The function of the spark plug is to introduce the ignition energy into the combustion chamber and to initiate combustion of the compressed air-fuel mixture. It accomplishes this task by generating a spark between its electrodes, which then generates the required heat to ignite a smooth burn of the air/fuel mixture. The spark plug is an important factor in determining optimal performance and reliable functioning of an engine. It must permit reliable cold starting, it must guarantee that there is no misfiring during acceleration, and it must withstand the engine being operated for hours on end at maximum power. These requirements apply throughout the entire service life of the spark plug. For 100 years, Bosch Spark Plugs have been designed for optimal performance, reliable functioning, and to withstand extreme operating conditions. Today, the continuously developing spark plug is a key engine system component. It plays a major role in fuel economy, clean, efficient combustion, and the reliable operation of engines and catalytic converters.

There is a large variety of different spark plug designs with more than 1,400 variations. Design variants and special materials such as platinum, silver, or yttrium allow Bosch spark plugs to be used in a wide variety of applications today. In all, Bosch has developed more than 20,000 different types of spark plugs over the last 100 years.

During operation, the spark plug is subjected to both wear and to fouling and should be replaced at regular intervals. In the course of its service life, the spark plug undergoes changes that increase the required ignition voltage. When the required voltage reaches a level that can no longer be compensated for by the voltage reserve, the result is misfiring. These changes can be caused by: Electrode wear Engine wear Abnormal operating conditions (pre-ignition, detonation, high oil consumption) Independent tests have shown that installing premium spark plugs such as Bosch's Platinum+4 improves fuel mileage by as much as 4.8% over original equipment plugs. Platinum+4 uses race-tested technology including multiple electrode paths and more pure platinum to generate strong, consistent sparks.

Reading the spark plugs provides valuable information on spark plug and engine operating conditions.
Click here to review spark plug faces.

Bosch recommends when installing spark plugs to use a torque wrench and the correct torque in ft.-lbs. As listed below:

	10mm With Gasket	12mm With Gasket	14mm With Gasket	14mm Tapered Seat	18mm With Gasket	18mm Tapered Seat
Torque Ft.-Lbs.	8-11	12-15	19-22	12-15	20-23	14-17

If a torque wrench is not available, hand tighten the plug until it is seated in the cylinder head. Spark plugs with gaskets should be tightened an additional 90°. Spark plugs with tapered seats should be tightened an additional 15°.

Most Bosch Spark Plugs are factory pre-gapped for popular vehicle applications. The gap measurements are indicated either on the box, or by the part number located on the spark plug shell.

• X suffix = .044"
• Y suffix = .060"
• Z suffix = .080"

• To widen the electrode gap, use a tool that only pulls back the ground electrode, without applying pressure to the center electrode. The tool must not be wedged between the electrodes as that may cause damage to the insulator nose.
• To close the electrode gap, carefully tap the plug, electrode first, on a hard surface, as shown in the illustration.

Detonation or "knocking" is uncontrolled combustion with a very steep rise in pressure. It is caused by spontaneous ignition of the fuel mixture, which has not yet been reached by the ignition spark. As the high-pressure waves hit the walls of the combustion chamber, their impact produces a metallic knocking sound. Failure to recognize and deal with knocking will inevitably lead to serious engine damage.

The spark plugs' heat range is an index of its capacity to dissipate thermal energy. The different characteristics of automotive engines regarding operating load, compression, engine speed, cooling, and fuel make it impossible to run all engines with a standard spark plug. The same spark plug may get very hot in one engine type, but may reach only a relatively low temperature in another. In the first case, the air-fuel mixture would ignite on the glowing parts of the spark plug projecting into the combustion chamber (pre-ignition) and, in the second case, the insulator tip would soon become so badly fouled by combustion deposits that misfiring would occur. To ensure that the plug runs between the desired temperatures, plugs with different heat capacities were developed. The so called "heat range", which is assigned to each spark plug, is used to characterize these heat dissipation capacities. A plug with a low heat range number (e.g., 2-4) indicates a cold plug that quickly dissipates heat to the engine block and cooling system, while a high code (e.g., 7-10) indicates a hot plug that retains heat. By properly selecting the heat range of the plug, it ensures that the plug will operate between the plug's designed operating range of 500-900 degrees Celsius. In this range, the spark plug will be self-cleaning, yet will not be hot enough to pre-ignite the air/fuel mixture.

To ensure optimal performance in your car, Bosch has tested each vehicle model and the various engines available for that model listed in the Spark Plug catalog or our web-page. Using a special spark plug with a thermocouple built in, Bosch engineers find the hottest cylinder in an engine and then test various spark plugs in that cylinder until the ideal plug is found. This ensures that you will always get the best performance possible.

If you have modified your engine with a performance system such as a turbocharger, supercharger, or nitrous, the recommended spark plug may not be correct. You may need to use a plug with a colder heat range to compensate for the additional heat generated by the engine. Bosch recommends that in these situations, you consult a qualified engine builder for assistance in determining the appropriate heat range.

As a rule, Bosch recommends that you follow the replacement interval listed in your vehicle owners manual, however we highly recommend that you inspect (read) your spark plugs annually and replace as required, to insure optimum engine performance.

Yes! Bosch Spark Plugs meet or exceed warranty requirements of all vehicle and engine manufacturers, and when properly installed in accordance with the recommended application, will not adversely affect the emission control system of any vehicle.

Consumers are sometimes told by an automobile dealer's service writer or mechanic that a brand of replacement spark plug cannot be used in the consumer's vehicle during the warranty period. The claim is made that use of the brand will "void the warranty", with the statement or implication that only the original equipment brand of spark plugs may be used. This, of course, tends to cast doubt on the quality of the replacement spark plug. That claim is not true. Under the Magnuson-Moss Warranty Act and general principles of the Federal Trade Commission Act, a manufacturer may not require the use of any brand of spark plug (or any other article) unless the manufacturer provides the item free of charge under the terms of the warranty.

So, if the consumer is told that only the original equipment spark plug will not void the warranty, they should request that the OE spark plug be provided free of charge. If they are charged for the spark plug, the manufacturer or dealer is in violation of the Magnuson-Moss Warranty Act.

Yes!

Perhaps the greatest innovation in spark plug design over the years is "pure platinum" technology, combined with multiple electrodes. As early as the 1960's engineers recognized the value that platinum added to automotive plugs: it provides improved corrosion and erosion resistance and imparts a longer performance life than the standard copper core center electrode plug design. The use of platinum not only broadens the heat range beyond that achieved with a copper core center electrode design, but also provides extremely consistent performance, a reliable spark and a longer performance life.

To validate the improved performance of surface air gap plugs with a pure platinum core and multiple ground electrodes, extensive testing was conducted in the laboratory and in the field:

• The first test measured the energy transfer efficiency of the four-electrode platinum plug compared to conventional and other premium plugs with a single ground electrode. This certified laboratory test measured the additional pressure generated by the spark discharge in a pressure chamber. Higher pressure equals a higher energy transfer by the spark. The test showed that the four-electrode platinum plugs transferred more energy to the air/fuel mixture resulting in improved driveablility and lower emissions.
• As a spark plug wears via erosion and corrosion, the gap between the center electrode and ground electrode gets larger. The larger the gap, the more voltage is required to produce a spark, until the capability of the ignition system is exceeded and the plug misfires. It was found that the multiple ground electrode, pure platinum center electrode plug reduces gap erosion and increasing voltage requirements over time.
• Roush Industries, an independent test lab, measured the fuel consumption for the four-electrode platinum plug, as well as, that for original equipment and other premium single ground electrode plugs. Fuel savings up to 4.8% were found in the four electrodes, platinum core plugs. Tests were conducted in accordance with Federal Test Procedure 75FTP and HFE.
• Tests for carbon fouling were simulated in a cold cell by repeatedly cooling, starting and operating the engine without letting the spark plugs reach their self-cleaning temperature. This cycle does not let the spark plug reach its self-cleaning temperature and allows the formation of carbon deposits. The tests found that the four ground electrode spark plugs had up to 33% better cold restart reliability than conventional plugs.

YES! Racing, as it has for 100 years, provides a great developmental impetus and test bed for spark plug durability and performance, and what is learned at Indy or Darlington, or Le Mans helps improve the spark plugs installed in today's cars or trucks. From the first Indy 500 won by Ray Harroun's Marmon Wasp to the last 17 Indy 500 winners, and many in between, each have used Bosch spark plugs. Many premium passenger car spark plugs use multiple ground electrodes and precious metals, such as platinum, which are a direct result of their development and testing in long distance racing.