How do you test glow plugs

Detect and replace defective glow plugs in diesel

The glow plugs, sometimes called glow plugs, are found in cars with diesel engines in place of the spark plugs. However, they take on a completely different function. In this guide we reveal how you can recognize defective glow plugs in the car, what symptoms they are causing and how you can change the glow plugs yourself.

Function of the glow plugs in diesel

Your car is equipped with glow plugs if you have one diesel drive. They sit in the same place as the spark plugs on a gasoline engine. In contrast to the spark plugs, however, the Glow plugs not used with diesel while driving. you are just for start important. The Diesel mixture ignites by itself when the engine is running and explodes under the high pressure in the combustion chamber.

However, this process sets a certain level Base temperature ahead. Glow plugs are used to Combustion chamber of the cylinder during a cold start to preheat something, which is where the technical term "preheating" comes from. Each cylinder contains a glow plug, the structure of which is nothing more than a small electrical heater. The Preheating lasts for most cars just a few seconds and is indicated by a symbol in the form of a twisted wire.

Lifespan of glow plugs

As with many other parts on the car, the life of the glow plugs depends very much on the Use of the car from. As mentioned above, the glow plugs are used when the car is started. This means: The more often you start the car, the faster the heating elements wear out and the sooner the change is necessary. The glow plugs can already be used on frequently started cars 50,000 km fail their service. It can also be used for long-haul cars up to 150,000 km take until the change is necessary.

Glow plugs in the car are off Metal or ceramic. That depends primarily on which car you drive. Newer cars are often with Ceramic glow plugs equipped that higher temperatures tolerate and that Accelerate preheating. When changing, the exact type of candle that was installed at the factory should always be installed.

Signs of defective glow plugs in the car

In the event of a total failure, the case is clear: the car can no longer be started, changing is inevitable. More often, however, it happens that individual glow plugs insidiously refuse to work. The signs also appear gradually. In the event of a failure, whether acute or insidious, you should in any case act quickly and defective candles because otherwise you will no longer be able to implement step 2 of our guide.

A common symptom is a Restless and jerky start of the engine. This is because the cylinder with the defective candle does not ignite and is "dragged along" by the other cylinders. When it is warm, the ignition starts and the engine runs smoothly again. By exchanging the candles, the error will be rectified immediately.

A Failed pre-glow fuse often announces a defective glow plug. After changing the fuse, check the candles. Also one extended preheating time can herald the creeping defect of the glow plugs.

Unusual smoke development after the start can also be caused by defective glow plugs. This is because the exhaust system works most efficiently at operating temperature. Due to the defective plug, the engine starts cold and takes longer to get up to temperature. In this case, changing the plugs prevents deposits from soot and other pollutants and increases the service life of the entire exhaust system.

Fast functional testing of glow plugs with a multimeter

The glow plugs are electrical heating elements, so be sure to replace them with one electrical measurement with a multimeter possible. To do this, follow the one shown procedure:

  • Remove the contact from the glow plugs
  • Set multimeter to resistance measurement (Ω)
  • Place a measuring tip on the mass on the car (e.g. a screw)
  • Hold the other measuring tip at the tip of the individual glow plugs

The multimeter should have one for every glow plug the lowest possible resistance show, mostly at about 1 Ω lies. Most measuring devices also emit a beep. Compare the resistance values ​​of all candles, because the defective one is clearly out of line. Is the Resistance significantly greater, so z. B. 5 Ω, 10 Ω or even infinite, then the diagnosis is complete: The Glow plug is broken and should be changed according to our instructions.

Exchanging the measuring tips usually has no effect, as the candles can be measured in both directions. But be careful: It is important to disconnect the glow plugs beforehand, otherwise the measurement is not meaningful!

Guide - change glow plugs yourself

Repairing broken glow plugs in the car does not make sense due to the price of the new parts. In addition, there are usually no individual parts at all, only complete candles to swap. Also, you should note that you Glow plugs never individually, but always change as a complete set. Our guide tells you how to change yourself.

To replace the glow plugs, you need the following first equipment:

  • Glow plug set
  • Torque wrench with attachments
  • Penetrating oil, silicone-free grease
  • Special reamer
  • Brush or soft brush
  • Warmth and patience

1. Preparation and dismantling of the old glow plugs

Caution, as work is being carried out on the electrical system: Before starting, the negative pole of the battery is disconnected!

The first step in replacing glow plugs is to dismantle the old plugs. Often this is also the case biggest challenge when changing. Due to the long operating time and the large temperature differences, these become incredibly solid. Under no circumstances may you use a force above that specified Breaking torque work because the Candles can tear off! Then a professional has to drill out the glow plugs, which causes additional costs.

First the electrical connector removed. Then the Remove dirt from candles and the area around them. Due to the narrow engine compartment, a paintbrush or a soft brush is ideal here to better reach the corners. Now try connecting the glow plugs with that torque wrench set to the breaking torque to solve. In most cases this won't work because the outside threads of the candles are too tight. If the candles can be unscrewed directly, you can continue with changing from step 3. If the plugs cannot be loosened with the breaking torque, continue with step 2.

2. Loosen the fixed glow plugs

Now comes a Oil with creeping properties for use, often referred to as rust remover in the trade. Plenty of it may be applied to the thread of the stuck glow plugs. The penetrating oil slowly works its way into even the smallest of gaps. It is best to leave it on overnight and try changing the candles again the next day.

Temperature changes favor the process. The easiest way to warm up the engine is while driving. This means that the car can run and be driven quietly. By alternating between hot and cold, the material works and creates gaps for the penetrating oil. Spray some oil several times a day, as it evaporates quickly on the surface.

A regular test with the torque wrench provides information as to whether the glow plugs are already loosening and ready to be changed. Caution: you may never exceed the breaking torque of the candles, which is usually between 20 and 45 Nm, depending on the size. As soon as the threads move, changing the glow plugs can continue with step 3.

3. Remove glow plugs and clean shaft

Changing the glow plugs on the car can be done as soon as they come loose. Unscrew the glow plugs and when removing it, be careful not to let dirt fall through the opening. Therefore, a rough cleaning was carried out in the first step.

Now have to Glow plug shaft and thread cleaned become. This is the easiest and most reliable way to do this with a special reamer. This is available for every candle size and is simply screwed into the opening instead of the candle as far as possible. With a little silicone-free grease, the reamer glides more smoothly and picks up residues and soot. Then the reamer is unscrewed, cleaned, re-greased and screwed into the next shaft. In this way, all shafts are reliably cleaned within a few minutes.

4. Replace glow plugs and install according to regulations

Before changing, you should check whether the new Glow plugs ordered correctly were. They have to look just like the old glow sticks. Especially that Thread on the shaft the candles and the Connection on the back have to identical be. Insert the candles by hand and check whether they can be screwed in without resistance.

After changing the candles, these are still provided with the Tightening torque screwed tight. Make sure that the tightening torque is well below the breaking torque from step 1. The glow plug documents contain information on the correct torque, which is usually between 10 and 30 Nm, depending on the size of the plugs.

Now there will be electrical connector connected. As a final test, it is now tried out whether the glow plugs are working and that Start the car leaves.

Change glow plugs yourself - what are the costs?

If the glow plugs are defective, you have the option of changing them yourself or having them replaced in a workshop. The do it Yourself is of course cheaper, but the workshop incurs higher costs.

Fall for changing glow plugs depending on the model Costs between 10 and 25 € per candle at. The Reamer to clean the shafts costs depending on the model between 15 and 40 €. This results in total costs of an average of 80 to 100 €.

Have glow plugs changed in the workshop

The Changing in the workshop is easy. You drop off your car and pick it up when everything is ready. During this time, experts replace the glow plugs. The workers are familiar with the required work steps and torques. Even with that Drilling out jammed candles the workshop has experience and does this work reliably.

In addition to the Price of glow plugs even those working hours pay. Normally a workload of 1 - 2 hours is required, with particularly firm candles even more. At typical hourly rates, the Working hours between € 50 and € 200 added to the price of the glow plugs.

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