Information On Spark Plugs
Information On Spark Plugs: The 1989 Chryslers Users Manual for the Saratoga says that only Champion spark plugs RN12 YC4 should be used. Nontheless German workshops use RN11 YC4 or RN9 YC4 ... !
On Champion and NGK spark plugs the R stands for 'integrated Resistor' to avoid radio interference. The N stands for the type of plug (windings, diameter), the YC4 gives additional informations. The numbers after N -usually 7 to 12- indicate the temperature range. The higher the value, the 'hotter' is the plug. This means: a car used on short-distances only needs a plug with a higher value, because the engine runs on usually lower average temperatures. A car mainly used on long distances and/or higher average speed needs spark plugs with lower number, which can withstand the much higher engine temperatures better and guarantee good sparks all the time.
The Chrysler Users Manual is developed and written in the USA, where average speed is much lower than in Europe. Cars in Europe were often used under high average speed for long times. A 'hotter' spark plug (with higher number) would burn out in a very short period of time - and lead to problems or even damage the engine. A too 'cold' spark plug used on a car in short distance driving would never come upon estimated working temperature. This would cause high fuel consumption and also lead to problems, like oil thinning, misfiring, bad start behavior and so on.
Older Bosch spark plugs use a naming like W200 T35, where the value after the W indicated the temperatur range. On Bosch plugs the higher value indicated a 'colder' plug. For example a W135 plug heats up faster than a W200. The value after T indicates the length and diameter of the plugs winding.
Last Update 30. January 1997
© 1997 by Peter H. Wendt