1. Vehicle won’t start
2. Vehicle starts only after excessive cranking
3. Excessive cranking can cause the engine oil to be diluted with fuel, which could adversely effect the life of the engine.
4. Vehicle idles roughly after initial start-up
5. Excessive exhaust emissions after initial start-up.

You can replace OE glow plugs with Bosch with complete confidence. Bosch is currently the OE glow plug on most European diesel vehicle applications. And for Domestic and Japanese vehicle applications, Bosch Glow Plugs are designed to meet and/or exceed the OE glow plug specifications.

If one glow plug fails, chances are the others won’t be far behind. To minimize vehicle down-time and save on labor costs, Bosch recommends changing all glow plugs at the same time.

Excessive voltage is the leading cause of glow plug failure. Glow plugs are designed to operate within a temperature range of 850° – 1100°C. During operation, the glow plug controller switches current to the glow plug for a specific period of time to allow for proper heating. However, when the controller fails, current could be applied for a longer than specified time causing the temperature of the glow plug to exceed the 1100°C upper limit. Under these conditions, the glow plug overheats causing the casing to swell, split or burst which allows air to enter the coil area causing immediate failure.

Other causes of glow plug failure include:

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

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.

Bosch’s revolutionary Duraterm® glow plug technology utilizes a self-regulating control system that reduces glow wait time by more than 50%. The patented dual-control regulating and heating coil effectively directs current draw, enabling the glow plug to reach higher temperatures more quickly for faster engine start-up. The regulating coil keeps the heating element within the 1000˚ – 1100˚C optimal temperature range, preventing engine damage due to over voltage/overheating.

Bosch Duraterm® technology is available for the majority of diesel car and light truck applications. Other applications employ standard glow plug technology per OE specifications.