Dodge D150 1990 Service Manual page 295

7 - 6 COOLING SYSTEM •
COOLING SYSTEM D I A G N O S I S - C O N T I N U E D
CONDITION AND CHECKS DIAGNOSIS
TEMPERATURE GAUGE IS INCONSISTENT, CYCLES AND/OR IS
ERRATIC.
(1) Is cycle normal.
(a) Normal Gauge Reaction to Thermostat Cycle.
A /
1-X \
MID
(b) Normal Gauge Reaction at Stop After Heavy Use.
(c) Hot Water Build-Up is Normal at Stop after Heavy Use.
(2) Is coolant in radiator low (air will build up in the cooling system (2) Fill system, vent trapped air and check for leaks.
and cause the thermostat to open late).
(3) Is a cylinder head gasket leak allowing exhaust gas to enter
(3) a — Test for leaking cylinder head gasket leak with a
cooling system (exhaust gas building up in the cooling system will commercially available Block Leak Tester.
cause the thermostat to open late).
b — Check for coolant in engine oil.
c — Inspect for white steam from exhaust system.
(4) Water pump impeller loose on shaft. Loose accessory drive belt. (4) Repair or replace as necessary.
(5) Air leak on the suction side of the water pump (allows air to build (5) Find leak and repair.
up in cooling system causing thermostat to open late).
WARNING UGHT GLOWS ALL THE TIME (VEHICLE NOT
EQUIPPED WITH GAUGE).
(1) Inspect temperature gauge sending unit. The warning light sending (1) Ensure that a warning light sending unit is installed.
unit has a screwdriver slot in the electrode (used for calibration).
Gauge sending units do not have a slot in the electrode.
NO GAUGE READING INITIALLY THEN HOT INDICATION
(VEHICLE EQUIPPED WITH GAUGE).
(1) Gauge stationary until very hot, then moves immediately to "H".
(1) Vehicle is equipped with sending unit for light not gauge.
J9007-70