines both have 6 cylinders and 6 spark plugs. 

You can find out more about the different engines here.

Can you drive your Semi Truck without a Spark Plug?

You can drive a semi truck if there are broken spark plugs, but you want to be careful.

Broken spark plugs can lead to misfires, trouble starting the engine, among other issues. The other spark plugs can compensate for the broken one, but should be repaired.  

If there is only one cylinder, and the only spark plug has broken, there will be nothing to start the engine and the truck will not start. This is because it would be the only one that is there to start the truck.

However, this is more of an issue for small cars which have only a few cylinders.

Most trucks have several cylinders and several spark plugs. So you should be able to make it, but get it fixed right away. 

How do you know if your Spark Plugs are Bad?

The best indicator of broken spark plugs is if your vehicle won’t start. If enough of your spark plugs are broken, you will likely be unable to start your vehicle.

Other signs are rough idling and difficult starts with a lot of “bumps” and chugging sounds. 

If you idle your vehicle and find that it is shaking a lot, this is a sign of irregularities in your engine. The spark plugs are important in powering your vehicle and if they break your truck’s functions will break down.

Other signs are issues accelerating and jerking as you stop your vehicle. Although these signs may differ a little from cars to trucks, the basic signs remain the same. 

How Frequently should you replace your Spark Plugs on your Semi Truck?

Spark plugs should be replaced every 30,000-90,000 miles for a semi truck. This should be adjusted based on the type of driving you do, and what the manual directs.

Additionally, keep an eye out for tell-tell signs that your spark plugs are suffering. 

Every truck has different specifications, but the 2 Cummins engines we have discussed previously have distinctive schedules.

The L9N engine instructs users to change the spark plugs every 45,000 miles, and after about 12 months. 

Likewise, the B6.7N has more horsepower and instructs drivers to be a bit more cautious. These should be changed every 25,000 miles and about every 9 months.

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