Glow plugs are used in diesel engines to help heat the fuel in preparation for the combustion chamber when the engine is cold. They are powered using all 12 volts available from the battery, and are located on top of the cylinders. They are used frequently, and the duration of their use is determined by the weather conditions where you live. Cars in colder areas are likely to need new glow plugs much more frequently, while glow plugs in warmer areas can outlast 100,000 miles. With continuous use and extreme temperature variances, glow plugs are a hard working part. Rough starts or misfires while starting, smoking when starting, and trouble starting in cold conditions are all basic signs of a failing glow plug. They tend to be relatively cheap and are easy to replace with the right tools.
Part 1 of 1: Replacing your glow plugs
- Deep socket set and ratchet
- Replacement glow plugs
- Socket set
- Valve cover gaskets (if equipped and desired to be replaced)
Step 1: Disconnect the battery cable. Locate and disconnect the black negative battery cable. Any time you are working on an electrical system on your vehicle, disconnect the battery cable first. Glow plugs are routed to have the full 12 volts available from the battery.
- Note: Often when replacing parts such as glow plugs, there is a certain amount of digging that might be required in order to access the part. This varies greatly by make, model, and year. Keep track of anything and everything you remove or set aside when accessing the glow plugs on your vehicle. It is good practice to bag and label your screws and bolts.
Step 2: Remove the valve cover (if applicable). If the glow plugs are located under the valve covers, you will need to remove them first. If not, continue to Step 3. To remove the valve cover, unscrew all the retaining screws around the perimeter of the cover. Keep an eye out for the valve cover gaskets between the engine and the covers.
- Note: This is an excellent time to replace the valve cover gaskets on your vehicle.
Step 3: Locate the glow plugs. The glow plugs will be screwed into the cylinder head. Look for the top sticking out and the wire that delivers their 12 volt power supply.
Step 4: Disconnect the power supply to the glow plugs. On top there will be a nut, bolt, plastic terminal, or other type of connection device to remove the wire from the glow plug quickly. Unfasten the terminal and set the wires aside. Newer models will have a terminal similar to spark plugs. These can be pulled straight off (pliers help, but be careful not to break the terminal).
Step 5: Remove the glow plug. Use a socket and ratchet to remove the plug. Place the ratchet over the plug and turn to the left (counterclockwise). This may require a deep socket. These should come out clean for the most part. You will know by the length and shape of the plug how damaged it is (see picture below).
- Note: Glow plugs can break down inside of their compartment. If you are removing a broken plug, make sure to remove all broken pieces from the engine.
Step 6: Prepare to install the new glow plug. Now is the time to take a few precautions and possibly improve the parts associated with the glow plugs. Clean the area around the glow plug hole’s opening. If the supply terminal is dirty, use a wire brush or appropriate tool to clean it for a solid connection.
Step 7: Install the new glow plugs. Hand tighten them into position. Use your socket and ratchet to snug them into place. Be careful not to over-tighten them. It will cause damage to the plug, preventing them from working correctly, or possibly breaking the plug in its place.
Step 8: Attach the power supply. Reattach the wires that supply the glow plugs with power. These should screw or clip into place in exactly the same way you removed them in step 4.
Step 9: Replace the valve covers. Replace the valve covers or anything removed in the process of accessing the glow plugs. If you removed the valve covers, now is the time to replace the gasket between the cover and the valve block. Insert all of the screws removed with the valve box after you have swapped out the gasket. Tighten them by hand and then use your ratchet to tighten them down.
- Note: Some manufacturers require the valve screws to be torqued to a specific pressure. Look to your vehicle’s manufacturer for this information if dealing with valve cover removal.
Step 10: Connect the negative battery cable. Reattach the negative battery cable to the battery. This restores power to the vehicle and the glow plugs can be tested using a scan tool or multimeter if desired.
Glow plugs are demanded to turn freezing conditions in the engine to functional operating temperatures, and do it quickly. They are then required to shut off and cool down just as quickly. They are worked hard, considering the drastic changes in temperatures they endure during every use. It is common to have to replace them or the other parts associated with them. If you do not wish to replace your glow plugs yourself, trust a certified mechanic from YourMechanic for fast, friendly service at your home or office at your convenience.
This article originally appeared on YourMechanic.com as How to Replace the Glow Plugs in Your Car and was authored by Jessica Howe.