Step-by-step instructions for changing the glow plugs!

Reading time 10 Min.

Recently updated on September 22, 2023 at 09:02 am

[Update: 22.09.2023] This post was updatedto take more recent information into account. The fear of changing the glow plugs (also known as glow plugs or glow plug) is known to many diesel drivers. If you look on the Internet, you will find countless stories that have the potential to Panik trigger. It's about torn off glow plugs and in the end the entire cylinder head has to be repaired for a lot of money. You only need a few Assembly and disassembly instructions must be observed and half the engine damage does not occur. The following text is intended to take away the fear of changing glow plugs!

Change pre-glow plugs!

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1. What is the task of the glow plugs?
2. How is a defective glow plug noticeable?
3. Signs of a defective glow plug.
4. Check glow plugs with a diagnostic tool.
5. Check glow plugs manually.
6. What if the measurement shows no error?
7. Are defective glow plugs dangerous?
8. Step-by-step instructions: Replacing the glow plugs
9. What if a glow plug doesn't come off?
10. What to do with the old glow plugs?
11. FAQ about glow plugs.

What is the task of the glow plugs?

A diesel engine needs the glow plugs for a cold start. A gasoline engine needs the spark plug to ignite the fuel-air mixture. Diesel does not have to be ignited in this way, however. The glow plugs use a filament to heat the combustion chamber and, in older models, also the antechamber. They work with temperatures of up to 1.300 ° C. The diesel needs this operating temperature so that it can self-ignite. However, during a cold start, the high operating temperature required for self-ignition is missing.

However, once the operating temperature has been reached, the heat from the engine block and the heat generated by the compression of the mixture are sufficient for self-ignition. Incidentally, a modern diesel engine can use the glow plugs to reduce exhaust gases and noise emissions during the warm-up phase to reduce. Modern glow plugs are still glowing up to three minutes after. For this purpose, some glow plugs have their own sensors for detecting the pressure in the combustion chamber. "Back to overview

How is a defective glow plug noticeable?

Have glow plugs no prescribed replacement interval and are only replaced when they are broken. It doesn't hurt the glow plugs though every 60.000 km to replace. In modern vehicles, the glow plugs are one of the components relevant to exhaust emissions and they are monitored using the engine management system. If the control unit detects a fault in the glow plugs, the Engine control lamp (MKL or MIL) triggered. But this does not necessarily have to be the case.

For example: a modern six-cylinder with six glow plugs usually starts without any problems even with five. In this case, the MKL was mostly glowing not on.

There is a possibility one Diagnostic test to make who betrays which glow plug is defective. It may then be sufficient to just replace this one glow plug. However, the exchange is recommended of all candles. If the defective glow plug actually triggers the engine control lamp, then with some manufacturers this leads to the vehicle being in the Emergency run goes. In emergency mode, the vehicle can only continue its journey slowly, at a low speed and with a considerable increase in fuel consumption. "Back to overview

Signs of a defective glow plug.

• The vehicle smokes black when starting.
• Several start attempts are required.
• The engine has a strong smell after starting.
• The engine nails harder than usual in the starting phase.
• It takes a long time to start and places a heavy load on the battery.
• The control lamp of the glow plug system lights up / flashes.
• Fault memory entry (e.g. glow plug cylinder X defective)

Often it is only noticeable in the cold season that the glow plugs are no longer working perfectly. If it's colder outside, the starting difficulties and the engine shudder after starting are more noticeable than in summer. "Back to overview

Check glow plugs with a diagnostic tool.

For this it needs a OBD-compatible diagnostic device (EOBD), which can be connected to a suitable app on a smartphone. These diagnostic devices are inexpensive and easy to use for the layperson. The glow plugs can also be used manually Multimeter to be checked. "Back to overview

Check glow plugs manually.

First, you need a simple multimeter, which you can get at most hardware stores. Then the following steps are carried out:

1. The vehicle in front of the Roll away to back up.
2. Turn off the engine and the hood öffnen.
3. Exposing the glow plugs:
   - the engine cover is often just plugged in and can be pulled off upwards. Some models have a manual that tells you where exactly the glow plugs are. There are also countless videos on the net for almost all models.
4. Expose glow plugs.
   - Most glow plugs have a 1-pin connector that can be easily pulled out. The engine block serves as a ground or negative pole.
5. Multimeter to the smallest measuring range set for the resistance, i.e. set in ohms. Inexpensive multimeters often show 200 ohms.
6. Measure all glow plugs.
   - In order to measure the candle, a measuring tip must be held against the engine block. The other measuring tip comes to the contact of the glow plug. This contact is the thread on the tip of the glow plug. The resistance lies between 0 and 1 ohm the measured glow plug is OK. If a glow plug is not working properly, in most cases the resistance is so high that it can no longer be measured.

Since the vehicles usually have several cylinders and thus several glow plugs, it makes sense to compare the results with one another. In this way, conclusions can be drawn about the functionality of the individual glow plugs. The resistance measurements can only be carried out when the plugs are removed, otherwise other electronic components may be damaged. "Back to overview

What if the measurement shows no error?

Then you should check whether the glow plugs are at all Get tension. To do this, the multimeter should be set to 20 volts. Now will from the connector to the engine block measured. But the plugs of all glow plugs are still there deducted. Since tension has to be built up briefly, a second person should briefly switch on the ignition. The result should be around 12 V or -12 V, depending on how the multimeter is connected. Important note: It is possible that the engine control lamp has not come on at this point in time. If this is the case, then the supply voltage should not be measured, because this measurement will trigger the engine control lamp with a high degree of probability. "Back to overview

Are defective glow plugs dangerous?

Everything starts with a difficult start, what first no danger triggers for life and limb. The jerking, the possible loss of performance and the poor starting behavior can, however, result in additional costs for the vehicle. Due to the difficult starts, the Starter and the Battery damage. All components that come with the exhaust aftertreatment have to do can also be damaged in the long run. These components include the Catalyst, Rußpartikelfilter or AGR valve. It could happen that these parts become clogged with soot and subsequently have to be replaced or laboriously cleaned. Under an increased soot load can also Outlet and inlet valves, the Lambda sensors or the turbocharger Suffer. And an increased thermal load is also one of the consequences. "Back to overview

Instructions: Replacing the glow plugs

• Requirement: Considered difficult.
• No special tools are required.
• Whether a lifting platform or a pit is necessary depends on the vehicle.

Let's go:

1. The vehicle set a link from your homepage to Fewo-von-Privat.de Warmed up and on Operating temperature .
2. The vehicle in front of the Roll away to back up.
3. The engine turn off and the hood öffnen. Attention: Parts of the engine are warm to hot. There is a risk of burns.
4. By checking the glow plugs in advance, the position of the glow plugs is known.
5. Expose glow plugs.
6. Unplug the glow plug connector.
7. Spray glow plugs with injector and glow plug remover.
   - the spray should work for about 10 minutes. It ensures that the candle cools down a bit and thus contracts slightly. This allows the penetrating oil to penetrate deeper into the thread.
8. Important: Glow plugs have a tightening torque and a breaking torque that should be specified by the manufacturer. Hence, glow plugs should be used only with one torque wrench installed and removed will. This prevents it from breaking off if the glow plug is still too tight.
9. You can now carefully try to loosen and remove the glow plugs with a torque wrench. (Torques between 20 and 40 Nm when unscrewing)
10. After removal, the glow plug should be drilled with a corresponding one reamer getting cleaned. However, the reamer should be greased with silicone-free grease so that residues are transported to the outside and don't fall into the engine. The awl is inserted into the candle shaft and tightened. Make sure that no other dirt gets into the cylinder through the open candle shaft.
11. The new glow plugs should come with Glow plug assembly grease be greased on the shaft and thread. This grease facilitates assembly and later disassembly.
12. The new glow plugs manual screw carefully into the cylinder head.
13. Now with that torque wrench Tighten according to the manufacturer's instructions.
14. Plug again put on and what you dismantled (engine cover, etc.), again plant.
15. Any entries relating to the glow plugs in the fault memory Clear.
16. Carry out a test drive and read out the fault memory again. "Back to overview

What if a glow plug doesn't come loose?

If a glow plug cannot be persuaded to leave its original place, everything should be reassembled and the whole thing should be repeated the next day. If that doesn't work either, you can try again a day later. You should always do the Steps 1 through 9 go through. If this does not lead to success, it is advisable to go to the workshop. "Back to overview

What to do with the old glow plugs?

Old glow plugs belong not in the household rubbish. In Germany it is regulated in such a way that manufacturers of electronic and electrical devices normally use the old parts have to take back. However, this does not apply to spare parts. Even recycling centers do not accept defective car parts. Then there is still the way to Scrap dealer or to do Car reclaimer. But you won't get any money for it, but you can be happy if you can give it away for free. However, if you regularly have scrap metal, you can of course collect it until the quantity can be sold. "Back to overview

FAQ about glow plugs:

• Which glow plugs can be bought?
  You are on the safe side with well-known manufacturers such as BERU, Bosch, Denso or NGK.
• Can I continue driving with defective glow plugs?
  Basically yes. However, modern vehicles can throttle the engine and you can only drive slowly. In addition, various parts in the exhaust gas area can suffer. In addition, a defective glow plug can in the worst case melt away and damage the combustion chamber / cylinder head.
• Do I have to dismantle the cylinder head if a glow plug breaks off?
  No, there are special tools for this case. These tools can remove the glow plug even if it is torn off, without having to remove the cylinder head. This can be used to repair the thread in the cylinder head in the assembled state.
• Do I need a new cylinder head if the glow plug breaks off?
  Basically no, there are tools that can save the situation without the need for a new cylinder head.
• What does it cost to change the glow plug in the workshop?
  The costs depend on the number of glow plugs and the vehicle model. If the vehicle has a four-cylinder, the price in an independent workshop can be between 100 and 300 euros.
• What is the replacement interval of glow plugs?
  There are no solid Change interval. Like a clutch or gear oil, glow plugs should last the life of a car. However, there are recommendations that glow plugs, like the spark plugs to change every 60.000 km.
• General inspection despite defective glow plugs?
  If an error message is saved in the control unit because of the defect, this can, depending on the exact nature of the error and the interpretation of the inspector, lead to the general inspection not being passed. If the MKL lights up, the badge will definitely be refused. "Back to overview

Changing glow plugs – useful information and costs

When it comes to diesel engine maintenance, glow plugs play a crucial role. They are responsible for pre-heating the engine and ensuring that the diesel fuel is ignited properly. But when should you replace them and what are the costs? How much does it cost to change 4 glow plugs? Depending on the vehicle and workshop, the costs for changing four glow plugs range between 150 and 250 euros. This includes both the costs for the glow plugs themselves and the working time.

Glow plugs – function, defects and consequential damage

A defect in one or more glow plugs can occur unclean combustion and lead to increased pollutant emissions. This leads to a poorer environmental balance and increased fuel consumption. In cold weather, a vehicle with defective glow plugs may have difficulty starting. For those who are considering changing the glow plugs themselves: It is doable, however special tools required and a certain level of specialist knowledge is advisable. Therefore, many recommend changing it in a specialist workshop. By the way, driving with defective glow plugs is possible, but it can lead to damage to the starter, battery and exhaust aftertreatment systems.

identification mark Faulty glow plugs can include a reluctance to start engine, a grinding combustion noise, and blue/white smoke. The life of a glow plug can vary. Some can already do so 50.000 kilometers lose their function, while others up to 150.000 hold. For broken glow plugs, removal can be complicated and expensive, with costs ranging between 1200 and 1600 EUR can lie if the motor needs to be opened for access.

It is checked with an ohmmeter!

The best way to check the condition of a glow plug is to use one ohmmeter. If the glow plugs are defective, the measuring device shows infinite resistance. For those thinking about brand quality: NGK, Beru and Bosch are considered the best brands in the glow plug sector.

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