AVI ASE-A8, Руководство пользователя, Страница: 27 / 130

Chapter A: General Diagnosis
21
System Pressure Test
Pressure testing the cooling system is a quick and easy
way to find an external leak. Perform the test on a cold
engine using a hand pump with a gauge:
1. Remove the pressure cap and attach the pressure
tester to the filler neck.
2. Pump the tester until the gauge reading matches
the specified system pressure, figure 1-24.
3. Observe the gauge; the reading should remain
steady.
4. If the gauge shows a pressure loss, pump the tester
to maintain pressure and check for leaks.
Radiator Cap Pressure Test
Check the radiator pressure cap using the system pres-
sure tester and an adapter:
1. Attach the cap to the pressure tester.
2. Pump the tester until the gauge reading matches
the pressure rating of the cap.
3. Observe the gauge; it should hold steady within one
or two psi of the rating for at least 10 seconds, then
gradually decrease.
4. If the reading does not drop at all, continue apply-
ing pressure until the cap vents. The cap should
vent when pressure exceeds the rating by one to
three pounds. Replace the cap if it fails either test.
Thermostat Service
A thermostat that opens above or below its temperature
rating will cause driveability problems. If the thermostat
is stuck open, or there is no thermostat installed in the
system, the engine may never reach an efficient operat-
ing temperature. In many instances, the thermostat is
defective and should be replaced. Thermostat function
can be checked on a running engine. Refer to Book A1
"Engine Repair" in this series for more detailed informa-
tion on thermostat testing.
Fan Clutch Operation Test
A thermometer and an ignition timing light can be used
to check the operation of a viscous fan clutch. You must
know the temperature setting of the drive unit. To test:
1. Attach a thermometer to the engine side of the ra-
diator. Be sure it will clear the fan blades and be
visible with the engine running.
2. Connect the timing light and start the engine. Note
the thermometer reading on a cold engine.
3. Aim the timing light at the fan blades; they should
appear to move slowly.
4. Block the radiator to reduce air flow and raise tem-
perature. Do not allow the engine to overheat.
5. Continue watching the thermometer and keep the
timing light on the fan blades.
6. When the thermometer reaches the clutch engage-
ment point, fan speed should increase. The blades
will appear to move faster in the timing light beam.
7. Unblock the radiator so that the temperature drops.
If the system is working properly, fan speed will de-
crease when the temperature is below the engage-
ment point of the clutch.
Electric Coolant Fan
Electric coolant fans, which are designed to operate
only when necessary, figure 1-25. Several methods are
used to control fan operation:
Fig. 1-23. Testing engine coolant with a hydrometer.
Fig. 1-24. Pressure testing the cooling system.