Are there spark plugs on a diesel engine? There are, but they, unlike those installed on a gasoline engine, play a slightly different role. Glow plugs for a Mercedes, BMW, Nissan, Volkswagen or Hyundai diesel engine help start the power unit and warm it up, which is especially important in the cold season. That is, these elements protect the motor from excessive loads. And one more function - facilitating good atomization fuel.
The service life of glow plugs is solid - up to 100 thousand kilometers (this is more than one year of operation). But the resource may be less: it all depends on the operating conditions vehicle, driving style, as well as manufacturer. Read more about when glow plugs should be replaced, what kind of design they have, and how to determine their malfunction.
Device
Outwardly, they are similar to those installed in a gasoline engine, but the design is somewhat more complicated. Glow plugs do not produce a spark; they are based on a heating element in the form of a spiral, which can be metal or enclosed in a ceramic “case”. In the first case, we are talking about two “curls”, one of which serves for heating, the second protects against overheating. The next type of product is a spiral placed in a ceramic shell, due to which heating occurs faster. The tip of the candle heats up to 1350 degrees. The design also includes an incandescent filament consisting of a pair of resistors. The first of them has a constant resistance. The second one has an adjustable temperature coefficient. That is, when the engine temperature changes, the heating of the starting elements also changes. This allows you to save energy.
Ceramic products are considered more promising: such spark plugs not only quickly heat up the tip, which allows you to easily start a diesel power unit at low temperatures, they also have other advantages: these spare parts are suitable for Euro 5 and 6 standards. This is due to the fact that the products with a ceramic shell guarantee an intermediate glow mode. This optimizes the process of restoring the filter, which is “engaged” in reducing the soot content in the exhaust of Sang Yong Aktion, Kyron or other similar cars.
Control
The operation of glow plugs is controlled by the ECU, a separate unit or a special relay. Their work is related to data received from sensors that determine the crankshaft speed and coolant temperature. Many car models have a function to maintain heat after starting to reduce the noise level from cold engine(Land Rover Freelanders, and not only them, are guilty of this). When are glow plugs replaced and why do they fail?
Signs of malfunctions and their causes
It is best to identify the problem during the cold season. If one part is faulty, the diesel engine will have difficulty starting and will be extremely unstable. If two or more elements are inoperative, the engine may not start at all. The second sign is thick White smoke from exhaust pipe. If both symptoms are present, all glow plugs must be checked. The reasons for their malfunction may be:
- resource development;
- problems with the spiral: poor heating, short circuit with the rod or its rupture (burnout) - the latter malfunction is associated with an excessively high temperature of the gases, which is due to large deposits on the cylinder walls;
- violation of the integrity of electrical wiring;
- breakdown of control equipment: untimely injection or insufficient injection pressure.
There is only one solution to the problem: replace the parts.
How to detect a fault
Weak heating of the coil is detected by its heating time, which should be no more than 50 seconds. To make sure that the incandescent element is working properly, unscrew it and connect the central contact to the battery positive and the housing to the negative. If heating is normal and occurs in less than a minute, then the problem is faulty electrical wiring or bad contact. How else can you check the serviceability of the starting elements? diesel engine without twisting? Prepare your multimeter and switch it to resistance measurement mode. Disconnect the central wire from the contact and touch it with the positive probe (minus - on the body). If the instrument needle does not move, the part is faulty.
In the majority modern cars there is a self-diagnosis system: if even one spark plug is faulty, the corresponding indicator on the dashboard.
Replacing glow plugs yourself
Initially, it is worth noting that it is recommended to replace all products at once, even if only one is faulty. The glow elements are located in the upper part of the cylinder head near diesel injectors. Sometimes candles are covered with a plastic lid on top, protecting them from dust and dirt. The protection will have to be removed.
Preparatory work
First you need to remove the terminals from battery. Next, remove the tips attached to the contacts glow plugs using nuts. Move the explosives themselves a little to the side so that they do not interfere with the removal of the glow plug.
Unscrewing the spark plug
This must be done with care to avoid damaging the threads inside the cylinder head. Use a socket ratchet. There is also a risk of breaking the part itself, which can lead to serious work on drilling out the fragment and removing it.
Important point: among experienced craftsmen There is no consensus on which diesel engine is better to turn out the spark plugs: cold or warm. On the one hand, there is a risk of getting burned, but on the other hand, it is much easier to unscrew a spark plug from a hot engine: as is known from physics, when heated, bodies expand. This is especially true if glow plugs for a long time did not get out or the car sat idle for a long time.
Cleaning the spark plug holes
First remove dirt from spark plug holes. This procedure It is recommended to use a special reamer to clean the holes with maximum efficiency. Apply lubricant to the fixture before screwing. After completing the procedure, blow out the holes compressed air. Also, do not forget to clean the contacts on each spark plug and high-voltage wire.
Installation
If the spark plugs you decide to change are not new, first make sure they are working using one of the above methods. You need to tighten the parts until resistance appears: the tightening torque is best adjusted torque wrench– the value is 15 Nm. Do not allow it to be overtightened - subsequent unscrewing poses the risk of breaking the spark plug.
Once the spark plugs are properly screwed into place, tighten high voltage wires: It is advisable to also clean the nuts with sandpaper. Next, install the protection and start the car: smooth engine operation indicates normal operation glow candles. If this is not the case, you will have to diagnose the diesel engine to determine the functionality of the electronic control units and the integrity of the electrical wiring. The process of replacing glow plugs even for inexperienced driver on " Peugeot Boxer", "Ford Transit" or another similar car will take no more than half an hour (see video).
Results
Timely replacement glow plugs allows not only to ensure normal diesel starting and the same operation. Faulty spark plugs force the starter to turn the crankshaft for a long time. And this often ends premature exit it is out of order. The price is incomparably higher than glow plugs: so it is economically profitable to monitor their “health”.
These small devices they heat the air in the combustion chambers even before the diesel engine is started. These parts increase the resource of the unit, saving it from enormous loads in cold weather.
Second roles
After starting and warming up power unit, spark plugs take on a secondary role - they help atomize the fuel. The fuel entering the combustion chamber using a nozzle collides with the spark plugs. Creates a swirl effect. This improves the formation of the mixture.
Device and types
The shape of the part is similar to those used in gasoline engines. But glow plugs do not produce sparks.
The candle is based on a heating element - a metal or ceramic spiral. One such part can heat up to a temperature of 1350° in less than a second.
Metal heater
The metal heating element consists of two spirals. One is heating, the second is adjusting. The first function is maximum quick heating tip. The second protects the part from severe overheating. This is possible because as the temperature increases, the resistance on the adjusting spiral increases.
The free space between the heating tube and the two spirals is filled with an insulator. It also performs several tasks - it protects the spiral from various mechanical damage and transfers heat efficiently. A candle with a metal part can heat up to 1000°.
Ceramic heater
This design is similar to metal in its operating principle.
Its design feature is that the spiral is enclosed in a ceramic shell. Because of this, such an element will heat up faster. The power of this candle is also higher.
Principle of operation
So, the heating element is located on the cylinders of the power unit, where turbulence occurs fuel mixture. When the driver turns the key in the lock, voltage is applied to the spark plug and it heats up very quickly. This can be seen from the indicator on the dashboard.
It should take about 5 seconds for the candle to fully start.
Then it becomes completely heated and warms up the combustion chambers of the unit, as well as the air entering them. But these seconds are only enough for the candle to self-heat. To heat the air and cold parts of the cylinder block, as well as its head, the capabilities of this part are not enough.
So, main function- heat the fuel to such temperatures at which it can easily evaporate and ignite through compression.
Control system
Controls the operation of the relay or ECU or a separate unit. The electronic unit can supply different voltages to the spark plug and also control the temperature. The operation of the electronics and relays is influenced by coolant temperature sensors, as well as crankshaft speed sensors.
IN modern diesel engines Spark plugs, in addition to preheating, provide additional heat after startup. This function allows you to significantly reduce the noise level when the fuel is burning in a cold unit.
Malfunctions and their symptoms
Spark plugs, like any other parts, fail. This can be determined by weak heating of the spiral, short circuit of the core to ground, short circuit between the core and the central rod, burnout or rupture of the spiral.
In many cases, incandescence is required
Weak heating can be detected by the level of heating of the control element spiral. The coil on such an element should completely warm up in 50 seconds. If the battery is in good condition, then the cause of the malfunction may be poor contact.
If the core is shorted to ground, this will lead to overheating and then burnout of the control elements, additional resistances, or spark plugs that are located between the non-working and control elements. Also, due to a malfunction, elements located behind the problematic part may turn off. Therefore, it is very important to know how to check the glow plugs and how to then replace them if necessary.
Typical causes of malfunctions
A common and popular malfunction is burnout of the spiral. This problem can be detected by the fact that the control element does not heat up. If you close the spark plug terminals with a metal conductor, you can see sparking.
In this case, it is necessary to replace the glow plugs on diesel cars.
Often, a malfunction such as burnout can occur due to high filament currents or too high gas temperatures, which is caused by a large amount of carbon deposits on the cylinder walls. The spiral is destroyed especially quickly due to corrosion.
Breaks in the heating coil are the consequences of problems in the power system. This is due to untimely injection, too low injection pressure, as well as other faults. In this case, inspection and repair of diesel engines is already necessary.
Checking the spark plugs
At warm weather Outside the window, the failure of filament elements is almost invisible. Another thing is winter. There are two verification methods. Each of them requires tools, skills, devices.
How to check glow plugs: method No. 1
An insulated wire is required for testing. Then the candle is turned over so that the heater is at the top. The central electrode is installed on the “+” of the battery. A wire connects the negative terminal and the spark plug body. If the element heats up quickly, then this part is serviceable. There is no glow or only the tip becomes hot - the glow plugs on diesel cars need to be replaced.
Method No. 2
Often there is neither the time nor the tools to remove elements from the cylinder head. So, a multimeter will help.
The device is put into resistance measurement mode. But before that, the wire to the central element is disconnected from the spark plug. Next, the plus of the multimeter is connected to the central electrode, the minus - to the side of the case. There is no indication - the glow plugs on diesel cars need to be replaced.
Replacement
To dismantle and then install a new spark plug on diesel units, must be applied special tool, this is a head for M10. In addition, installation should only be performed with a torque wrench.
Dismantling is carried out strictly in order. The first step is to find out where the glow plugs are located in specific engine. Then the wires are removed from them, and the well is cleaned with compressed air. Next, it is important to treat the element with lubricant or any other anti-stick agent. After this, a little oil is poured into the well. Then, using a special wrench, they unscrew the spark plugs - turn them smoothly, without sudden blows or loads. The place from which the part was dismantled is cleaned and installed new spark plug incandescence Its price depends on the manufacturer, but in any case it is small. For cars imported production it will range from 600 to 900 rubles at the current exchange rate.
Sometimes some problems may arise during the dismantling process. There is a situation when part of the product can be unscrewed, but the second remains stuck in the cylinder head. Sometimes even after dancing with tambourines around the problem, the element refuses to get out. You should not try to uproot the spark plug - it is better to go to a place where diesel engines are repaired.
In the engine internal combustion The spark plug is designed quite simply - the central electrode is covered with powerful ceramic insulation and is half inserted into a metal housing. Free “bottom” end central electrode has a contact for connecting the high-voltage wire of the ignition system. And the “upper” end protrudes slightly from the annular band of the ceramic insulator and approaches (with a small guaranteed gap) to the side contact of the metal body. To install the spark plug into the cylinder, the metal body has a threaded part and a hexagonal collar (for tightening the spark plug with a wrench).
The glow plug of a diesel engine is designed almost similarly - it only lacks a side electrode, and the central one is not intended to supply a spark, but to heat the air in the engine cylinder (for this purpose, there is a spiral inside the spark plug with high ohmic resistance).
Other names
The correct "academic" name for spark plugs is "spark spark plugs for gasoline engines" However, in common practice the term "spark plugs" or simply "plugs" is more often used. Do not confuse spark plugs in a gasoline engine with glow plugs in a diesel engine!
Purpose of candles
Spark plugs provide ignition of the compressed fuel-air mixture in the cylinder of a gasoline engine by a spark discharge. The working gap between the electrodes of the spark plug is about 0.7-1.5 mm and it is not difficult to “pierce” it with an electric discharge - but this is in air. But in a cylinder filled with a compressed (very dense) and practically non-conducting gasoline-air mixture, in order to produce a spark, a voltage of tens of thousands of volts must be applied to the electrodes of the spark plug! In addition to the spark source, spark plugs perform another important function– participate in heat removal from the combustion chamber. This ability is characterized by the glow number of the candle. The smaller it is, the hotter the spark plug is during operation.
For high-speed, highly accelerated passenger car engines, only “cold” spark plugs are used (with a heat rating of at least 17 - according to the Russian classification). If the spark plug cannot cope with heat removal, then under certain engine operating conditions the hot electrode can act as a source of glow ignition. That is, when the fuel-air mixture ignites not from a spark - at the strictly necessary moment, but ignites from contact with a hot insulator. Glow ignition disrupts the operating process of the engine (deteriorates power and efficiency) and can lead to serious defects in the piston group parts and valve mechanism.
In a gasoline engine, spark plugs are the source of ignition of the mixture, that is, one of the key components for ensuring the working process. But in a diesel engine, glow plugs serve only to initially heat the air in the cylinder - in order to facilitate engine starting at low ambient temperatures. After a successful start and some warming up of the engine, the glow plugs are turned off and do not participate in any way in the working process inside the cylinder.
Symptoms of a problem
In general, spark plugs are a fairly reliable engine element. However, the harshest working conditions ( heat, aggressive corrosive effects of hot gases, erosion of metal under stress, etc.) lead to the likelihood of defects. First of all, this concerns carbon deposits on the spark plug electrodes and an increase in the working gap between them. To a certain extent, these malfunctions can be eliminated (by cleaning from carbon deposits and bending the side electrode to restore the normal working gap). With further wear, the only option is to replace the spark plugs with new ones.
A faulty spark plug in a gasoline engine can be identified by the following symptoms (remember that this is indirect signs– their “culprit” can be not only candles!):
- Difficulty starting the engine (you have to keep the starter on for a long time);
- the engine “troits” (the “odd” sound of the engine is noticeable, increased vibrations on Idling and twitching when moving at low speed);
- drop in engine power;
- a significant increase in fuel consumption (as well as the concentration of carbon monoxide in exhaust gases);
- “sluggish” engine speed.
In all listed cases It will be useful to unscrew the spark plugs and visually assess their condition (are they heavily covered with carbon deposits, are there any visible “potholes” on the surface of the electrodes) and check the gap between the electrodes with a feeler gauge. If you restore " marketable condition“The candles are successful, you can try to use them for some more time. Otherwise, all that remains is to find out how much it costs to replace spark plugs at a good car service center!
A malfunction of diesel glow plugs manifests itself in difficulty starting the engine at low (less than +5 °C) ambient temperatures. If the battery is charged, the starter “vigorously” rotates the engine, and there is no sign of condensation in the fuel (that is, high-quality diesel fuel is used, which corresponds to the season and is well filtered during low temperature air), then difficulties with starting the engine are associated precisely with the failure of the glow plugs. You can check the performance of the spark plugs using an ammeter:
- the supply wire is removed from the spark plug and connected to one of the ammeter contacts;
- the second contact of the ammeter is connected directly to the glow plug terminal (since the current is determined, the ammeter - as it should be - is connected in series to the open circuit);
- the ignition is turned on - the engine control unit must immediately activate the spark plugs, that is, supply current to them;
- The ammeter readings are read - if the current value of a particular spark plug is below 12 A, it is faulty.
You can also check the spark plugs using a multimeter - if their passive resistance is more than 5 ohms, then the heating coil of the spark plug is likely to break. In all of the above cases, it is necessary to replace the diesel glow plugs.
Replacing spark plugs (glow plugs in diesel)
In principle, the work of replacing spark plugs is not difficult:
- when the engine is not running, you need to remove the high-voltage wire from the spark plug (do not pull on the wire itself - only on the rubber protective cap!);
- Using a special key or spark plug head, unscrew the spark plug (for ease of operation, a cardan adapter for the key may be required);
- In place of the removed one, you need to screw in a new spark plug (it is important not to lose the metal sealing ring). In some cases, to make it easier to tighten the spark plug, it is recommended to lubricate the threads with an anti-seize agent (however, you should not allow it to come into contact with the spark plug electrodes!);
- tighten the spark plug until it is tightly pressed through the o-ring to the cylinder head (it is important not to overdo it - so as not to break the “soft” aluminum thread of the head!);
- Place a high-voltage wire on the spark plug and pull the protective cap tightly onto the contact.
In practice, this initially simple algorithm can become significantly more complicated if access to the spark plugs is difficult. Unfortunately, the layout of modern gasoline engines (especially boxer engines) can be so tight that the price of replacing spark plugs must include additional work.
However, contrary to popular belief, “half the engine” does not need to be disassembled for this! For example, on Subaru boxer engines it is more convenient to change spark plugs from below - all you need is a lift and preliminary removal of the engine protection. You may also need special key, since ordinary locksmiths “do not allow you to turn around” in a tight space. For those who scrupulously assess the cost of replacing spark plugs, it is recommended to use iridium or platinum ones rather than regular ones - their service life is significantly higher than standard ones (see below).
Replacing glow plugs in a diesel engine passenger car as follows:
- the car is placed on flat surface, the hood opens (it is advisable to carry out the operation on a cold engine);
- the decorative plastic motor cover is removed ( Depending on the car model, this operation may not be available);
- the fasteners are unscrewed and the upper casing of the cylinder head is dismantled (to make work easier, the oil dipstick should also be removed);
- the contact wires are removed from the glow plugs;
- to unscrew the spark plugs you will need a standard tubular wrench;
- new spark plugs are installed to replace the old ones;
- the remaining operations are performed in the reverse order of disassembly.
It should be noted that before replacing glow plugs, you need to make sure that the fault lies precisely in them. Perhaps the contact control unit or the spark plug supply wire is at fault. And also a blown fuse (however, before replacing it, be sure to make sure that the problem has been fixed - otherwise new fuse will also burn!). You can evaluate the serviceability of the glow plug using a multitester or ammeter (see above). Besides, modern blocks The engine management system has a self-diagnosis function and can generate an error code indicating a spark plug defect.
What you need to do by car:
Necessity frequent replacement spark plugs indicates a disruption in the working process in a gasoline engine. In this case, candles can act as a kind of “indicator”. So black deposits indicate that oil has entered the combustion chamber of the engine (wear piston rings, oil seals or malfunction of the crankcase ventilation system). A red-red coating is a sign of the use of low-octane fuel, generously diluted with iron-containing additives.
Danger of use bad gasoline lies in its tendency to detonate - this is a direct threat rapid wear cylinder-piston group and valves. Well, potholes on the working surface of the spark plug or a broken side electrode indicate that detonation has already “worked” on the engine (and the broken contact safely got into the cylinder!).
Spark plug life
It is recommended to change spark plugs for gasoline engines every 30 thousand kilometers. However, the actual condition of the spark plugs greatly depends on operating conditions. At frequent work If the motor is “half-pedaled” (at low frequency and load), carbon deposits are likely to form and the life of the spark plugs will decrease. Wear on the piston rings and oil penetration into the combustion chamber also increases carbon deposits. Poor quality gasoline(especially modern “ferrous”, with a high content of ferrocenes) covers the candles with a red coating. All this can reduce the resource to 15 thousand km and below!
Replacing glow plugs with diesel cars, as a rule, is carried out no earlier than a mileage of 60 thousand km. It should be noted that diesel spark plugs“work” in more gentle conditions, which ensures their increased mileage.
What are the consequences of untimely replacement?
Failure of the spark plugs makes the engine impossible to operate in principle. But operating an engine with faulty spark plugs leads to loss of power, increased toxicity of exhaust gases and deterioration of engine efficiency.
Besides, faulty spark plugs lead to increased engine vibration (motor “troits”), which negatively affects the service life of the supports and transmission. A non-functioning spark plug in the cylinder leads to intense washout of the oil film, which not only dilutes the oil in the crankcase with fuel (significantly reducing its service life), but also increases wear on the rings and cylinder bore. As a result, dubious savings on replacing spark plugs result in an increase in overhaul engine!
As for glow plugs, replacing them on a diesel engine is necessary to maintain the engine’s ability to start successfully in the cold season. If the spark plugs are defective, or their condition is generally unclear, at the most inopportune moment you may find yourself with a completely serviceable, but not starting diesel engine - and even with a completely discharged battery from long attempts to revive the engine with the starter!
On motors of a “classical” design (without electronic control) identifying a faulty spark plug is quite simple: you can gently touch it during operation ( defective spark plug will be cold). Another way: one by one remove the high-voltage wires from the spark plugs of a running engine. If the nature of the work changes, then the spark plug worked properly until the wire was removed. If the sound of the engine remains unchanged, the spark plug is faulty!
However, in modern engines With electronic system control any manipulations with high voltage wires(such as “spark tests”) can lead to the failure of their expensive injection controller!
At one time (back in the era carburetor engines) engineers were looking for different ways increasing combustion rate working mixture in the engine cylinders. After all, what more speed, the higher all indicators (including engine power and efficiency). At the same time, in gasoline engines There is always a danger of detonation - self-ignition of the last part of the charge in the cylinder, pressed by already burned gases that have a very high temperature and pressure. This effect is especially pronounced if the flame front in a “wedge” type combustion chamber goes from the wide end to the tapering end.
That is why, to help the “clamped” part of the charge, two spark plugs were installed in the cylinder, working synchronously. A similar solution was widely practiced on Alfa Romeo models, known for their Italian sporting spirit. In general, the idea of installing several spark plugs in one cylinder came from aviation. True, for piston aircraft engines this decision was dictated not so much by the fight against detonation, but by the mandatory duplication of all important nodes(including elements of the ignition system).
Slightly different from gasoline. The ignition of the fuel-air mixture does not occur from the spark of the spark plug, but from compression. To start the engine, especially in winter (and for a diesel power unit, “winter” begins at a temperature of about + 5 degrees), it is necessary to warm up the combustion chamber. Pin and ceramic candles incandescent
These devices are capable of heating the air in the injection zone to a temperature of 850 to 1000 degrees Celsius within a few seconds. Once the engine has started, they continue to operate until the coolant temperature rises to 75 degrees Celsius.
Types of glow plugs
Pin
There are two types of glow plugs for diesel engines:
- pin;
- ceramic.
They have a similar design, the difference lies in the working element. In pin type, the working element is a glow pin made of a thermo-corrosion rod, tightly pressed into the spark plug body. Inside it is compacted magnesium oxide powder and a spiral thread. 
The electrical circuit of such a candle is quite simple. Current is supplied to the head, from it through a conductive rod to a metal filament consisting of two resistors - a heating and a control coil.
- The resistance of the first is constant, independent of temperature;
- the second spiral has a positive temperature coefficient.
The principle of its operation is that the higher the temperature of the motor, the lower the heating temperature of the spark plug (when the control coil heats up, its resistance increases and less current is supplied to the heating coil). Such a spark plug heats up to 850 degrees, its operating time ranges from 4 seconds to two minutes and depends on the temperature of the motor and the parameters of the spark plug itself.
The duration of fuel heating is regulated by a control unit that monitors the readings of the coolant temperature sensor. The instrument panel has warning lamp, indicating that the heating is working. When it goes out, the engine is ready to start. There are two options for turning on the glow plugs: the ignition key is turned to the second position, or preheating turns on when the driver's door is open. Plugs that continue to burn after the engine starts help reduce warm-up time and provide more complete combustion fuel, thereby reducing emissions of harmful substances.
Ceramic
Ceramic glow plugs are the second type of heating devices. Her electrical diagram no different from the previous one. The working element of such a candle is a ceramic rod, inside of which there is a ceramic heating element. Within two seconds, the rod is heated to 1000 degrees, resulting in quick start diesel, like a gasoline power unit, without the “swing” characteristic of most diesel engines.
The heating voltage is not constant, it has three phases. At the stage quick warm-up it ranges from 9.8 to 11.5 V, while the rod heats up to the maximum possible temperature. When the engine starts, the supplied voltage gradually decreases to a level below the voltage on-board network car: in the second phase up to 7 V, in the third – up to 5. 
In addition to these three phases, there is an intermediate glow mode designed to restore the diesel particulate filter. This helps improve combustion conditions during the reduction process.
Ceramic glow plugs have a number of advantages over pin plugs with a heated spiral. The most significant is a higher heating temperature, which provides better job spark plugs during cold start, less toxicity of exhaust gases, more long term service, greater efficiency (their heating temperature at the same voltage is much higher).
Manufacturers often install diesel engines spark plugs with built-in pressure sensor. Its readings help to adjust the heating temperature of the candle and increase its efficiency.
Checking the condition of the glow plugs
The condition of the glow plugs must be carefully monitored and changed in a timely manner, especially if the car is operated in winter (how often the car manufacturer will indicate how often to change). Firstly, before winter you need to check their performance, since even one broken spark plug will not allow you to start the engine when negative temperature. If the check reveals one, then it is better to change the entire set, since the rest may soon fail.
There are two safe way check the spark plugs. The first requires the participation of two people. You will need to unscrew the nozzles, after which one person will look into the wells, and the second will turn the key to the pre-start position. Working spark plugs will turn red from heating. However, this method is not suitable for everyone, because... On some engines, spark plugs are simply not visible through the injector wells.
The second way to check the serviceability of the spark plugs is with a multimeter. You need to select the circuit check mode, then touch the spark plug body with one probe and its cap with the other. If the circuit is closed, then it works, otherwise it needs to be changed. 
On many modern cars The glow plugs are checked in self-diagnosis mode, and the electrical wiring diagram is supplemented with an indicator on the dashboard indicating a breakdown.
Under normal operating conditions, glow plugs need to be changed on average once every 60 thousand km. If the machine is constantly operated under extreme conditions, then it would be a good idea to check their performance at least once a season, and change them either at frequent intervals or when they fail.
Glow plugs must be changed with caution. They are quite fragile and often break when trying to unscrew them. If this happens, you will have to take the car to a service station or remove the cylinder head yourself to drill out the broken spark plug and cut a new thread.
Signs and causes of glow plug failure
It often happens that the engine, for no apparent reason, starts with difficulty and runs unevenly when it is cold. A related symptom may be exhaust white. As a rule, the reason lies in the breakdown of the glow plugs. If they have recently been changed and their service life has not reached the end, most likely it is a manufacturing defect and one of the spark plugs has stopped working. You need to check everything and replace the faulty one. It is quite difficult to notice a malfunction in the summer. It begins to appear as the ambient temperature decreases.
If two fail at once, then the engine most likely will not be able to start at all. Simultaneous failure more spark plugs are unlikely, and you will have to check the electrical wiring or control unit.
A candle may stop working in several cases: it has reached the end of its life, there are problems with fuel equipment or electrical wiring. In the first case, the entire set of spark plugs is checked and replaced; in the rest, you will need to check the injectors, control relays, and wires one by one.
