The design of the diesel engine is not the same as that of the gasoline engine. One of the biggest differences is that it uses a Glow Plug instead of a Spark Plug. The two components act completely differently and cannot replace each other. The task of the glow plug is to heat the air in the combustion chamber so that the diesel fuel can be ignited smoothly in cold weather. It is a cold-weather start aid. In most cases, glow plug replacement is something you can still handle on your own.
Glow Plugs Help Start The Diesel
Relying on compressing air to a very high temperature, diesel engines ignite on their own. But on a cold day, the icy cylinder will suck up heat, and the engine will be hard to start. At that time, the glow plug quickly heats up to a very high temperature before starting, helping the fuel to ignite and making the engine easier to start. In general, the number of glow plugs is equal to the cylinders.
When Should You Consider a Glow Plug Replacement?
Usually, a failing glow plug doesn’t die right now. It has some warning signs as its performance is down. Paying attention to these symptoms can help you resolve the problem before the engine won’t starting.
Glow Plug Light Flashing
Most modern diesel vehicles have a glow plug light on the dashboard. It looks like a small coil. When you turn the key, this light comes on for seconds because the glow plugs are heating up. If the glow plug light flashes or stays on for a long time, it’s a signal that there’s a problem in the glow plug system.
Check Engine Light On
If the glow plug breaks, or if there is a problem with the line, it may light up on the dashboard “Check Engine Light”. The onboard diagnostic system (OBD) detects the resistance value of each preheating plug and, once one or more of them are outside the normal range, records a fault code (say P0380) while a warning light is lit to remind you.
Hard Starting
This is the most common case. If the glow plug cannot heat the combustion chamber normally, the engine will be difficult to operate in cold weather. You may have to twist the key several times before the engine barely “puff” sound. If the battery and fuel system are fine, there’s a high probability that the glow plug is out of order.
Misfiring During Startup
After the engine starts, it may run unevenly or misfire within the first few minutes. This is because one or more cylinders cannot ignite properly due to insufficient heat. The engine could actually only run on part of the cylinder until the heat from the combustion of the working cylinder warmed the whole engine up.
Rough Idling
Similar to misfires, if the glow plug burns out or has significant carbon deposits, the engine may become unsteady when idling, jitter, or jitter, especially after a cold start. This instability usually gradually improves as the engine heats up and sustains combustion on its own, but this is clearly a sign of a potential problem.
Decreased Fuel Efficiency
Poor glow plug performance indirectly affects fuel economy. The engine can not achieve full combustion during warm-up. The engine control unit (ECU) may adjust the amount of fuel delivered. This means that the engine has to consume more fuel than it actually needs. Especially during short runs, the engine has not yet fully reached operating temperature, which is more common.
White or Black Smoke When Starting
- White smoke: When starting up, you see white smoke coming out because the diesel is not burned. The combustion chamber temperature is too low, the diesel fuel can not be ignited, and turns into a visible mist. This white smoke has a pungent smell of diesel fuel.
- Black smoke: Black smoke indicates incomplete combustion and the wrong ratio of oil to air. If there is a problem with the electric heating plug, the diesel fuel will not burn clean, soot will form, and black smoke will come out of the exhaust pipe.
How to Do a Glow Plug Replacement?
Glow plug replacement is easy; just prepare the tools and take your time. Be careful not to push too hard; the most common thing is to break it by getting stuck in the head.
Preparation and Safety
- Work on a Cool Engine: it is easier to unscrew a tight-stuck glow plug when the engine is slightly warmer. But too hot can burn people. Be sure to wait until the engine cools down completely before you do it.
- Disconnect the Battery: Unplug the negative wire of the battery first to avoid a short circuit or electric shock.
- Gather Your Tools: You will need a socket set with extensions and a universal joint, a torque wrench, needle-nose pliers, and a reamer tool for cleaning the glow plug bores.
- Clean the Area: Clean the dust and debris around the preheated plug with compressed air or a small brush. Do not do anything to fall into the cylinder.
Removing the Old Glow Plugs
Seized glow plugs are common, too much force will snap them.
- Access the Plugs: Remove the engine hood, intake pipes, or other components that block access to the glow plugs.
Disconnect Electrical Connectors: Carefully remove the wire or lid from the top of each glow plug. They may be pulled off or caught in small nuts. - Apply Penetrating Oil: If the engine is old, or the glow plug has not changed for a long time, please spray some high-quality penetrating oil at the bottom of each glow plug. Let it soak for a few hours; better if it stays all night. This can greatly reduce the risk of breaking the slow plug when screwing.
- Carefully Loosen: Using a properly sized deep socket and a ratchet, attempt to loosen the glow plug by turning it counter-clockwise. Don’t push too hard; stop first if it feels tight. You can tighten it a little first and then loosen it in the opposite direction, which can help remove some rust. If you still can’t twist it, spray some more penetrating oil and wait a little longer. Remember not to exceed the torque specified by the manufacturer.
Installing the New Glow Plugs
- Clean the Bore: After removing the old glow plug, clean the holes and seats in the cylinder head. The carbon deposits inside can be scraped off with a reamer with a bit of grease. After the hole is cleaned, the new glow plug can be more stable, and the heat transfer is better.
- Hand-Thread the New Plug: Slowly screw the new glow plug into the cylinder head by hand, so as to avoid misalignment of threads. After screwing on for a few laps, it means you’re on the right track when you feel smooth.
- Torque to Specification: Use a torque wrench to tighten the preheating plug according to the strength specified by the manufacturer. Tightening may make the glow plug break. Tightening may cause poor heat dissipation, large vibration, and easy damage over time.
- Reconnect and Reassemble: Reattach the electrical connectors to the new glow plugs, ensuring a snug fit. Reinstall any engine components you removed earlier. Finally, reconnect the negative battery terminal.
Note: For glow plugs with a threaded terminal for the electrical connection, there is a specific, much lower torque value for the small retaining nut. Over-tightening this nut can break the terminal. Always refer to the specifications on the packaging or in your service manual.
How Much Does It Cost to Replace a Glow Plug?
If you do it yourself, it probably won’t cost much more than $65-$70. If you have it done professionally, the price may be closer to $300, including parts and labor.
| Car Make | Estimated Average Cost |
|---|---|
| Volkswagen Jett | $280 |
| Ford | $850 |
| Chevy Silverado | $680 |
| BMW | $980 |
| Mercedes-Benz Sprinter | $600 |
| Jeep | $550 |
About FridayParts Glow Plugs
As routine maintenance, regular detection and glow plug replacement will help extend the life and efficiency of diesel engines. FridayParts offers high-quality, affordable glow plugs for a variety of diesel vehicles and heavy equipment. A wide inventory ensures that you can find the right parts. Shop now!
FAQ:
Replace one glow plug or replace all?
It’s better to replace all the glow plugs at once. Like spark plugs, they wear out at about. If one is broken, most of the others are almost reaching the end of their lives. One full transducer saves the trouble of repeated disassembly and assembly later and the labor cost.
How often should you change glow plugs in a diesel engine?
Generally, the glow plugs on a diesel engine last for at least 5 years or about 100k kms. But it is dependent on usage. Since most diesel engines need heating only during morning cold start and later on when the engine is hot, they start without heating using a glow plug, provided engine compression is good.
Can a transmission fail from bad glow plugs?
No, but if your trans is an automatic, the transmission will probably hold out on upshifts to a higher speed because you are stepping into the throttle more to overcome the miss and the throttle position sensor will relay this back to your transmission computer.
Can you drive a diesel with a bad glow plug?
Yes, if you can start the engine ok in a short period of starter use. Starting a diesel with bad glow plugs may cause prolonged starter use and overheat the starter or cables, or the battery. Avoid prolonged starter use. Once the engine starts, it may run rough till it warms up, but the glow plugs are no longer needed and the vehicle is safe to drive anywhere.
Can a broken glow plug damage the engine?
That’s right, and that’s the biggest risk when removing the glow plug. If the tip breaks and falls into the combustion chamber, it can severely damage the engine. Metal fragments can hit the piston and cylinder head, break the piston, valve and cylinder wall, and eventually the entire engine may have to be rebuilt or replaced.
