A glow plug is a long, thin piece of metal with a heating element at its tip. The heating element is made of materials that can withstand oxidation and high temperatures. In diesel engines, glow plugs are heating components that help with cold starts. When an electric current flows through them, their surface temperature rises, heating the surrounding fuel-air mixture and causing it to ignite.
In this reading, we’ll explore what a glow plug is, its function, diagram, types, and how it works. We’ll also learn its sign of failure.
Let’s get started!
What Is A Glow Plug?
A glow plug is a heating device used in diesel engines to help start them in cold weather. This metal device is shaped like a pencil and has an electric heating element at the tip. One glow plug per cylinder or one glow plug in the inlet manifold make up a glow plug system.
When starting the engine in older systems, the driver must manually turn on the glow plug system and wait for about 20 seconds. Modern systems have a shorter warm-up period and automatically turn on the glowplug or plugs before starting the engine.
Function Of A Glow Plug
The major function of a glow plug is to heat incoming fuel and air in a diesel engine to promote efficient combustion. Fuel combustion starts your engine, allowing you to drive. Each cylinder in your engine has one glow plug, which is located in either the pre-chamber (pre-chambered engines) or the combustion chamber (direct-injection engines).
Related: What Is a Diesel Engine? Its Diagram, Applications and Parts
Design & Diagram Of A Glow Plug
While glow plugs are available in a variety of styles, they usually share a common design. They often have a hexagon-shaped head and a thin, threaded center unit that make it simple to install and remove with a wrench. This thread makes sure the cylinder head fits snugly.
The heating element of the glow plug has a heating coil at one end. It is the component that heats the air-fuel mixture to help the engine start. The electrical connector is on the opposite end of the glow plug. This connection supplies the electricity required to operate the heating element.
Types of Glow Plug
There are different types of glow plugs, each designed for specific performance characteristics, environmental conditions, and engine types. Here’s a breakdown of the main types:
Pressure Sensors Glow Plug (PSG)
The sensor and electronics in the PSG pin optimize the performance of these types of glow plugs while also significantly reducing particle emissions. The modern PSG operates by using its built-in sensor to measure the pressure within the combustion chamber and then sending the information to the engine management electronics so they can calculate the proper heating pattern for the glow plug.
Ceramic Glow Plugs (CGP)
Built for high temperatures, it can reach temperatures of up to 1500°C in less than three seconds. Engines start faster because of this quick heating. When used in low-compression diesel engines that comply with EPA regulations, it is advantageous.
High-Tech Steel Glow Plug
There are two varieties: GE and GN. Modern three-phase glow plugs, known as GN plugs, heat up rapidly, hold their heat while being ignited, then cool down in three minutes. The plugs resemble a long pencil. Modern high-tech steel plugs heat up in seven seconds, compared to the thirty seconds or more that older diesel engines need to heat up when using GE-type plugs. Generally speaking, GE plugs are smaller and resemble spark plugs more in size.
Related: What Is A Spark Plug? its Functions, Diagram And Parts
How A Glow Plug Works
A glow plug is only required during the ignition process, as opposed to a spark plug, which operates constantly as you drive. The glow plug gets its name from the way it heats up and creates visible light by energizing the heating element.
When fuel is injected, the intake air is compressed before the fuel injector spray distributes fuel onto the glow plug’s hot tip. Even when the engine is cold, the injected fuel mixes with compressed air, evaporates, and nearly immediately initiates combustion.
Symptoms Of A Bad Glow Plug
Bad or failing glow plugs can significantly impact the performance of a diesel engine, especially during cold starts. Since glow plugs help heat the air in the combustion chamber for smoother ignition, any issues with them can lead to a variety of symptoms. Below are the common signs that indicate a bad glow plug:
White or Black Exhaust Smoke
Pouring white and black smoke from the exhaust is not a good indication. When there is insufficient heat in the engine to effectively ignite the fuel, white smoke is produced. The unburned fuel particles then smell like diesel fuel when they leave the engine through the exhaust. The air and fuel mix being wrong, usually with too much gasoline, is what causes black smoke. Problems with glow plugs exacerbate all of these issues.
Rough Idling
When the engine eventually starts, it will idle roughly and emit white smoke from the exhaust for several minutes. This is a sign that one or more glow plugs have burnt out, become carbon-fused, or are broken. Inspect the timing of the fuel injection if all of the glow plugs are burnt at the tips.
Difficult To Start
Most often, difficulty starting an engine is a sign of broken glow plugs. Without properly functioning glow plugs, the combustion chamber could not warm up sufficiently in cold weather to ignite the fuel and start the engine.
Engine Misfiring
High compression ratios and precisely timed and controlled fuel injections are necessary for the combustion process in diesel engines. This causes the diesel fuel to ignite and burn. Problems with fuel quality, compression, and fuel injection can result in misfires.
Compression pressure and glow plug heat are the sources of the combustion chamber’s heat. For ignition to occur, it must achieve a minimum temperature of 450°F, or 232°C. The engine chamber won’t get hot enough if the glow plugs aren’t working properly.
Bad Fuel Efficiency
Glow plugs aren’t usually the main element affecting fuel economy; there are other aspects to consider as well. However, glow plugs could be the cause if you’re experiencing some of these other symptoms and your fuel economy is significantly lower than normal.
Glow Plug Replacement Costs
A glow plug replacement typically costs between $242 and $296. Parts range in price from $100 to $117, and labor expenses are projected to be between $142 and $180. This range does not account for your particular area or for taxes and fees.
What is the typical lifespan of glow plugs? 80,000 to 100,000 miles is the typical lifespan of a glow plug, however this might vary depending of the brand, quality, and driving habits. You may be sure that your new glow plugs will be reliable for a while if you’re wondering how long they will last.
FAQs
Should I drive if my glow plugs are broken?
No, using a malfunctioning glow plug while driving is not safe. An incorrect combustion chamber temperature can cause insufficient fuel ignition, causing your engine to misfire or run rough. If you are traveling in unsafe conditions or at high speeds, this might potentially put you in danger.
Is replacing glow plugs a difficult task?
Even though cars have gotten more complicated over time, you can usually still change your car’s glow plugs on their own. Make sure you have the appropriate glow plugs for your car and a manual torque wrench before starting the task, though.
What happens if a glow plug malfunctions?
When the engine eventually starts, it will idle rough and emit white smoke from the exhaust for many minutes. This is a sign that one or more glow plugs have burnt out, been carbon fouled, or are broken.
A diesel without glow plugs—will it start?
No, on a chilly day, the diesel engine needs glow plugs to provide the first bit of heat in order to start. They serve no other purpose than this. If it’s warm outdoors, they will start without them as well. This is a condition indicator for diesel engines.