6 Common Bad Glow Plug Symptoms In Cars – How to Fix

Glow plugs are used to generate a spark in diesel engines when it is too cold since diesel engines lack ignition systems and any form of the spark plug. Diesel glow plugs are frequently damaged and continually exposed to high temperatures. As a result, you must frequently replace them.

A diesel engine may have up to 10 glow plugs, one for each cylinder, due to the engine’s prolonged exposure to high pressures and harsh temperatures. If only one of them fails, you could not comprehend. However, the engine will be challenging to start if three or more are defective. A bad glow plug can shorten the life of a diesel engine.

However, because the majority also have glow plug relays, you may not be aware of any bad glow plugs. Some cars come with PCMs that monitor glow plug performance and report the whole actions of every plug.

Common bad glow plug symptoms include trouble starting, illumination of the check engine light, an abundance of white smoke, and a considerable drop in engine performance.

In contrast to gasoline engines, a diesel engine’s combustion system needs a heating element to warm the air-fuel combination and prepare it for combustion. The glow plug is the name of this component.

The glow plug will eventually need to be replaced because it won’t survive indefinitely due to early wear. If you have a bad glow plug, it must be changed right once to avoid unfavorable effects, especially those linked to starting problems.

You must be well-prepared for any bad glow plug symptoms as a driver of a diesel car. Early diagnosis of these symptoms can save you a lot of money on repairs while also averting serious repercussions. You also avoid putting yourself in a position where you are stranded in a location without access to assistance and a running automobile.

Glow Plugs: What are They?

Glow plugs might be compared to the tiny heaters found beneath your car’s hood. For proper combustion, these heating components warm the diesel and air in your car’s engine. While glow plugs and spark plugs perform similar tasks, their main distinction is that glow plugs use heat to ignite fuel and air to start diesel engines.

1. A standard glow plug
A standard glow plug by Donar Reiskoffer / CC BY 3.0. Diesel engines lack ignition systems and any kind of spark plug, therefore when it’s too cold, glow plugs are utilized to create a spark.

Every diesel engine has a glow plug for each cylinder, which explains why various models and manufacturers need various numbers of glow plugs.

A glow plug is created by inserting a heating coil into a metal tube. This tube is sealed at one end and contains ceramic powder, which is electrically insulating. The heated tip of the glow tube may quickly reach 1000°C if electrically charged.

Ceramic glow plugs can be substituted with regular plugs. They are filled with a heating element, which is subsequently covered in silicon nitride or ceramic. The glow plugs may heat up rather rapidly and maintain higher temperatures for extended periods because of the shell.

High-quality glow plugs in good condition significantly reduce exhaust gas emissions, preserving minimal environmental effects.

Where are the Glow Plugs Located In a Car?

The cylinder head of the engine houses the diesel glow plugs. They are separately screwed onto each cylinder. The battery supplies 12 volts to power each glow plug.

They will have a wire carrying electricity attached to the top that will jut out, making them easy to see. To access the glow plugs, you might occasionally need to remove the valve cover.

Glow Plugs: How Do They Work In a Car?

Spark plugs do not need to be hot enough under pressure to self-combust like glow plugs do. In warm conditions, gasoline may accomplish this with little assistance from other parts of the car. Diesel engines, meanwhile, frequently struggle to burn gasoline in colder climes. For the engine to start, the glow plugs warm up the gasoline.

To start the engine, the intake air is compressed, and when the piston rises, the engine forces diesel into the ignition chamber. The fuel evaporates and burns when combined with air. Many people think that evaporation and igniting are happening simultaneously since they begin practically immediately after.

When an engine is started, a 3-phase process for glow plugs is required.

  • Pre-Heating phase: The engine is propelled to stand by the diesel glow plugs, which warm up fast.
  • Maintenance of Temperature phase: The glow plugs must keep their internal temperature constant for optimal combustion.
  • Post-Heating phase: Once the engine has been started, the diesel glow plugs continue to heat up for a few minutes to keep the combustion process continuing.

What are the Typical Bad Glow Plug Symptoms?

Glow plugs aren’t meant to last a lifetime. Glow plugs can become broken, leading to unfavorable results that could cause your car to become stranded in the middle of nowhere without being able to start it. This is because diesel engines are regarded to some extent as heavy-duty.

The good news is that before the glow plug fails, your car will warn you if it is. The bad glow plug symptoms frequently start to unfold. Such symptoms include:

1. Troubles in Starting the Engine

Have you ever heard that diesel engines struggle to start when they are cold? Thanks to the glow plug, the issue has been resolved.

2. A glow plug being tested outside an engine
High-amperage battery chargers, which are devices intended to facilitate engine starting, are another frequent cause of glow plug failure. These chargers are capable of producing voltages so high that the glow plug tips may explode.

But without aid from the glow plug, the diesel engine will be utterly incapable of burning the air-fuel combination because it is too cold.

Having several defects or malfunctions in various glow plugs will prohibit your diesel engine from starting, even if one broken glow plug shouldn’t.

2. The Check Engine Warning Lights Turn On

Modern automobiles come with several systems that enable any glow plug issues to activate specific warning lights. Your vehicle’s internal computer receives the indication that the glow plug isn’t functioning properly from the control module in charge of monitoring the glow plug’s functionality. At this point, the motorist ought to be aware.

The glow plug has to be replaced to rule out other potential causes for the check engine light to appear.

Use an OBD 2 scanner to accomplish this, which can read any internal issue through codes and transform it into something useful on the screen. If you don’t have sophisticated OBD 2 scanners, you risk not understanding the meaning of the code; in this case, you should look it up online. You may find a ton of materials on Google that can assist you in translating the error code produced by the computer in your car.

Once a bad glow plug has been identified as the source of the issue, the following step is to install a new one right away to restart your car as soon as feasible.

3. The Car Produces  Large Amounts of White Smoke, Particularly When Starting the Engine

It’s OK to see a small amount of white smoke emerging from the vehicle’s exhaust system and to consume cold starters. But at this time, you should be concerned if the white smoke increases excessively and you start noting that it’s more than usual.

Any white smoke suggests that there is some fuel in the combustion system that has not yet been burned. Given that we are dealing with diesel engines, the issue most likely stems from the glow plug’s warm air-fuel combination.

It’s crucial to keep in mind that white smoke might also result from a coolant leak into the combustion system, which may be connected to a damaged cylinder head.

Therefore, before making any attempts to repair the glow plug, you must first run a complete diagnostic on your car to ascertain if the issue is caused by a bad glow plug.

4. Performance of Your Engine Is Drastically Reduced

The glow plugs’ work does not finish when the engine is started since they are in charge of heating the air-fuel combination. Throughout the driving operation, they are increasing the temperature as needed.

As a result, you will notice a sharp decline in engine performance if one or more glow plugs are destroyed. The engine may occasionally be noisy, especially while it is idle.

As we previously said, you must ascertain if the problem is caused by a bad glow plug because the majority of these symptoms might be attributed to other malfunctioning parts.

5. Decrease In Fuel Economy

The engine will believe there is insufficient gasoline when the glow plug isn’t functioning correctly since a lot of fuel won’t be entirely burned, leading it to request more fuel from the pump.

Pumping more gasoline while generating little energy results in a large decrease in fuel efficiency, which corresponds to the bad glow plug.

Once more, a drop in fuel economy might be attributed to many different factors. So, the first step is to make sure the issue is with the glow plug and not another component, before replacing it.

3. Glow plugs beneath the contact bar

Glow plugs beneath the contact bar by Dana60Cummins / CC BY-SA 3.0. The diesel glow plugs are located in the cylinder head of the engine. They are each individually fastened into a cylinder. Each glow plug is powered by a 12-volt supply from the battery.

6. A Misfiring Engine

The air-fuel combination won’t burn in diesel engines until it reaches a temperature of 450 degrees Fahrenheit, or 232 degrees Celsius. This temperature is easily attained by the air-fuel mixture thanks to compression and heat from the glow plug.

However, if the glow plug is malfunctioning, the air-fuel combination won’t heat and your engine may misfire, resulting in an error.

Keep in mind that engine misfiring is another issue that may be related to some internal difficulties, and it may be very difficult to determine the true reason for engine misfiring. You should visit a qualified technician to evaluate the car because it might be a mix of several internal problems.

What Causes Bad Glow Plug Symptoms In a Car?

You shouldn’t be shocked if your car starts getting less mileage for petrol after displaying other warning indications.

Glow plugs often last a long period, however, occasionally they will stop working considerably earlier than expected. Some of the major reasons why glow plugs fail to include the following:

  • You installed the incorrect type of glow plugs.
  • The extended power supply (probably as a result of a stuck relay).
  • The voltages used by your engine are rather high.
  • The pistons are defective.
  • The valves are defective.
  • A piston ring is stuck.
  • Leaky injectors lead to corroded glow plugs.

Glow plug failure is also frequently caused by high-amperage battery chargers, which are tools designed to improve engine starting. These chargers can generate voltages that are so high that the glow plug tips will blow up.

Choose an intelligent battery charger if you wish to prevent this problem. Battery chargers are a significant financial commitment, so be sure to be well-informed before purchasing one.

Helpful hint: It’s not normal wear and tear if all the glow plugs break at the same time. They were harmed specifically by something.

How Can I Diagnose the Bad Glow Plug Symptoms?

The following instruments are needed to check for bad glow plug symptoms:

  • A Digital Multimeter
  • The Basic hand tools set
  • A Flashlight
  • The Service Manual
  • A Paper and a pen

Step 1:

Find out the multimeter’s resistance value. Determine the resistance of the digital multimeter before testing the terminals. Set the multimeter’s settings to read in Ohms and turn it on to do this.

4. Glow plug indicator light
The air-fuel mixture won’t heat up if the glow plug is damaged, and your engine might misfire and cause an error.

Ohms are represented by the “omega” symbol. Its representation is the upside-down horseshoe-shaped sign ().

Connect the multimeter’s two leads after setting it to Ohms, then examine the resistance reading it displays. Try changing the multimeter’s settings and setting it to a greater sensitivity if you receive 0. Do it repeatedly until you receive a reading.

Write down this figure since you’ll need it later for some crucial computations.

Step 2:

Within the engine, locate the glow plugs. A thick gauge wire, similar to the wire on a typical spark plug, is attached to glow plugs, which are installed within cylinder heads. Remove any coverings you may have as they may be blocking your access to the glow plugs. If more lighting is required, use a flashlight.

Step 3:

Glow plug wires should be disconnected. Once all of the glow plugs have been discovered, remove any caps or wires that are connected to them.

Step 4:

Use the multimeter to join the negative leads on the automobile battery’s negative terminal. To keep the lead attached to the terminal, try to tuck it inside. Alternatively, you may keep it in place by slipping it beneath the clamping device.

Step 5:

Repeat step 4 but use the positive terminal this time. Connect the positive lead of the multimeter to the terminal of the glow plug.

Step 6:

Keep track of the glow plug’s resistance. Note the resistance measurement that appears on the multimeter once both leads are connected to the terminals. Once more, the reading should be expressed in Ohms ().

Make sure that the negative lead is still attached to the negative battery terminal if there is no reading when the glow plug is touched.

Step 7:

Calculate the actual resistance. Subtracting will enable you to achieve it. By acquiring the resistance value of the multimeter in Step 2 and deducting it from the resistance value of the glow plugs, one may ascertain the real resistance of a glow plug.

Step 8:

Investigate the resistance value. Compare the genuine resistance value that was measured to the manufacturing specification. The diesel glow plug has to be replaced if its acquired resistance exceeds or falls short of the permitted standard.

Advice: The acceptable range for resistance value for the majority of glow plugs is between 0.1 and 0.6 Ohms.

Step 9:

Once all of the glow plugs have been checked, repeat for the remaining ones. It is recommended to replace the complete set even if one of the light plugs fails the test.

If there is a significant difference between the resistance measurements, changing just one or a few diesel glow plugs might result in engine issues comparable to a bad glow plug.

5. Bad glow plugs lead to engine misfire
Bad glow plugs lead to engine misfire by 天然ガス / CC BY-SA 3.0. If one or more glow plugs are damaged, engine performance will noticeably deteriorate. There may be times when the engine is noisy, especially while it is idling.

As long as you have clear access to the glow plugs, testing the resistance of a glow plug is often an easy task. However, any competent vehicle technician should be able to do this service if they are in a more private area if they are uncomfortable with the procedure. If necessary, they may also replace the glow plugs to restore your car’s operation.

You will need a few tools, including a universal joint and ratchet wrench set, deep sockets, screwdrivers, a glow plug connector remover, an installer, 6-point combination wrenches, valve cover gaskets, a glow plug chamber reaming tool, and some penetrating lubricant if you have some mechanical know-how and want to replace the diesel glow plugs yourself.

Gather all required equipment and materials in one location before beginning, and carefully read the directions. This is delicate work; don’t be haste and miss or skip any of the processes.

Keep in mind that instructions are meant to be broad and should work with the majority of diesel engines. For thorough instructions specific to your car, it is advisable to refer to your repair manual.

Bad Glow Plug Replacement Guide

When dealing with machinery, safety should always come first. Exercise caution when near hot, sharp, or hazardous things. Never replace equipment unless you are certain that doing so won’t jeopardize your car’s performance or safety.

Additionally, since fuel and fumes are connected to automobiles, keep open flames and smoke away from the work area. It’s also a good idea to keep a fire extinguisher close by in case a gasoline fire occurs.

After reviewing the essential safety guidelines, make sure to consult your vehicle’s owner’s handbook. That ought should draw your attention to where the diesel glow plugs are. To alter them, adhere to the following steps:

  1. Pull the valve cover off.
  1. Get rid of anything blocking your path to the glow plugs.
  1. Remove the intake manifold glow plug and the electrical connector.
  1. To remove the glow plug fastened to the cylinder head, use a combination wrench or deep socket. Don’t break it!
  1. Attach the glow plug reamer completely to the glow plug opening.
  1. Replace the glow plugs with the new ones.
  1. Hook up the connection and the glow plug terminal.
  1. If necessary, replace the valve cover as well.
  1. Any parts that were taken out so you could get to the glow plug should be put back in.

You’re finished! It is as easy to do as changing a spark plug. Depending on what is preventing access to the glow plugs and valve cover removal, it will take around an hour on certain engines while it might take up to five on others.

How Much Does a Bad Glow Plug Replacement Cost?

The price to replace a bad glow plug is between $235 and $282. Even if the cost of the item itself is between $93 and $102, labor costs are a significant factor and vary from $142 to 179 dollars.

Because the hourly fee at a small repair shop is far lower than at a dealership, many drivers choose to go there for repairs. However, owners of contemporary automobiles visit the dealership because they think the dealership will have qualified mechanics who are extremely familiar with the vehicle and won’t cause any significant difficulties.

6. Bad glow plugs trigger the Check Engine Light
Bad glow plugs trigger the Check Engine Light by Wikiuser100000 / CC BY-SA 3.0. Modern cars are equipped with several mechanisms that allow distinct warning lights to be activated in the event of a glow plug issue.

However, some drivers might even go one step farther and change their glow plug independently at this point. While labor expenses could be greatly reduced, you must be extremely cautious about whether you can do the task on your own or not. The diesel engine is a costly component that is susceptible to serious harm from any error.

The majority of automotive professionals claim that no DIY project works the first time, therefore if you have never replaced a glow plug before, you shouldn’t try it on your car to avoid dealing with unfavorable repercussions.

When Should the Bad Glow Plugs Be Replaced?

Glow plugs are one of your car’s extremely robust parts, so you won’t need to worry about changing them until 100,000 miles, according to automotive experts. This glow plug cannot progressively turn after 100,000 miles before needing replacement.

It’s also important to mention that changing the glow plug is not a difficult problem and doesn’t cost a lot to fix. Consequently, I shouldn’t worry too much about blowing all of the budgets that arrived, even if you’re dealing with a circumstance where the glow plug needs to be replaced.

Is It Safe to Drive a Car with Bad Glow Plug Symptoms?

Even while a bad glow plug won’t stop your car from starting or moving, it’s never a good idea to overlook the problem because it might lead to additional issues that you’d rather avoid.

Because your car won’t start if you have a lot of bad glow plugs, things become more difficult. This is a crucial circumstance, particularly if you’re starting on a chilly day or in a place where there isn’t any local aid.

Can Bad Glow Plug Symptoms Hinder an Engine Start?

No, not always. Even if one glow plug is malfunctioning, you can still start the car, but the performance of the whole thing will be much diminished.

However, if many glow plugs malfunction, the engine won’t have enough power to start. As a result, you may initially experience some starting problems, but under challenging circumstances, the car may not even turn on.

How Long Do Glow Plugs Take to Heat Up?

The glow plugs in your car need to warm up for roughly 15 seconds under typical driving conditions. This threshold might help you figure out whether there are any problems without glow plugs. If the car still hasn’t started after a few seconds or perhaps even minutes, you could need to consider glow plug problems.

Glow Plugs: Are They Only for Starting a Car?

What a wonderful question! The widespread notion that glow plugs are only used to start vehicles in cold weather is widespread. Glow plugs, however, are still helpful for the cycle and greatly lower emissions in the car, so that is untrue.

As a result, the duty of the glow plug does not finish when the car starts.

The Glow Plugs Vs.The Spark Plugs

Spark plugs and glow plugs both carry out the same functions as combustion engines, but they also have extra duties that are very distinct from one another. Other notable differences in their look include:

7. Onboard Diagnostics OBD handheld scanner
To rule out any more probable causes for the check engine light to come on, the glow plug must be changed. To do this, utilize an OBD 2 scanner, which can read any internal problem through codes and translate it into helpful information on the screen.

1. The Fuel

While spark plugs are found in gasoline-powered engines, glow plugs are used in diesel engines. Spark plugs in a gas engine produce sparks that light the mixture of gasoline and air in the ignition chamber. Glow plugs do the same function but in diesel-powered engines.

2. Difference In Heat

Given how flammable gasoline is, all it takes is one spark to ignite the vapors. Diesel, however, is less flammable than gasoline, hence the diesel engine requires greater cylinder compression and ignition temperatures. These levels can only be produced by diesel glow plugs, which then ignite the diesel and air combination in the engine’s combustion chamber.

3. The Durability

Because spark plugs operate continuously when a car is moving, glow plugs are more durable than spark plugs. Glow plugs, on the other hand, only work when there is combustion.

4. The Ignition Method

Spark plugs require electrical power to produce the sparks that ignite the mixture of gasoline and air inside the engine. To ignite the combination of air and fuel, glow plugs use electricity to warm up a heating element.

The end of the service life of diesel glow plugs will be indicated in a variety of ways. You need to contact a qualified mechanic right away if you discover any of these problems with your car. As an alternative, you may think about the DIY component that was discussed previously in this post.

Bad Glow Plug Symptoms: The Conclusion

Can bad glow plugs result in a power outage? Why am I supposed to be worried about malfunctioning light plugs? Owners of vehicles with diesel-powered engines frequently have these queries. You should be aware that glow plugs are effective in warming up the engine of the car and starting the ignition.

However, broken or bad glow plugs might reduce the heat supply, leading to more severe issues. However, you may watch out for the bad glow plug symptoms and discover great solutions to such problems.

One of the crucial parts of every engine that is in charge of heating the air-fuel combination and preparing it for combustion is the glow plug. Glow plugs can become damaged over time and need to be replaced, if not sooner, after about 100,000 miles.

Depending on the number of bad glow plugs, you may need to repair them right away or at the very least, you should not overlook the issue.

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