Do diesel engines have spark plugs? – Find out the truth!

Do diesel engines have spark plugs_

We get a number of questions about diesel engines and one of the most repeated ones these days is “do diesel engines have spark plugs?”

You are finally going to have the answer!

Do diesel engines have spark plugs?

The answer is no. Diesel engines don’t have spark plugs. Petrol-powered engines do. Spark plugs work to start the vehicle and keep it going. Diesel engines don’t need that.

Why do diesel engines not have spark plugs?

This is because they work on compression ignition. And compression ignition has no use of spark plugs. Instead, they have something called glow plugs. 

Why do diesel engines work without spark plugs?

Good question! There are several reasons why, despite being similar to petrol engines, diesel engines don’t have spark plugs. The main reasons are as follows:

  • Diesel engines are less volatile. 
  • The self-ignition temperature is low
  • Atmospheric air gets compressed and creates high pressure. This increases the temperature. Thus, there’s no need for a spark plug.

The presence of a spark plug in a diesel engine is redundant because it serves no purpose.

What are glow plugs?

Glow plugs come fitted in the compression ignition. They can be explained as small heaters that work to warm compressed air. When the air warms up, ignition is easy, especially when the engine is cold. It comes to life immediately! 

How does a glow plug work?

Glow plugs are useful only during the ignition process. Spark plugs need to function continuously right from the start to when the vehicle comes to a stop.

Glow plugs electrify the heating element and emit light (which is why they are called glow plugs). The intake air gets compressed before the fuel reaches the tip of the glow plug. This fuel then mixes with the now compressed air and combusts. That’s how even a cold engine can start up quickly.


We shall now answer a few more related FAQs.

1) Are my glow plugs not functioning properly?

There’s an easy way to find out. Here are a few signs you should look out for: 

  • Engine not starting easily
  • Engine emits black smoke upon startup. Black smoke is an indicator of unburned fuel. This happens when the combustion doesn’t take place properly.
  • Engine emits white smoke
  • Engine misfire
  • Bad fuel efficiency

If you see any of these signs, there’s a problem in the glow plug and you should replace it immediately.

2) How many glow plugs do diesel engines have?

Diesel engines have 10 glow plugs. Each cylinder needs a glow plug. Since there are 10 cylinders, there are 10 glow plugs.

3) How much will it cost to replace a glow plug?

You can expect to pay between $25 and $50 for a new glow plug. The exact price will depend on the brand you go for.

We hope we have answered all your questions about spark plugs and glow plugs. If we missed any, please comment and we will be happy to update our list. We are looking forward to hearing from you.

Francis Ceron

About Francis Ceron

Did you know the major cause of car failures are due to spark plugs. At sparklplugs guru you wil find all the necessary reviews, guides and facts to improve the performance of your vehicle and have a smooth functioning.

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