There are three basic diagnostic criteria for spark plugs: good, fouled and overheated. The firing end appearance also depends on the spark plug tip temperature. Tip Temperature and Firing End Appearance A projected style spark plug firing tip temperature is increased by 10☌ to 20☌. In identical spark plug types, the difference from one heat range to the next is the ability to remove approximately 70☌ to 100☌ from the combustion chamber. This may lead to pre-ignition/detonation and expensive engine damage.
If the tip temperature is higher than 850☌ the spark plug will overheat which may cause the ceramic around the centre electrode to blister and the electrodes to melt.
These accumulated deposits can result in spark plug fouling leading to misfire. If the tip temperature is lower than 500☌, the insulator area surrounding the centre electrode will not be hot enough to burn off carbon and combustion chamber deposits. Whether the spark plugs are fitted in a lawnmower, boat, or a race car, the spark plug tip temperature must remain between 500C-850☌. Since the insulator tip is the hottest part of the spark plug, the tip temperature is a primary factor in pre-ignition and fouling. The insulator nose length is the distance from the firing tip of the insulator to the point where insulator meets the metal shell. The heat range measurement is determined by several factors the length of the ceramic centre insulator nose and its’ ability to absorb and transfer combustion heat, the material composition of the insulator and centre electrode material. Rather, the heat range is a measure of the spark plug’s ability to remove heat from the combustion chamber. The materials/construction of the centre electrode and porcelain insulatorĪ spark plug’s heat range has no relationship to the actual voltage transferred though the spark plug.The rate of heat transfer is determined by: The heat range is defined as a plug’s ability to dissipate heat. The spark plug works as a heat exchanger by pulling unwanted thermal energy away from the combustion chamber, and transferring the heat to the engine’s cooling system. It is important to remember that spark plugs do not create heat, they can only remove heat. This is called “Thermal Performance”, and is determined by the heat range selected. The temperature of the spark plug’s firing end must be kept low enough to prevent pre-ignition, but high enough to prevent fouling. A sufficient amount of voltage must be supplied by the ignition system to cause it to spark across the spark plug’s gap. Spark plugs transmit electrical energy that turns fuel into working energy. To remove heat from the combustion chamber.The spark plug has two primary functions: The experienced tuner can analyze these symptoms to track down the root cause of many problems, or to determine air/fuel ratios Like a patient’s thermometer, the spark plug displays symptoms and conditions of the engine’s performance. Spark plugs are the “window” into your engine (your only eyewitness to the combustion chamber), and can be used as a valuable diagnostic tool. The information contained in this guide applies to all types of internal combustion engines: two stroke engines, rotary engines, high performance/racing engines and street vehicles. This guide was designed to assist the technician, hobbyist, or race mechanic in understanding, using, and troubleshooting spark plugs. Numerous questions have surfaced over the years, leaving many people confused. Spark plugs are one of the most misunderstood components of an engine.
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