Intake Manifold Heating

Models with 4-cylinder engines and Mono-Motronic system

From the Mono-Motronic fuel mixture preparation unit, the air-fuel mixture passes through the intake manifold into the cylinders.

If the intake manifold is cold, a significant part of the mixture condenses on the inner walls of the manifold and does not reach the combustion chambers as vapor. This causes losses and thus increased fuel consumption. This problem can be reduced by double heating of the intake manifold.

When the engine is cold, the electric intake manifold heater is activated. It consists of an electrically heated grid screwed into the intake manifold below the mixture preparation unit. The grid's pins serve not so much as passive protection as to increase the surface area of the heating element. This heater operates only up to a coolant temperature of approximately 65 °C. Then the current is switched off.

The thermal switch (shown in the wiring diagrams as Engine Coolant Temperature Sensor – G62) does not switch the heater directly. G62 provides temperature information to the Mono-Motronic control unit, which in turn activates the relay in the auxiliary relay box under the instrument panel to supply power to the heating grid.

At higher temperatures, the intake manifold is heated by the coolant. For this purpose, additional coolant is routed from the main coolant flow through a special passage in the intake manifold.