General Information
The quick warming - up system is installed to shorten the time for warming - up the engine when cold.
The quick warming - up of the engine is obtained by choking both the intake air and exhaust gasses to increase the engine temperature quickly. With this the cooling effect of intake air is reduced considerably and the compression pressures are raised.
The quick warming - up system is only active when the outside temperature is below 8 °C / 47 °F and with an engine temperature lower than 73 °C / 163 °F.
When the above conditions are fulfilled and when the engine is at idle speed a throttle valve in the intake manifold and a throttle valve in the exhaust manifold are closed by means of vacuum controlled valves. A vacuum delay valve will cause the throttle valve in the intake manifold to close approx. 10 s. later than the throttle valve in the exhaust manifold.
The quick warming - up system can be deactivated by the driver by means of the quick warming - up switch in the instrument panel.
When the engine is not at idle speed but at a low output speed the throttle valve in the exhaust manifold is half closed. The throttle valve in the intake manifold is closed fully.
A vacuum regulating valve will slightly open the throttle valve in the intake manifold when the vacuum in the intake manifold raises above a threshold value.
When the quick warming - up system is activated the engine idle speed is increased by means of a vacuum controlled actuator at the injection pump.
When the engine has warmed up above 80 °C / 176 °F or when the outside air temperature raises above 15 °C / 59 °F or when the requested output of the engine is more then half load the quick warming - up system is switched off.
For engines without exhaust gas recirculation the status of the engine is monitored by a switch at the injection pump lever and at the accelerator pedal. For engines with exhaust gas recirculation the status of the engines is determined by the EGR control unit.