BMW 1989-1995 525i Service Manual page 205

RADIATOR AND COOLING SYSTEM
170 Radiator and Cooling System
170-1
GENERAL
170-1
Coolant Pump and Thermostat . . . . . . . . . . . . . 170-1
Radiator, Expansion Tank,
and Cooling Fans 170-1
Warnings and Cautions 170-2
TROUBLESHOOTING
170-2
Pressure Test 170-2
Thermostat Quick Check . . . . . . . . . . . . . . . . . . 170-3
Temperature Gauge Quick Check. . . . . . . . . . . 170-3
Cooling Fans Quick Check 170-3
DRAINING AND FILLING COOLANT
170-5
To drain and
fill
coolant 170-5
To bleed cooling system 170-5
COOLANT PUMP REPLACEMENT
170-6
To replace coolant pump (M20 engine ) 170-6
To replace coolant pump (M30 engine) 170-7
GENERAL
This section covers repair and troubleshooting information
for the engine cooling system . For heater core and related
heating and air cond itioning components, see 640 Heating
and Air Conditioning.
Coolant Pump and Thermostat
A centrifugal-type coolant pump is mounted on the front of
the cylinder block. The pump is crankshaft-driven by a drive
belt and circulates coolant throug h the system whenever the
engine is running. A thermostat controls the flow of coolant
into the radiator.
When the engine is cold the thermostat is closed so coolan t
bypasses the radiator, recirculating from the engine directly
back to the pump. When the engine reaches operating tem-
perature , the thermostat opens and coolant circulates through
the whole system including the radiator.
Radiator, Expansion Tank, and Cooling Fans
The radiator is a crossflow design. A translucent 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 ex-
changer (ATF cooler). See Fig. 1.
To replace coolant pump (M50 engine) 170-8
To replace coolant pump (M60 engine) 170-9
THERMOSTAT REPLACEMENT
170-10
To replace thermostat. . . . . . . . . . . . . . . . . . 170-10
RADIATOR REMOVAL
AND INSTALLATION
170-1 1
To remove and install radiator . . . . . . . . . . . 170-11
COOLING FAN REMOVAL
AND INSTALLATION
170-12
To remove and install cool ing fan . . . . . . . . . 170-12
TABLE
a. Auxiliary Fan Temperature Switch Tests . .... 170-4
b. Cooling System Capacities . . . . . . . . . . . . . . . 170-5
B
I
~-
-'
e 11,67
A. Expansion tank C. Coolant level sensor
B. Radiator drain screw D. Auxiliary fan temperature switch
Fig . 1. Radiator assembly lor M20 and M50 engines.
The primary cooling fan is mounted to the front of the cool-
ant pump through a fan clutch . The fan clutch is a viscous fluid
coup ling that controls the speed of the fan based on engine
compartment temperature.
A two-speed electric auxiliary cooling fan is mounted be-
hind the front grill and in front of the radiator. The fan is prima-
rily used for the AlC system , but also operates when the
coolant temperature exceeds a predeterm ined level.
GENERAL