Range Rover (LH) V8-3.5L (1987)
POSSIBLE CAUSES:
1)
No Fault - coolant is too hot or cold at operating temperature. Use a thermometer/pyrometer to confirm coolant temperature. The thermostat opens
at approximately 190 F but actual operating temperature may be somewhat higher or lower depending upon outside temperature, load etc.
2)
Out of tolerance voltage stabilizer in multifunction unit.
3)
Out of tolerance temperature sensor.
4)
Out of tolerance gauge unit.
5)
Poor wiring connections or poor grounds.
DIAGNOSTIC PROCEDURE:
1.
Remove green/blue wire from temperature sensor
2.
Switch on ignition.
3.
Connect an accurate voltmeter between the disconnected wire and ground. Specification: 10.0 +/- 0.25V
RESULTS:
1.
Correct voltage at this point indicated a properly operating voltage stabilizer. Pre adjust a 0-500 OHM variable resistor (available locally) with an
accurate ohmmeter to the values found on Table No. 1 and connect the resistor across the disconnected blue/green wire and ground. Allow at least
three (3) minutes for the gauge to stabilize at each setting.
TABLE 1
RESISTANCE VALUE
GAUGE NEEDLE POSITION
25 OHMS
-
Red Zone (overheat)
37 OHMS
-
High end of operating zone
80 OHMS
-
1/2 Scale
26 OHMS
-
Beginning of operating zone
Some variance between gauges is normal at each resistance value. Any large discrepancy indicates a defective gauge.
If the gauge checks O.K. with the variable resistor, use, a pyrometer/thermometer to record actual coolant temperature and measure the resistance of the
coolant temperature sensor (with the blue/green wire removed) with an ohmmeter. Compare the value you record with those on table No. 2.
TABLE 2
COOLANT TEMPERATURE
SENSOR RESISTANCE
130
F
-
182 OHMS
140
F
-
150 OHMS
150
F
-
125 OHMS
160
F
-
106 OHMS
170
F
-
93 OHMS
180
F
-
84 OHMS
190
F
-
79 OHMS
Replace any sensor which deviates from the values on table 2 by more than 10%.
Important:
make sure that the sensor threads are making good electrical contact with the intake manifold and that the engine to chassis ground is free of
resistance.
RESULTS:
2.
Incorrect voltage at the blue/green wire. Refer to troubleshooting procedure listed under "Complaint: no coolant gauge reading."