Samuel Gitukui on September 4, 2022 No Comments
Glow plugs are a component of diesel engines, they provide the engine with the necessary heat that is needed to ensure combustion takes place. In this post, we take a look at the cost to replace glow plugs, but first, we will find out more about this crucial component.
The glow plug will remain dormant if the diesel engine is warm and can start normally. When the temperatures drop and the diesel engine becomes cold, the glow plugs will help to get everything running again.
Glow Plug Light
Diesel engines are designed in a way that they need external help to get them to run. This is especially the case when living in extremely cold temperatures.
When you buy a diesel-powered vehicle, The glow plugs which are contained in the diesel engine will heat the air and fuel mixture allowing for combustion to take place. This will help the car’s engine to start efficiently.
The glow plugs, therefore, raise the temperatures in the combustion chambers which allow for an easier and more efficient detonation of the fuel-air mixture.
The driver, therefore, needs to wait a little while until the engine is warm enough before they can ignite and drive their car.
There are many different lights and symbols on the dashboard which inform the driver of possible problems with their vehicle. One of these is the “cold” light (aka the pre-glow warning light) which is also referred to as the glow plug light.
If you notice that the glow plug light has turned on, there are several reasons which could cause this. One of these is cold starts. There could also be malfunctions.
How The Glow Plug Works
The glow plugs will be activated when the driver puts in the ignition key and turns it on to the ON position. Remember that the engine needs to be cold for the glow plug to be activated. When the glow plugs get the charge for the car’s electrical system, they will turn the charge into thermal energy.
Glow plugs can be used in a similar way to BBQ coals. If say you were to throw lighter fluid on the coals this may not result in fire. However, if the coals have already been turned on, then they will ignite the fuel.
Whenever the glow plugs receive power, the tips of the glow plugs will turn a bright red or orange color thus turning hot. When the fuel starts to flow inside the combustion chamber it will be ignited.
When the fuel and the air mix are ignited, the engine will receive even more heat which will allow it to run smoothly without the help of the glow pugs.
Bad Glow Plug
When the glow plugs start to degrade and lose condition, you will notice that the engine starts to take longer to ignite. At worse the engine may not start at all.
This is when you need to look into the cost to replace glow plugs. Typically this will range from $230 to $290. This will be inclusive of labor costs with the glow plugs themselves costing between $90 and $110.
There is a higher chance of getting a diesel engine that has an external heater to start compared to a diesel engine that doesn’t come with an external heater.
You may also notice that the engine starts off running rough as the temperature continues to rise until it reaches optimum operating temperatures. This is often caused by a misfiring cylinder where one glow plug may not be working as expected.
Another way that you can tell that the glow plug isn’t working properly is if there is plenty of smoke that starts to come out of the exhaust. This is due to fuel getting inside the exhaust and then igniting.
You will also notice that there is a check engine light that has been turned on. Once the OBD system is checked, then this may show that there is an issue with the fuel delivery system. This could possibly be an indicator of damaged glow plugs.
Cost To Replace Glow Plugs, Symptoms #1 – Cold Starts
Let’s take a look at cold starts in more detail. First off diesel engines will not use spark plugs like the ones you’ll find in a Honda Civic, or most other common gasoline passenger cars. Often it is the heat caused by high-pressure compression which helps the engine ignite.
Diesel engines can be hard to generate enough high temperatures for the compression top start. To get over this problem the diesel engines will have glow plugs. They heat the air in the combustion chamber which could result in the coil light symbol in the dashboard turning on.
After the engine ignites then there is no more need for the glow plug.
So how long does the glow plug take to warm the cylinder? This time could vary based on the ambient temperatures as well as the car model. Often the average time can be anywhere from a couple of seconds to up to a minute to heat the combustion chamber.
After the combustion chamber is warm enough, the coil light should turn off. Now the driver can turn on the car and drive.
There are other starting aids in diesel engines such as an injection kit, coolant heater, block heater, oil pan heater, and air intake heater.
Cost To Replace Glow Plugs, Symptoms #2 – Blinking Glow Plug Light
If you notice that the cold light on the dashboard is blinking then this could show that there is a malfunction.
At this point, it is better to take the car to an auto mechanic and have the problem diagnosed and fixed.
The mechanic may find that the reason behind the blinking has to do with a faulty glow plug. It could be that the glow plug is unable to provide the required heat.
Another possible issue could do with a faulty timer which is unable to keep the glow plug running for the required amount of time. A managed or faulty timer could also result in damage to the glow plugs.
If there is a faulty glow plug, then this could manifest in the car in several ways. First off, you may find that there is a loss of power and that there is slow acceleration. There could also be misfiring or even a dropping in fuel economy.
You may want to take your vehicle and have it looked at by a qualified mechanic. The car technician will be able to identify the problem and fix it.
Cost To Replace Glow Plugs, Symptoms #3 – Glow Plug Warning Light
Should you drive with a glow plug warning light that has turned on?
Well, it depends on if the glow plug warning light is blinking or if it is constantly on. Often you may not be able to ignite your vehicle when the glow plug light has turned on. It is only after it has turned off that the car will usually ignite.
You can however drive when the glow plug light is blinking. That said, it is best to drive carefully and slowly to ensure you avoid overheating. You may also realize that your vehicle had dropped in performance. This is usually a safety mode.
A blinking glow plug light tells you that there is a potential problem. This is why it is important to ensure that your get the problem checked and fixed as soon as possible. This is also the case if you have a glowing light that turns on but will not turn off even while the engine has warmed up fully.
Spark Plug Vs Glow Plug
The combustion engine can either feature spark plugs or glow plugs. What is the difference between the two? It comes down to the type of engine. The spark plugs are a feature in gasoline while the glow plugs are a feature of the diesel engine.
Many people will wonder, why the difference between the gasoline engine and the diesel engine? What do the spark plugs do and what do glow plugs do? What are their respective roles in their respective engine types?
The Spark Plug
The spark plug is an important part of the gasoline engine. Such as the one you’ll find in a typical Subaru Forester or an Acura MDX. This type of engine simply cannot start without a spark plug.
The spark plug is in the cylinder head of the engine and connects to the ignition coil. The charge will go through the spark plug and jump the space at the end resulting in a spark. This ignites the fuel in the combustion chamber.
There are several types of spark plugs. These include copper, platinum as well as iridium spark plugs. They could also be classified as thread type or nut type depending on their sizes. Furthermore, they could be categorized as crush washers or tapers depending on their type of work.
The spark plugs work as long as the engine is running. They are always working to ensure the engine keeps working.
The fuel will mix with the air and then goes to the combustion chamber. Here the spark plug after getting a high voltage for the ignition coil will result in a spark plug igniting the fuel-air mixture. This happens thousands of times in a single minute.
The Glow Plugs
The diesel engines can start without the need of a glow plug if that is you live in a warm climate. Due to high temperatures in the air intake and low ignition temperature of the diesel.
This however may not be all that is needed to make sure that the injected fuel is properly ignited. This is because the temperatures may not be hot enough and could result in more emissions.
To get around this problem comes the glow plug. This is a device that is in each cylinder which allows for reliable starts regardless of the weather.
While the spark plug will work for as long as the car is running, this is not the case with the glow plug. The glow plug only works during the ignition process of the diesel car.
It does this by electrifying the heating elements allowing them to warm up which results in it emitting visible light. This is why it’s called a glow plug.
At this point, fuel will be sprayed on the hot glowing tip by the fuel injector while injecting the fuel.
This fuel will mix up with the air and will then evaporate and start the combustion process. This will happen even while the engine hasn’t warmed up yet.
Glow Plugs Test
There are several ways in which you can test if the glow plus is working. One of the most common ways is through the use of a multimeter.
Cost To Replace Glow Plugs, Testing – Method 1
Step 1: Get A Multimeter
This is a box that contains electronic circuitry to test out the electrical devices and electrical wiring. The multimeter features a dial that is in the middle whereby you can adjust the settings.
The multimeter has positive red as well as negative black leads for testing out the current and the resistance. The leads are greater metal clamps at the tips.
The multimeter often seems hard to use since it has many numbers but it is simple to use for this task as you only need to use a single setting.
Note that the analog multimeter could apply a just higher voltage on the circuit compared to the digital multimeters. This is why it is advisable to use the multimeters with care.
Secondly, keep in mind that the first digital multimeter reading is often not accurate. This is because there is a good chance that the current will fluctuate. The digital meters will sometimes have a hard time testing current that changes constantly.
On the other hand, the analog multimeters will feature a changing display, you will be able to see the fluctuations in the current. That said the analog multimeters aren’t as accurate as the digital multimeters. This is why you will be better off using the digital multimeter to test out the glow plugs. This will provide you with the true number of the resist.
The analog multimeter will prove much harder to read since it will list down all the possible results.
If however, you choose to make use of the analog multimeter ensure that you are using a multimeter that has a sensitivity of 20k Ohm/V.
Step 2: Set To Ohms
You will see the ohms settings denoted using shapes that look like a horseshoe that is upside down. There will also be a couple of vertical lines that contain the range of the ohms.
Step 3: Get A Resistance Value For The Multimeter
Take the two leads and cross them one over the other. Ensure that the metal clamps touch each other.
When using a digital multimeter, this will result in reading on the screen.
You will then need to take this number and subtract it from the reading of the glow plug.
Step 4: Test The Battery Voltage
You will need to change the setting of the multimeter to DC. Take the negative lead of the multimeter and place it on the negative battery terminal then take the positive battery lead and place this not the positive battery terminal.
The reading which you get needs to be close to 12.5 volts if, that is, the car is off. If the engine is running then the voltage should be around 13 volts.
In case this isn’t the matter, go to your vehicle’s battery and check it. You may also want to check the car’s alternator before you can continue.
The glow plugs are also less likely to work the right way if they lack the right voltage getting to them.
Step 5: Find The Glow Plugs
Go to the shop manual of the car and see where the glow plugs are located inside the engine. This can vary depending on the model as well as the make of your car.
Step 6: Take Out The Connectors From The Glow Plugs
You will normally find a cap that is set over the glow plugs. You will need to remove this cap to be able to apply the clamps of the multimeter on the glow plugs.
Take a look at the connector as well as the pins for signs of corrosion, rust, or even loose fittings. No, it’s a good time to clean them.
Step 7: Connect The Multimeter
Clip the multimeter’s negative lead onto any ground point on the engine.
The two main ground points are if you follow the wire that comes from the negative terminal of the battery onto the wall of the engine.
You can also follow the wire that comes from the alternator and also goes to the engine wall.
These two wires will connect to bolts. Connect the negative lead to any of these bolts to allow for grounding.
If you are not sure how to do this you can view your car’s owner’s manual which will help you find these ground points.
Step 8: Connect The Multimeters Positive Lead To The Grow Plug Top
If the negative lead of the multimeter connects to the negative terminal of the battery, then you need to leave it here.
Step 9: Multimeter Reading Evaluation
This step requires you to check the shop manual for you to get the best specs for your car.
Take the multimeter resistance value and subtract it from the glow plug resistance value.
Step 10: Replacing The Glow Plug
If you find that just one of the glow plugs is faulty, you will need to find the cost to replace glow plugs and replace all of them. It is not advisable to replace just one plug. If you find that the area around the glow plug is dirty you should clean the area first.
Some manufacturers will sell special tools that will reach into the bore of the glow plugs to help clean them first before you can install new glow plugs.
The tools work by scraping out and cleaning the carbon build-up. Some tools help preheat the chamber before you can add in the new glow plugs. Furthermore, these tools will also help to clean the carbon build-up on the threads which hold the glow plugs. This tool is called a reamer.
Cost To Replace Glow Plugs, Testing – Method 2
The above method is just one of the ways that you can test the glow lug using a multimeter. Let’s now take a look at a second method.
Step 1:
Start by removing the glow plugs from the engine. You can check the car owner’s manual to know where you can locate the glow plugs as well as how you can remove them.
This will depend on the make and model of your vehicle.
Step 2:
Set the multimeter to ohms.
Start by using the lowest ohms setting. If you find that the glow plug measurement is too high then this is a good sign of a faulty glow plug.
Step 3:
Now it’s time to find out the multimeter resistance value.
Take the two multimeter leads and cross them over each other. Take a record of the result.
Now take this reading and subtract it from the reading of the glow plug.
Step 4:
Take the negative lead of the multimeter and place it on the glow plug nut. You mustn’t place the negative led above the glow plug.
Step 5:
Take the positive lead of the glow plug and place it onto the tip of the glow plug. Whenever you take off the glow plug cap you will expose the glow plug tip.
Step 6:
Check the multimeter and read the results. Read the resistance value and subtract it from the resistance value of the glow plug.
Note that the glow plugs from the engine should have pretty similar readings. If you have a glow plug that has a higher resistance than the rest then this will affect the engine performance.
Step 7:
Now you will need to find the cost to replace glow plugs. In case you find a faulty glow plug it is good practice to replace the glow plug. Always avoid replacing a single glow plug but instead replace all the glow plugs.
Frequently Asked Questions
How Many Spark Plugs Does A Diesel Have
Diesel engines don’t use spark plugs. Instead, they have glow plugs. There will be a single glow plug per cylinder. This then means that a 6-cylinder engine will have 6 glow plugs while a 4-cylinder engine will have 4 glow plugs.
Do Diesels Have Spark Plugs
No, diesel engines do not use spark plugs instead they use glow plugs which increase the temperatures inside the cylinder to allow for efficient combustion to take place.
What Do Glow Plugs Do
The glow plugs are heating elements that are used to raise the temperatures in the cylinders. This helps to encourage efficient combustion of fuels allowing you to drive.
