BMW 3 (E46). Instruction - page 91

Expansion tank cap test adapter BMW
17 0 007

Cooling system (DME MS 42.0)

Coolant pump

A centrifugal-type coolant pump is
mounted to the front of the engine. The
belt-driven pump circulates coolant
through the system whenever the engine
is running.

Thermostat

An electrically heated thermostat
regulates the engine coolant
temperature and is controlled by the
DME control module. The heated
thermostat allows the engine to be
operated at higher temperatures at idle
and at part throttle. Having the ability to
control the engine coolant temperature
electronically results in improved
emissions and performance. Problems
with the heated thermostat can be
diagnosed using a compatible scan tool.

Radiator and expansion tank

The radiator is a crossflow design. An
expansion tank provides for coolant
expansion at higher temperatures and
easy monitoring of the coolant level.

On cars with automatic transmission,
ATF is circulated through an additional
heat exchanger (ATF cooler).

Cooling fan (primary)

The are two cooling fan configurations
used on the cars covered by this
manual, depending on transmission

application.

On cars with automatic transmissions,
the main fan is electric and mounted on
the bumper side of the radiator. The fan
is controlled by the DME control module
via the output final stage. Additionally a
belt-driven fan via a viscous fluid
coupling (clutch) is attached to the front
of the coolant pump. The fan clutch
controls the speed of the fan based on
engine compartment temperature.

On cars with manual transmissions, a
single multi-speed electric cooling fan is
used. The fan is mounted on the engine
side of the radiator and controlled by the
DME control module via the output final
stage.

On both configurations, the output final
stage is mounted on the fan housing,
next to the fan motor. The fan is
operated using a pulse width modulated
(PWM) signal and is protected by a
50-amp fuse. Electric fan activation is
based on the following inputs to the
ECM:

Radiator outlet temperature

Catalyst temperature (calculated
temperature)

Vehicle speed

Battery voltage

A/C pressure (calculated pressure)

When the vehicle is first started, The
ECM activates the electric fan briefly at
20% of its maximum speed, then
switches off. This is for diagnostic
monitoring. The voltage generated by
the fan when it slows down (acting as a
generator) must match the stored `rpm'

values in the fan power output stage to
confirm that the fan is operating
correctly.

Note:

If the ECM stored a cooling fan
fault, check that the fan is not
seized and that is spins freely.

When A/C is switched ON, the
electric fan is not immediately
turned on.

After the engine is switched OFF,
the fan may continue to run at
varying speeds for up to 10 minutes,
based on calculated catalyst
temperature.

Warnings and cautions

The following warnings and cautions
should be observed when working on
the cooling system.

WARNING!

At normal operating temperature
the cooling system is
pressurized. Allow the system to
cool as long as possible before
opening-a minimum of an
hour-then release the cap slowly
to allow safe release of pressure.

Releasing the cooling system
pressure lowers the coolant
boiling point and the coolant may
boil suddenly. Use heavy gloves
and wear eye and face protection
to guard against scalding.

Use extreme care when draining

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