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Diesel engines are designed different than gasoline-based engines. One of the most significant differences is diesel engines have glow plugs instead of spark plugs. Spark plugs create a spark that ignites the fuel to power the vehicle. Glow plugs rely on compression rates to raise air temperature to the point of spontaneous combustion of the diesel fuel. To save money, here are a few tips on how you can change your own glow plugs.
Steps
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Find the glow plugs in the engine compartment.- They are usually on top of the cylinder head.
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Remove the glow plug wires.- The glow plug wires are beneath the engine's valve covers. You will find one end attached to the top of the glow plug and the other attached to the engine. Remove the wire attached to the glow plug. Remove the small nut that holds the wires to the glow plugs with a wrench. Push the wire aside. Repeat this process to remove each glow plug wire.
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Clean each electrical contact and nut.- Similar to battery contacts, glow plug wires can become dirty, which can result in a poor electrical connection.
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Use reamer and ream the glow plug hole for each glow plug. [3] X Research source- This is just to clean out the glow plug hole, so ream only long enough to remove any buildup.
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Replace each plug and tighten them down with a ratchet.- Tighten them just to the point of slight resistance. If you tighten them too much, the next time you need to change the glow plugs you might break one off trying to remove it. This can result in a costly repair.
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Reattach the electrical wires to each glow plug with a nut using the wrench.
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What Should You Know Before Replacing Glow Plugs?
Expert Q&A
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QuestionHow do I test a glow plug?Charley Helvy is an Automotive & Diesel Expert based in Avondale, Arizona. He is the founder of Charley’s Garage, an educational YouTube channel focusing on simple videos for automotive and truck enthusiasts. He has over 31 years of experience in the automotive world. He is a Diesel Instructor at the Universal Technical Institute and is a certified ASE Master Heavy Truck Technician. He offers training on gas and diesel engines on his YouTube channel, along with other DIY and explanation videos for beginners and enthusiasts alike. In 2024, he published a complete guide on Emissions Systems in Automotive and Diesel Vehicles.To properly test a glow plug, understand that it functions as a self-grounding heating element where voltage is applied. Similar to any heating element, the resistance within the glow plug generates heat when current passes through it. Since resistance relates to amperage, the most accurate method to assess its functionality is by measuring the amount of current the glow plug draws. Checking for voltage alone at the glow plug is insufficient, as it merely confirms the presence of voltage and not the functionality of the glow plug itself. Instead, measuring the amperage the glow plug draws provides a reliable indication of its operational status.
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QuestionGlow plugs won't come off, what should I do to remove them?Charley Helvy is an Automotive & Diesel Expert based in Avondale, Arizona. He is the founder of Charley’s Garage, an educational YouTube channel focusing on simple videos for automotive and truck enthusiasts. He has over 31 years of experience in the automotive world. He is a Diesel Instructor at the Universal Technical Institute and is a certified ASE Master Heavy Truck Technician. He offers training on gas and diesel engines on his YouTube channel, along with other DIY and explanation videos for beginners and enthusiasts alike. In 2024, he published a complete guide on Emissions Systems in Automotive and Diesel Vehicles.Sometimes, when a glow plug fails, the tip may swell and expand. This can cause difficulties in removing the glow plug, as the hole it fits into may become smaller due to the expansion. In such cases, you may need to break off the tip of the glow plug to facilitate its removal. This can leave the broken tip in the combustion chamber, posing a challenge. There are two methods to address this issue. One approach, as outlined in military manuals, involves cranking and rotating the engine until the broken tip is expelled. However, this method carries the risk of damaging valves and cylinder walls. Alternatively, you may need to remove the cylinder head to extract the broken piece from the combustion chamber. When changing glow plugs, it's ideal that none of them have expanded tips that could break off, simplifying the replacement process.
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QuestionCan I change glow plugs myself?This answer was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness.wikiHow Staff EditorStaff AnswerFor most vehicles, yes. You just need to make sure you have the right kind of glow plugs for your car, as well as the appropriate tools, such as a manual torque wrench.
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Things You'll Need
- Ratchet set
- Wrench
- Screwdriver to pry off electric cord in the event of corrosion
- Glow plug chamber reaming tool
- New glow plugs
References
About This Article
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Reader Success Stories
- "Helping a friend with glow-plug trouble. Learned how they worked, change, test. Good stuff. Note: when testing with meter and you get no reading, that is an open glow plug; burned out would show a solid short." ..." more
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"Helping a friend with glow-plug trouble. Learned how they worked, change, test. Good stuff. Note: when testing with meter and you get no reading, that is an open glow plug; burned out would show a solid short."
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"Tried to verbally explain a mechanical procedure to my grandson which was difficult. These pictures and professional advice saved the day. Thank you."
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