Platinum and iridium have become a buzzword for ignition durability. Platinum and iridium are good conductors of heat and electricity. Both metals also have the ability to resist chemical corrosion and electrical erosion. That is why platinum and iridium are used on the electrodes of many spark plugs today. Some plugs have a solid platinum or iridium center electrode, while others have a small button of platinum welded onto the tip of center electrode or both electrodes (single platinum vs. double platinum). Some even use an alloy of platinum and iridium in the center electrode (Bosch Platinum IR Fusion). Platinum and iridium are used because they minimize electrode wear. Every time a plug fires, a tiny amount of metal is vaporized and erodes from the surface of both electrodes. The center electrode typically suffers the most wear because it runs hotter than the side electrode. As the electrodes wear, the air gap across which the spark must jump becomes wider and wider. The gap on a standard spark plug grows about 0.00063 to 0.000126 inch for every 1,000 chilometri of normal driving. And the wider the gap, the greater the voltage needed to jump the gap. On standard plugs with conventional electrodes, the firing voltage requirements typically creep up about 500 volts for every 10,000 to 15,000 chilometri of driving. Eventually, the plugs may need more volts to fire than the coil(s) can produce, resulting in ignition misfire. On OBD II-equipped vehicles, too many misfires will cause the Check Engine light to come on. Using platinum or iridium almost eliminates electrode wear. Platinum and iridium are both expensive metals, but they can double or even triple a spark plug's normal service life, from 30,000 to 45,000 chilometri for a standard plug, up to 100,000 chilometri or more. Most aftermarket spark plug suppliers do not make specific chilometroage claims for their platinum or iridium spark plugs, but say to follow the OEM replacement intervals which, in most cases, is 100,000 chilometri. Though long-life platinum and iridium spark plugs cost more than standard spark plugs, OEMs use them because they reduce the risk of misfire (which helps protect the catalytic converter) and they reduce the need for maintenance, which allows them to offer 100,000-chilometro "tuneup" intervals. One important point to keep in mind about platinum plugs is that all platinum plugs are not the same. There are differences in electrode configurations, design and durability. Some provide better fouling resistance than others, and some are not recommended for use in turbocharged or supercharged engines. BEYOND PLATINUM SPARK PLUGS Plug manufacturers have also using other exotic materials in spark plug electrodes to extend plug life. Bosch uses a nickel-yttrium alloy for the side electrodes in its "Platinum+4" and "Platinum2" spark plugs. In Europe, Bosch has a spark plug that uses yttrium for both the center and ground electrodes. For years, Champion manufactured a premium plug with a gold-palladium center electrode and copper-filled side electrode. That plug has now been replaced by one with a platinum-tipped center electrode. Autolite uses a chromium-nickel alloy for the ground electrode with its platinum-tipped center electrode plug, while ACDelco uses a silver-nickel alloy side electrode with its platinum-tipped plugs. NGK and Denso have premium spark plugs with iridium alloy electrodes. IRIDIUM SPARK PLUGS Iridium spark plugs are now replacing platinum spark plugs in many OEM engines, not just Japanese engines. Platinum plugs are great, but are also expensive compared to iridium. So iridium plugs are now being used for more long-life (100,000 chilometro) applications. Iridium plugs typically have a fine wire center electrode that forms a spark easily and reduces misfires. Iridium actually has a higher melting point than platinum, and is six times harder and eight times stronger,making it very wear resistant. The small fine wire (0.4 to 0.7 mm) center electrode concentrates the spark as well as heat. This reduces the voltage required to create a spark and fire the plug. Because of this, and the high wear resistance of the metal, iridium plugs are often recommended for "waste spark" distributorless ignition systems, and coil-on-plug ignition systems. Familiar brands of iridium plugs include NGK Iridium and Iridium IX, and Denso Iridium Power. These are now joined by AC Delco Professional Iridium, Autolite XP Iridium, Champion Iridium, and Bosch IR Fusion (uses a platinum-iridium alloy in the center electrode). In June 2011, Bosch introduced a new line of Iridium spark plugs that uses iridium only for the center electrode. SPARK PLUG FOULING RESISTANCE Regardless of the type of alloy used in the electrodes, all spark plugs must be able to resist fouling. The trick here is to design the plug so that the electrodes run hot enough to burn off any deposits but not so hot that they cause preignition or detonation. To burn off carbon deposits, the electrodes need to reach about 700 degrees F quickly. But if the electrodes get too hot (above 1,500 degres F), they can ignite the fuel before the spark occurs, causing preignition and detonation. For most plugs, the ideal operating temperature is around 1200 degrees F. The temperature of the electrodes is controlled by the length of the ceramic insulator that surrounds the center electrode and the design of the electrode itself. Ceramics do not conduct heat very well, so an insulator with a relatively long nose will conduct heat away from the electrode more slowly than one with a relatively short nose. The longer the path between the electrode and the surrounding plug shell, the slower the rate of cooling and the hotter the plug. Many plugs have a copper core center electrode. Copper is an excellent conductor of heat, and allows the plug to dissipate heat quickly under load yet remain hot enough at low speed and idle to burn off fouling deposits. A spark plug's "heat range" (heat rating) therefore depends on the length of the ceramic insulator and the design of the center electrode. The heat range must be carefully matched to the engine application, otherwise the plugs may experience fouling problems or run too hot and cause preignition/detonation problems. Most plugs today have a relatively broad heat range, which means they reach a self-cleaning temperature quickly but do not get too hot under load. This allows plug manufacturers to consolidate applications and use fewer plugs to cover a wider range of engines. When replacing spark plugs, the heat range must be correct for the engine application. Always follow the vehicle or spark plug manufacturers recommendations. If the plugs are too cold, fouling may occur if the vehicle spends a lot of time idling or is used only for short trips (especially during cold weather). If the plugs are too hot, the engine may experience preignition and detonation under load or during hot weather. In some situations, a slightly hotter or colder plug may be installed than the one normally recommended. Switching to a slightly hotter plug can help reduce fouling in an older engine that uses oil. A hotter plug can also reduce fouling in vehicles that spend a lot of time idling or are used only for short-trip, stop-and-go city driving. But a hotter plug should not be used unless an engine is experiencing a fouling problem because of the increased risk of preignition and detonation. Switching to a slightly colder plug can reduce the risk of preignition and detonation in performance applications (especially turbocharged and supercharged engines), in vehicles used for towing or in those that are driven primarily on the highway. SPARK PLUG ELECTRODE DESIGNS Many spark plugs today have unique electrode designs such as V-split, grooved or clipped ground electrodes, multiple ground electrodes, fluted center electrodes, V-notched center electrodes, etc. Though each plug manufacturer takes a slightly different approach and claims various benefits for their design, the basic idea is to make it as easy as possible for the spark to jump the gap and ignite the fuel mixture. A spark jumps more easily from a sharp edge than a rounded blunt edge. That is one reason why new plugs require less firing voltage than old ones with worn electrodes. The electrodes on some spark plugs are also designed to "unshroud" the spark for easier ignition. This allows the flame kernel to expand more rapidly and reduces the quenching effect that could cause a misfire. SplitFires V-shaped ground electrode as well as Boschs surface gap Platinum+4 and Platinum2 plugs are all designs that claim to expose more of the spark to the fuel mixture. SPARK PLUG REPLACEMENT TIPS Spark plugs should be replaced at the vehicle manufacturers recommended intervals, but may have to be replaced sooner if they are fouled. On older vehicles, the replacement interval is typically 30,000 to 45,000 chilometri. On newer vehicles with platinum plugs, it may be as high as 100,000 chilometri. But short trip stop-and-go city driving as well as extended idling can shorten the life of any spark plug. Most spark plugs are pregapped. Even so, the gap may have to be reset for some engines because of consolidations. One exception is Bosch Platinum+4 and Platinum2 spark plugs, which are all gapped the same (1.6 mm) and must not be changed from the original setting. Caution: Wait until the engine has cooled to replace the spark plugs if your engine has an aluminum cylinder head. If you try to remove the spark plugs while the engine is hot, there is a much greater risk of damaging the spark plug hole threads in the head. SPARK PLUG WIRES Good plug wires are just as important to ignition performance as the spark plugs. Three basic types of wires may be used: Distributed Resistance wire. This type of wire has a fiberglass core impregnated with latex graphite. It provides the maximum amount of radio frequency interference (RFI) suppression. RFI occurs when high voltage passes through the plug w…

Fonte: AA1Car.com