1. Necessity of preheating system
At a cold engine starting, the compression heat escapes from the compression chamber even if there is adequate compression. In some cases, the injected fuel does not rise to the ignitable temperature. Therefore, the preheating system is necessary to improve ignition performance. By heating the air before a cold engine starting, the preheating system improves engine startability. Also, diesel knock and white smoke are reduced by heating the air for a certain amount of time according to the coolant temperature even after starting.
The latest Toyota vehicles feature glow plugs with self-controlling temperature. A control coil is built into the glow plug, in which the resistance increases as temperature rises. The increased resistance of the coil reduces the amount of current to the thermal coil, which is connected in series to the control coil. By reducing the amount of current, the temperature of the glow plug does not rise as much. The temperature of glow plug rises to approx. 90C (1,472 F).
The previous glow plug, which did not feature self-controlling temperature featured a system when the glow plug resistors were set in series, reducing the current flowing into the glow plug.