Improper testing procedure (applying 12 volts directly to a glow plug designed to operate on 6 volts) Incorrect engine timing Improper fuel injector spray pattern Continual cycling of the glow plugs

The following signs most likely indicate that it’s time to change a vehicle’s glow plugs. * Vehicle won’t start * Vehicle starts only after excessive cranking * Excessive cranking can cause the engine oil to be diluted with fuel, which could adversely effect the life of the engine * Vehicle idles roughly after initial start-up * Excessive exhaust emissions after initial start-up

Unlike gasoline engines which use a spark plug to ignite an air/fuel mixture, diesel engines rely on the heat of highly-compressed air to ignite a precise amount of fuel to initiate combustion. Heating the air to a minimum starting temperature of 850°C is critical for diesel engine start-up. In low temperatures, factors such as cold intake air and cold cylinder walls hinder the attainment of the necessary starting temperature. In these situations, glow plugs function as an additional heat source to bring the intake air up to the temperature necessary to initiate the combustion cycle.