What Is a Glow Plug?

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  • Written By: Mary Lougee
  • Edited By: Lucy Oppenheimer
  • Last Modified Date: 14 February 2015
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A glow plug, sometimes spelled as one word — glowplug — is a car part that looks a lot like a spark plug. Used in vehicles that don't require spark plugs, namely those that operate on diesel engines require these devices to have enough heat to start up. Glow plugs are also used to start remote control cars, trucks, boats and airplanes.

Identifying a glow plug is pretty simple. It has a pencil-like shape and is made from a high heat-resistant metal, like platinum or iridium. On it's end is a heating element with a temperature sensor. When the plug is "on," it warms the engine, much like the heating elements warm up the space inside a toaster. Once the engine block is sufficiently warm, the vehicle can be started. This process is the same on both diesel vehicles and remote control cars and only takes approximately two to three seconds.

Older model vehicles with diesel glow plugs were started by turning the key to the on position. This would illuminate an indicator on the dashboard showing that the glow plug was lit. When the dashboard indicator light turned off, this meant that the engine was ready to start. The operator would turn the ignition key to the run position. If the vehicle's engine was warm from recent use, the glow plug wasn't needed and the operator could immediately start the engine.


Remote control cars, trucks, boats and airplanes also use a glow plug to start their engines. These nitro methanol-powered or gasoline-powered machines don't have spark plugs. As a result, glow plugs are used to ignite the engine.

Choosing the correct glow plug is relatively easy. It is designated by your year, make and model of vehicle. In remote-controlled cars, there is a large array of glow plugs to choose from that fit different hobby vehicles. Several factors indicate which to choose in which situation.

Smaller remote-controlled engines hold less heat and require a hotter glow plug for ignition. The reverse is true for larger remote-controlled cars — they hold more heat and do not require as hot of a glow plug to operate. The higher concentrated fuels also require hotter glow plugs so that the engine can combust correctly and burn the excess fuel off as it operates.



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Post 2

When I was in college, I wanted to buy an inexpensive car so I could drive to a job or shop in another town. I found a used car dealership that offered cheap transportation cars for college students. As it turned out, the dealer said he sold the last $400 car on the lot two hours before I arrived, but for a little bit more, he could help me finance a better car.

He pointed me in the direction of a horrible green sedan in the back of the lot. This was at a time when diesel cars were rare in the United States, so the only place to buy fuel was at truck stops out of town. He asked me if I knew anything about diesel engines, and I said no. He explained that the car had a glow plug that ignited the diesel fuel, almost like a cigarette lighter heating the end of a cigarette. I almost bought the car, but didn't like the idea of looking everywhere for diesel fuel. In retrospect, I'm glad I didn't buy that car. Now I would consider buying a diesel car, simply because most gas stations sell diesel fuel.

Post 1

I guess this is why diesel-powered trucks will idle for hours at truck stops and parking lots. It would be easier to keep the engine running rather than allow the glow plug to cool down completely.

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