BMW 1989-1995 525i Service Manual page 207

Thermostat Quick Check
RADIATOR AND COOLING SYSTEM
170-3
To check if the thermostat is opening and coo lant is circ ulat-
ing through the radiator. allow a cold engine to reach ope rat-
ing temperature (temperature gauge need le approximately
centered). Feel the top radiator hose. If the hose is hot to the
touch. the coolant is probably circulating correctly. If there are
any cool areas in the hose or radiator . coolant flow to the radi-
ator is probably restricted. Check for a faulty thermostat or a
plugged radiator.
NOTE -
A thermostat that is stuck open will cause the engine to
warm up slowly and run below norma l tempe rature at
highway speed. A thermostat that is stuck closed will re-
strict coolant flow to the radiator and cause overheating.
If the engine overheats and no other coo ling system tests
indicate trouble. the radiator may have some plugged passag-
es that are restricting coolant flow.
Temperature Gauge Quick Check
A quick. easy test at the coolant temperature gauge sender
can determ ine if the gauge is functioning co rrectly.
If the gauge needle rema ins at the rest po sition with the en-
gine warm , disconnect the connector from the sending unit
and jumper the two terminals in the connector to simulate a
high engine temperature. See Fig. 2. Turn the ignition on. If
the gauge needle moves upward. the send ing unit is faulty. If
the gauge does not respond. the wiring to the gauge is broken
(open circuit) or the gauge itself is faulty.
Fig . 2. Temperature gauge sender (brown bod y) on M50 engine.
t o-
cation of sender varies depending on eng ine type.
Temperature gauge sender location
• Brown switch body
525i (M20 engine) in therm ostat housing
535i (M30 engine) in therm ostat housing
525i (M50 engine) front of cyl. head. intake side
530i . 540i (M60 engine) rear of engine.
in coola nt manifold
NOTE -
On
MBO
engines. remove the top engme cover to
ac-
cess the gauge sender in the coots nt manifold at the
rear 01the engine.
If the gauge needle reads too high when the engine is cold.
disconnect the connector from the sender. Turn the ignition
on. If the gauge needle position does not cha nge. the wiring or
the gauge is shorted to ground . If the gauge needle drop s. the
sender is faulty and should be replaced. When replaci ng a
faulty coolant temperature sender . the gasket ring on the
sender should also be replaced.
Tightening Torque
• Temperatur e gauge sender 18 Nm ( t 3 tt-lb)
Cooling Fans Quick Check
An otherwise sound cooling system may still overheat. par-
ticularly with prolonged idling . due to a failure of the prima ry
cooling fan. The cooling fan is controlled by a temperature de-
pend ent viscous fan clutch. A failed fan clutch may affect air
flow through the radiator resulting in overheating or possibly
over cooling.
Inspect the fan clutch by spinning the fan with the engine off
and cold. The viscous fan should spin on the clutc h with slight
resistance . Check for signs of leaking fluid from the clutc h. If
the fan freew heels with little resistance. cannot be turned by
hand. or there are signs of oil leakag e. the clutch should be re-
placed.
WARNING-
• Use caution when testing the cooling Ian and
cootent temperature switches. Keep hands and
wires clear 01 the Ian btades. TIle coaling fan can
run any time the ignitIon is ON.
• For greatest safely. cooling fan and cootent tem-
perature switch tests should be performed on
a
cold engine with the air conditioning off.
The auxiliary (electric) cooling fan provides add itional air
flow through the radiator when coolan t temperature exceeds
a predetermined level or whenever the air conditioning is on.
The fan assembly is mounted in front of the radiator. A dual-
range temperature switch is mount ed on the right side of the
radiator.
TROUBLESHOOTING