General Truck Repair
April 11, 2022

Truck Repair DIY Blog Series: Changing Your Truck's Glow Plug

Glow plugs are unfamiliar to many new diesel truck owners. Continue reading to learn more about how they function. You'll be pleased you took the time to do so.

Truck glow plug being changed

Diesel truck sales are steadily rising as a viable alternative to standard gasoline engines. Diesel engines are no longer known for being noisy and odorous. Diesel trucks are quieter and environmentally friendly thanks to modern technology and regulations and smart glow plugs.

There are a few key distinctions between gas engines and diesel engines that lead drivers to select diesel. Diesel trucks have higher torque and hauling capacity than gas trucks, as well as more excellent gas mileage.

On the other hand, glow plugs are unfamiliar to many new diesel truck owners. Continue reading to learn more about how they function. You'll be pleased you took the time to do so.

What are glow plugs & how do they work?

The spark plugs in a gas engine start the engine by creating a spark that ignites a gas and air combination, generating power for the motor. The purpose of a glow plug is to heat the diesel fuel under pressure so that it may self-combust. This function does not need the use of a spark.

Glow plugs are tiny heaters found within diesel engines' hoods. A varied number of glow plugs are required for each make and model of diesel engine, and this is because each cylinder requires one glow plug, and each engine has a different number of cylinders.

A glow plug is a heating coil that is put into a tube. It has a pencil-like form and resembles a spark plug. It's commonly constructed of metal with high heat resistance, such as platinum or iridium. It features a temperature sensor on one end and a heating element.

Screw-in holes and a single-pole connection pin soldered to the housing with a non-releasable metal nut characterize the glow plugs. Glow plugs are commonly found in the pre-combustion chamber or the combustion chamber of a diesel engine. Glow plugs work by combining heat and pressure. iesel engines need heat to start, which is particularly important in cold weather.

Steps to replace glow plugs

Here are the steps that you will need to follow to replace your truck's glow plugs. Make sure that you follow these steps and get the job done. 

1. Disconnect the battery cable first

Disconnect the black negative battery cable by opening the hood. This is an important safety measure because glow plugs pull voltage from the battery. You may require a tool to release the nut that links the cable to the negative terminal.

2. Take off the valve cover

You'll need to remove the valve cover if your glow plugs are covered by one. Remove the retaining screws around the outer edge of the cover and inspect it for damage before replacing it.

3. Disconnect the glow plug wires

The glow plug wires must be disconnected. The glow plugs are located in the cylinder head and are linked to a wire that supplies the voltage power source. Nuts, bolts, terminals, or other similar connection devices will be used to connect the wires to the plugs.

4. Discard the glow plugs

Using a socket and a ratchet, remove the glow plugs. Place the ratchet over each plug and rotate it clockwise. To release the plugs, you may need to attach a deep well socket to the wrench.

You'll be able to assess the condition of each glow plug once you've removed it. Glow plugs may break down once fitted, so ensure you get all the components out of the engine before removing a damaged one.

5. Put the new glow plugs in place

Install the new glow plugs by hand, placing them and tightening them with a wrench in a counter clockwise motion. Overtightening the plugs might cause them to shatter, so be cautious.

6. Reconnect the cables

Reconnect the glow plug wires, securing the nuts, bolts, or terminals. Reinstall the valve cover. This is where you should read your truck's owner's manual to see whether the valve sockets need to be torqued to a certain pressure.

Connect the battery cable and start your engine to test your new glow plugs. You may also test your plugs using a scan tool.

When should your glow plugs be replaced?

Inside your engine, an entire relay of glow plugs is ready to heat the diesel fuel and initiate the ignition process. As previously stated, the number of glow plugs will be determined by the number of cylinders in the engine. It might be simply one glow plug or the electrical system that links the glow plugs if you start experiencing trouble with them.

Here are several indicators that your light plugs are malfunctioning.

- You get a warning light 

Many diesel-powered trucks include sensors that will alert you if there is a problem. A Check Engine or Check Glow Plugs light may be illuminated. The Check Engine light will be illuminated by a defective glow plug, as will various other issues. Therefore this warrants further diagnostics and does not necessairly indicate that the problem is with the glow plugs.

- You have issues with starting the engine 

To start a diesel engine, heating glow plugs are needed to provide the requisite heat. Without this heat, your truck will not start. The problem may be with the battery or the fueling system, so check them first.

- You can see smoke coming out 

If your diesel engine operates correctly with adequate combustion processes, you should never see black smoke coming from the exhaust pipe. If your glow plugs fail, the fuel in certain cylinders may not be adequately heated, resulting in black smoke. Glow plugs that aren't working aren't the sole cause of black smoke, so don't count out other possibilities.

- Slow acceleration 

Even if your glow plugs are damaged, your truck will start. However, since not all cylinders are getting warm gasoline in the same manner, your acceleration will be reduced. You may also have misfiring issues with your engine. Don't rule out alternative possibilities if you don't experience any of the other symptoms mentioned below.

Final words

Now you know how to identify problems with glow plugs and fix them. Ensure that you adhere to this guide and get the job done correctly. 

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