Mechanical Thermostat (M52 Engine; Electrically Heated Thermostat; Radiator And Expansion Tank; Mechanical Cooling Fan With Viscous Clutch - BMW 5251 Service Manual

-
I
Radiator and Cooling System
Mechanical thermostat (M52 engine)
4
The mechanical thermostat relies on coolant temperature to
operate. While coolant is cold, it remains closed, and circu-
lating coolant bypasses the radiator for rapid engine warm
up. At higher coolant temperature, the thermostat progres-
sively opens to allow coolant flow through the radiator, thus
controlling engine temperature. Port A restricts coolant flow
from radiator, and port B restricts coolant flow to radiator.
Electrically heated thermostat
4
The electrically heated thermostat is DME map-controlled.
The engine control module (ECM) activates the thermostat to
maintain engine coolant temperature within a narrow range.
In case of failure of the electronics, the mechanical function of
the thermostat acts as a fail-safe.
Radiator and expansion tank
The radiator is a crossflow design. An expansion tank pro-
vides 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).
Mechanical cooling fan with viscous clutch
The mechanical cooling fan is belt-driven via a viscous fluid
coupling (clutch) attached to the front of the coolant pump.
The fan clutch controls the speed of the fan based on the tem-
perature of the air flowing through the radiator core.
Electric (auxiliary) cooling fan
The electric cooling fan is mounted on the bumper side of the
radiator.
In models manufactured up to 911 998 (M52 or 1997 M62 en-
gine), the electric cooling fan is controlled by a dual tempera-
ture fan switch mounted in the side of the radiator.