engine overheat BMW 525i 1997 E39 Workshop Manual

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120-6
lgnition System
lgnition system, troubleshooting
Troubleshooting ignition system faults should begin with an
interrogation of the On-Board Diagnostics (OBD
II) system.
The OBD
II system detects ignition system misfire and other
related faults. When faults are detected, the OBD
II system
stores a Diagnostic Trouble Code (DTC) in the Engine Con-
trol Module (ECM) along with other pertinent fault information.
4 In addition, the Malfunction Indicator Light (MIL) will come on
if an emissions related fault is detected. Additional OBD
II in-
formation, including a DTC lookup table, can be found in
OED On-Board Diagnostics.
NOTE-
BMWmodels covered in this manual were equipped with one
of three versions of
MIL warning lights (as shown).
Misfire detection
Engine m~sfire in one or more cylinders, may be caused by a
var~ety of malfunctions in various subsystems. The OBD II
system ~ncorporated into the engine management systems is
des~gned to detect and warn of misfire faults during englne
operat~on. See OED On Board Diagnostics.
WARNING -
lgnition misfires can cause high hydrocarbon exhaust emis-
sions andcatalytic converter damage. For this reason, if a se-
vere misfire is detected, the fuel injector
will be turned off to
the specific cylinder and the
MIL will be illuminated. A misfire
may also produce an overheated catalytic converter, which
can be a fire hazard.
Oscilloscope diagnostic diagrams
One way to diagnose a faulty coil is to use an oscilloscope to
analyze spark quality with the engine running.
See Table b. lgnition secondary voltage diagnostics for
list of common ignition
coil voltage faults and related causes.

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121-9
Battery, Starter, ~lternatorl
Battery charging
Discharged batteries can be recharged using a batterycharg-
er. Remove the battery from the trunk during charging.
Prolonged charging causes electrolyte evaporation to a level
that can damage the battery. It is best to use a low-current
charger
(6 amperes or less) to prevent battery damage
caused by overheating.
WARNING -
Hydrogen gas given off by the battery during charging is ex-
plosive. Do not smoke.
Keep open flames away from the top
ofthe batte~ and prevent electrical sparks by turning off the
battery charger before connecting or disconnecting it.
Battery electrolyte (sulfuric acid) can damage the car. If
electrolyte is spilled, clean the area with a solution
ofbak-
ing soda and water.
Always allow a frozen battery to thaw before attempting
to recharge it.
Always disconnect both battery cables and remove bat-
tery from vehicle during battery charging. Do not ex-
ceed
16.5 charging voltage at the battery
Battery safety terminal, replacing
If the battery safety terminal has been triggered, investigate
and correct the cause prior to replacement.
- Working in right side of luggage compartment, remove bat-
tery trim panel.
- Disconnect negative (-) battery terminal and cover with
insulator.
- Disconnect positive (+) cable from battery.
- Release positive (+) cable from cable brackets on luggage
compartment wall. Lay new repair cable parallel to positive
cable.
- Mark off length of new cable on old cable. Allow 10 cm
(2.5 in) of slack.
- Saw through old cable.
Do not use bolt cutters or similar tools to cut through cable.
A cable end that has been squashed
flat will not fit into the

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.- -
Fuel Tank and Fuel purnpl
Fuel pump power consumption, testing
To achieve accurate test results, the battery voltage at the
fuel pump connector should be
12.6 volts. Charge the battery
as necessary.
A higher than normal power consumption may indicate a
worn fuel pump, which may cause intermittent fuel starvation
due to pump overheating and seizure. The only remedy is
pump replacement.
A lower than normal power consumption
may indicate a blockage. Be sure to check that the return line
and the pump pickup are not obstructed before replacing the
pump.
- Expose right side access cover:
Peel forward lip of carpet.
Release rubber grommet from center of access cover insu-
lation.
Peel back insulation at perforations to expose fuel tank ac-
cess cover.
Remove right side cover to expose electrical harness con-
nector.
Disconnect harness connector from tank sending unit by slid-
ing lock back. Lift off connector.
Test fuel pump for current draw by attaching digital ammeter
between pump and harness (terminal
2, whitelblue wire) and
connect a jumper wire between pump and harness (terminal
1, brown wire) as shown.
CAUTION-
Do not allow the test leads to short to ground.
NOTE-
See 600 Electrical Systern-General for information on elec-
trical tests
using a digital multirneter.
Run pump as described in Operating fuel pump for tests.
- Compare ammeter reading with specification listed in ac-
companying table.
Fuel
pump current
Current consumption (average) 9.5 amps

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Warnings and cautions
Obse~e the following warnings and cautions when worlting
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 one hour), then release the
cap slowly to allow safe release ofpressure.
a Releasing the coolant system pressure lowers the cool-
ant boilingpoint and the coolant may boil suddenly. Use
1 heavy and wear eye and face protection to
guard against scalding.
Use extreme care when draining and disposing of en-
gine coolant. Coolant is poisonous and lethal to hu-
mans andpets. Pets are attracted to coolant because
of its sweet smell and taste. Seek medical attention im-
mediately if coolant is ingested.
CAUTIOG
Avoid adding cold water to the coolant while the engine is
hot or overheated. If it is necessary to add coolant to a
hol
system, do so only with the engine running and coolanl
pump turning.
To avoid excess silicate gel precipitation in the cooling
system and loss of cooling capacity, use BMW coolant
or equivalent low silicate antifreeze.
a If oil enters the cooling system, the radiator, expansion
tank and heating circuit must be flushed with cleaning
agent. BMW recommends removal of the radiator and
expansion
tank to flush.
When
worlcing on the cooling system, cover the alter-
nator to protect it against coolant drips.
Prior to disconnecting the battery, read the battery dis-
connection cautions given in
001 General Warnings
and Cautions.
Begin the diagnosis of cooling system problems with a thor-
ough visual inspection.
If no visual faults are found, it is rec-
ommend that the engine control module (ECM) fault memory
be checked for stored diagnostic trouble codes
(DTCs) using
BMW scan tool
DlSplus or equivalent.

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170-1 0
I Radiator and Cooling System
Combustion chamber leak test
- If you suspect that combustion chamber pressure is leaking
into the cooling system past the cylinder head gasket, use an
exhaust gas analyzer to test the vapors rising from the cool-
ant at the expansion tank.
CAUTIO&
Use an extension tube above the reservoir neclc to main-
tain distance between the top of the coolant and the gas
analyzer
nozzle. The gas analyzer is easily damaged if it is
allowed to inhale liquid coolant.
* While running engine to checlc for causes of overheat-
ing, observe coolant temperature carefully in order to
avoid engine damage.
Thermostat
If the engine overheats or runs too cool and no other cooling
system tests indicate trouble, the thermostat may be faulty.
In
V-8 models and 6-cvlinder models nroduced afler 911 998
(M52TU or M54 eng'ne), rheelecrricaily heated rhermostal IS
mon tored by [he OBD II diagnostlc software The fault may ic
in the DME software or hardware, or it may lie in the wiring to
the thermostat. See
OED On-Board Diagnostics.
Coolant, draining and filling
(6-cylinder models)
WARNING -
Allow the cooling system to cool before opening or draining
the cooling system.
- Raise front of car and support safely.
WARNING -
Make sure the car is stable and well supported at all times.
Use a professional automotive lift
orjack stands designed for
the purpose. A floor jack is not adequate support.
- Remove splash shield from under engine.
4 Loosen radiator bleed screw at top radiator fitting (arrow).
- Remove cap from radiator expansion tank. Set temperature
controls to
full warm.
gallon pail underneath radiator.

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Radiator and Cooling System
Cooling system, bleeding
Trapped air in the cooling system can prevent proper coolant
circulation and overheating. Wheneverthe coolant is drained
and filled, bleed the cooling system to remove trapped air.
4 Loosen bleed screw (arrow) on radiator expansion tank.
- Set temperature controls in passenger compartment to full
warm, set blower to low setting and turn ignition to
ON posi-
tion (do not start engine).
CAUTIOIG
On late model cars with latent heat pump, do not turn ignition
to ON position.
- Slowly add coolanUdistilled water mixture to expansion tank
until it spills from bleed screw. When coolant spilling from
bleed screws is free of air bubbles, tighten screw and replace
cap on expansion tank.
Run engine until it reaches operating temperature,
- After engine has cooled, recheck coolant level.
Top up so that coolant level indicator is at MAX.
- If trapped air cannot be bled manually, pressure-bleed sys-
tem using cooling system pressure tester.
CA UTlON--
Always use genuine BMW coolant or its equivalent to avoid
the formation of harmful, clogging deposits
in the cooling sys-
tem.
Tightening torque
Radiator bleed screw to radiator 2.5 Nm (22 in-lb)
Mechanical (viscous clutch) cooling fan,
removing and installing
The procedure given here describes the removal of the me-
chanical fan and fan shroud. It is possible to remove the fan
without the shroud.
< Working at top of fan shroud:
Remove expansion tank bleed screw (arrow) and expan-
sion tank locking tabs.
Push top of expansion
tank toward engine and lift to free
from lower mounts.
- Remove two expansion rivets in upper corners of fan shroud.
Unclip expansion tank bleed hose located under shroud.

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I Final Drive
4 Support inner hub with BMW special tools 26 1 110 and
press axle shaft out of joint using BMW special tool 21 2 120.
- Clean all old lubricant off shaft splines and inner joint splines.
If the CVjoint must be disassembled for cleaning and inspec-
tion, be sure to matchmark inner and outer race and interme-
diate ball cage. This allows reassembly
ofparfs in their
original positions.
NOTE-
To inspect a CVjoint, clean away the grease and loolc forgall-
ing, pitting, and other signs of wear orphysical damage. Pol-
ishedsurfaces or visible ball traclts alone are not necessarily
cause forreplacement. Discoloration due to overheating indi-
cates
laclt of lubrication.
- Slide CV joint boot onto axle shaft
- Apply LoctiteO270 or an equivalent heavy-duty loclting corn-
pound to drive axle splines. Position new CV joint on shaft so
that raised or taller side of hub is facing shaft.
WARNING-
Do not let the locking compound contact the balls in the joint.
Apply only a thin coat to cover the splines.
While supporting axle shaft with BMW special tool
33 2 130
press inner hub of CV joint onto shaft. Install a new circlip.
- Install new boot clamps.
- Use sealing gel to seal dust cover to CV joint prior to reinstal-
lation.
NOTE-
* Do not let the ball hub pivot too far in the outer ring of the
joint.
Tlie balls will fa1 out.
Before installing each small boot clamp be sure to
'burp"the
boot by flexing the CVjoint. A small screwdriver inserted be-
tween the boot and the axle shafl will help the process.
CV joint lubricant capacity
Wheel hub end
80 gram (2.8 oz)
Differential end
85 gram (3.0 oz)

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340-6
1 Brakes
Brake system troubleshooting
/symptom I Probable cause 1 Repairs
Brake squeal
Pedal goes to floor when
bralting
Low pedal after system bleeding
Pedal spongy or brakes work
only when pedal is pumped
Excessive braking effort
Brakes pulsate, chatter or grab
Uneven
bralting, car pulls to one
side, rear braltes
loclt
Brakes drag, bind or overheat Brake
pad carriers dirty or corroded or
pads loose (poor fit) in pad carrier
Braite pads heat-glazed or oil-soaked
Wheel bearings worn (noise most
pronounced when turning)
Incorrectly Installed brake pads,
parking bralte shoes, or bralte parts
Brake fluid loss due to system leaks
Master cylinder or traction control
system faulty
Master cylinder faulty
Air in braite fluid
Master cylinder or traction control
system faulty
Brake pads wet
Brake pads
heat-glazedorfluid-soalted
Vacuum booster or vacuum hose
connections to booster faulty
--- Warped brake rotors
Brake pads worn
Brake pads heat-glazed or oil-soaked Remove
brake pads and clean calipers. Use original
equipment pads for proper fit and use BMW anti-squeal
compound during installation,
Replace brake pads. Ciean rotors. Replace leaking caliper:
as required.
Replace worn bearings. See 310 Front Suspension
or33C
Rear Suspension.
Check component installation. Checldreplace anti-rattle
springs.
Checlt fluid level and inspect for signs of leakage.
Replace master cylinder. Diagnose traction control system
using factory or compatible diagnostic tool.
Replace master cylinder.
Bleed system using factory or compatible diagnostic tool.
Replace master cylinder. Diagnose traction control system
using factory or compatible diagnostic tool.
Use light pedal pressure to dry pads while driving.
Replace
bralte pads and rotors. Replace leaking calipers.
lnspect vacuum lines. Test vacuum booster and replace as
required. Test vacuum non-return valve for one-way flow.
Resurface or replace rotors.
Replace brake pads.
Clean rotors. Replace leaiting calipers.
Incorrect tire pressures or worn tires
Brake pads on one side of car heat-
glazed or fluid-soaked
Caliper or brake pads binding
Worn suspension components
Brake caliper or brake pads binding
Master cylinder or traction control
system faulty lnspect
tire condition. Checlt and correct tire pressures.
Replace brake pads. Clean rotors. Replace leaking
calipers.
Clean and recondition brakes.
Inspect for worn or damaged suspension components. See
310 Front Suspension or 330 Rear Suspension.
Ciean or replace caliper.
Replace master cylinder. Diagnose traction control system
using faclory or compatible diagnostic tool.

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340-1 5
Brakes
- Remainder of installation is reverse of removal.
- Clean brake caliper mounting bolts (7 mm Allen). Replace
ones which are not in perfect condition. Do not grease.
Top up brake fluid to MAX marking.
- Before driving car, pump bralte pedal several times so that
brake pads contact brake rotors.
Check that brake fluid level is correct. Top up if necessary.
Hold ignition key for at least
30 seconds in accessory po-
sition without starting engine. This clears any fault codes in
memory and turns off brake pad warning light.
Tightening torques Brake caliper to pad carrier
(7 mm Allen)
Front caliper
30 Nm (22 It-lb)
- Rear caliper 28 Nm (21 It-lb)
Road wheel to hub
120i 10 Nm (89i7 ft-lb)
Brake rotors, removing and installing
- Raise car and remove wheels
WARNING-
Male sure that the car is firmly supported on jack stands de-
signed for the purpose. Place jack stands beneath structural
chassis points. Do not place jack stands under suspension
parts.
Remove brake caliper carrier bolts (arrows). Suspend brake
caliper from chassis using stiff wire.
NOTE-
Hydraulic brake line remains connected.
4 Remove bralte rotor mounting screw (arrow) and remove ro-
tor.
- Inspect rotor for cracks, signs of overheating and scoring.
- Minimum allowable thickness (MIN TH) is stamped on rotor
hub. Measure rotor braking surface with a micrometer at
eight to ten different points and use the smallest measure-
ment. Compare to specifications in table below.
- If rotor does not pass minimum thickness requirements or is
damaged, replace rotor.

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Manual transmission
applications 200-2. 230-5
back-up light switch, replacing 230-6
gear ratios 230-6
gearshift
see Gearshiit
ID tag 200-2
fluid 020-1 0. 200-4 fluid service 230-6
oil seals
input shaft seal, replacing
230-17
output shalt seal, replacing 230-1 1
selector
shaft seal, replacing 230-8 pilot bearing 210-16
removallinstallation 230-19
see also Maintenance
Map light
see Lights, interior
Mass air flow
(MAF) sensor
see 130 under appropriate fuel
injection syslem
Master cylinder
see Brakes
see also Clutch, hydraulics
MDK
130-42
Microfilter see
NC, ventilation microfilter
see also Maintenance
Mirror see Exterior trim
Misfire see Ignition syslem, diagnosis
Motor mount
see Engine,
mounl
MRS (multiple restraint system)
see Airbag system (SRS)
Muffler
see Exhaust syslem
Neutral safety switch
see Automatic transmission, range
switch
OED II (on-board diagnostics)
OED-l
Oil change equipment 010-16
Oil level sensor
see Lubrication system
Oil pan
see Lubrication system
OH pressure
see Lubrication system
Oil pump
see Lubrication system
Oil service 020-1 1
On-Board Monitor
640-12
On-board diagnostics OED-1
Outside air temperature sensor
610-14
Outside door handle
see Door
loclc
Outside mirror switch
see Switches
Output
shaft oil seal
see Manual transmission, oil seals
Overheating
see Cooling system, troubleshooting
Overload protection
600-11
Oxygen sensors
130-72, 180-8
P codes OED-10
Panic mode operation
515-11
Parking brake
see Brakes
see also Maintenance
Parts, buying
010-11
Pedal cluster switches
see Switches
Pedal position sensor (PWG)
6-cvlinder
enqine
V-8 engine (M62 TU) 130-68
Pitman arm
see Steering
Power steering
see Steering
Power steering
fluid
see Maintenance
Power window switch
512-3 see also Switches
PWG see Pedal position sensor
(PWG)
Racic and pinion steering
see Steering
Radiator see Cooling system
Radiator cooling fan seeCooling system, cooling fan
see also Cooling system, electric fan
Radiator grill
see Exterior
trim
Radio
650-2 see also Antenna
see also Speakers
Rain sensor
611-6
Raising car safely
010-5
Readiness codes
OED-6
Rear door window
see Door window
Rear main seal
see Crankshalt oil seals
Rear parcel
sheif
513-16