The game is worth the candle
In currently used engines, the running time of a candle is estimated at an average of 30-45 thousand. km, but there are situations when an earlier replacement is required.
When there is “something wrong” in the engine, it does not start well, runs rough, stalls, or increases fuel consumption, this is the reason most drivers turn to a mechanic.
With the electronics used in modern ignition systems, this is the right thing to do, because it is difficult to determine the cause on your own, although one of the possible causes can only be a faulty spark plug. 
In currently used engines, the plug life is estimated at an average of 20 million cycles, which can be approximately estimated at 30-45 thousand. kilometers traveled, but there are situations when an earlier replacement is required. This applies, for example, to gas-fired (LPG/CNG) engines, where this is due to heavier operating conditions (mainly slower combustion and higher temperatures). The poor quality of the fuel used is also an unfavorable factor affecting the condition of the spark plug.
What do you need for a candle?
The main task of the spark plug is to create a stable and sufficiently strong electrical spark between the electrodes, as well as to remove heat in order to keep it below the auto-ignition limit of the fuel mixture, i.e. about 900 degrees C.
For this reason, the selection of the appropriate type of spark plug for each type of engine is particularly important. It is specified by the engine manufacturer, recommending the use of candles of a certain design, the expected calorific value and their service life.
So there is no universal spark plug suitable for any type of engine! Any "miracle" substitutes, including multi-electrode candles, do not improve well. 
significantly affect the parameters of the engine, but prolong the life and reliability of the spark plug.
This also applies to spark plugs whose electrodes are made of expensive alloys (yttrium, platinum), the use of which is recommended where it is justified (for example, in the case of gas engines or power units of sports cars).
Cold, warm, hot
Depending on the thermal value of the so-called There are three main types of spark plugs according to the "thermal coefficient", which expresses the ability to conduct and dissipate heat.
"Hot" high calorific value, characterized by a large insulator surface that absorbs a lot of heat, "medium" heat plugs with less insulator, so that more heat is dissipated than a "hot" plug to engine components, and "cold" plugs ”, the least absorbing heat. 
"Hot" plugs are used in less stressed engines, while "cold" plugs are used in more demanding engines.
Clean or replace?
If you are cleaning, only use the electrodes themselves if there is a slight build up of soot, using a very soft brush. Sandpaper or sandblasting is a thing of the past. With current availability and relatively low prices, it is better to replace the spark plugs with new ones, following the recommendations of the engine manufacturer.
Can we do it ourselves? Unfortunately, due to the placement of candles, this simple operation is increasingly not possible without special tools. When saving 
old car owners can do this carefully and carefully.
One of the basic rules is to screw the candle in with your fingers until resistance is felt, and then tighten it with a wrench. This will prevent damage to the socket threads.
A badly inserted spark plug usually results in a costly head repair.
When replacing spark plugs, it is also worth carefully inspecting the ignition wires and their connections, and if there is one, check the ignition device, on which the performance of the entire system depends.
Prices for individual spark plugs
car model | Bosch | Price (złoty) | NGK | Price (złoty) | I take | Price (złoty) |
Fiat Panda 1.1 | FR78 YR7DE | 20,87 25,79 | BKR5E2 In Line16 | 16,11 9,90 | ZF2 XF7 | 10,33 22,29 |
Skoda Fabia 1.4 | FR78 F7DC | 20,87 12,49 | BKUR5ET-10 In Line17 | 24,86 6,81 | 14FR-8DPU2 | 21,70 |
Toyota Corolla 1.6 VVT-i | FR78 FR7KCX-11 | 20,87 11,46 | BKR5EYA-11 BKR6EY-11 | 16,11 16,11 | 14FR-7KUOKS | 14,20 |
Ford Focus 1.6 | HR8MEV | 14,91 | PTR5A-13 In Line25 | 39,26 38,36 | - | - |
Renault Laguna 1.8 16V | FR7DP + FR7DC+ | 16,88 12,49 | BKR6ES V Line 28 | 13,55 15,31 | UXF79P4 | 44,08 |
Audi A6 2.4 | - | - | BKR6EKUB | 32,12 | 14-FGR-6DDU | 41,92 |
BMW 525i | FGR7DQP | 49,34 | BKR6EKVP In Line30 | 54,09 52,80 | 14-FR- 7DUQP7 | 48,90 |
