Thermostat Diagnosis
THERMOSTAT INSPECTION AND TESTINGUse the following procedure in order to do an operational test of the thermostat:
1. Drain the coolant to a level just below the thermostat. Refer to Draining and Filling Cooling System.
2. Remove the coolant outlet. Refer to the appropriate procedure: Radiator Hose Replacement.
3. Remove the thermostat. Refer to the appropriate procedure: Thermostat Replacement.
4. Unless the thermostat is obviously faulty, test the thermostat before replacing the thermostat using the following procedure:
4.1. Place the thermostat and a thermometer in a container with a 50/50 solution of water and ethylene glycol antifreeze.
IMPORTANT: While heating, do not rest the thermostat or the thermometer on the bottom of the container. This causes the thermostat and the thermometer to be at a higher temperature than the solution.
4.2. Place the container over a heater.
4.3. Agitate the solution in order to maintain a uniform temperature of the solution, the thermostat, and the thermometer. The thermostat valve should start to open at the rated temperature. The thermostat should be fully open after the temperature has increased 15°C (27°F).
A used thermostat can be about 6°C (10°F) above or below these settings without adversely affecting the thermostat and you do not need to replace the thermostat. If the thermostat does not operate at the temperatures specified, replace the thermostat. You cannot adjust the thermostat.
FAN NOISE
Fan noise is sometimes evident under the following conditions:
^ When the clutch is engaged for maximum cooling.
^ During the first 15 seconds to one minute after start-up until the clutch can redistribute the silicone fluid back to the fluid's normal disengaged operating condition (after overnight settling).
Fan noise, or an excessive roar, generally occurs continuously under all high engine speed conditions (2500 RPM and up) it the clutch assembly is locked up because of an internal failure. If the fan cannot be rotated by hand, or if there is a rough grating feel as the fan is turned, replace the clutch. Refer to the appropriate procedure:
^ Fan Clutch Replacement.
LOOSENESS
Inspect a loose fan clutch assembly for wear. Replace the fan clutch as necessary.
Under various temperature conditions, a lateral movement is visible at the tip of the fan blade. About 6.5 mm (1/4 inch) maximum lateral movement, measured at the fan tip, is allowable. Replacement of the fan clutch is not necessary.
Ensure that the fan blade is installed properly. If the fan is installed incorrectly, the fan will cause an overheating problem.
SILICONE FLUID LEAKS
Small fluid leaks, occurring in the area around the bearing assembly, do not affect the operation of the fan blade clutch.
If leakage appears excessive, replace the fan blade clutch. Refer to the appropriate procedure:
^ Fan Clutch Replacement.
ENGINE OVERHEATING
1. In order to ensure complete fan blade clutch disengagement, begin testing with a cool engine.
2. If the fan blade clutch assembly revolves more than 5 times when spun by hand, replace the fan blade clutch. Refer to the appropriate procedure:
^ Fan Clutch Replacement.
3. If the clutch performs properly with a slight drag, refer to step 3. Testing a fan blade clutch by holding the small hub with one hand, and rotating the aluminum housing in a clockwise/counterclockwise motion, causes the clutch to "free wheel." Consider this operation normal and this test should not determine replacement.
4. Position a thermometer between the fan blades and the radiator. Do this by inserting the thermometer sensor through one of the existing holes in the fan shroud, or by placing the thermometer between the radiator and the fan shroud. On some models, you may have to drill a 5 mm (3/16 inch) hole in the fan shroud in order to insert the thermometer.
5. With the thermometer in position, perform the following steps:
5.1. Sufficiently cover the radiator grille in order to induce a high engine temperature.
5.2. Start the engine.
5.3. Turn on the A/C.
5.4. Operate the engine at 2000 RPM.
6. Inspect the thermometer reading when the clutch engages. Allow approximately 5-10 minutes for the temperature to become high enough to engage the fan blade clutch. This will be indicated by an increase, or roar, in fan air noise and by a drop in the thermometer reading of about 3 - 10°C (5 - 15°F).
^ If the clutch did not engage between 65 - 90°C (150 - 195°F), replace the assembly. Ensure that the fan blade clutch was disengaged at the beginning of the test.
^ If you observed no sharp increase in fan noise or temperature drop, and the fan noise level was constantly high from the start of the test to 88°C (190°F), replace the assembly. Do not continue this test past a thermometer reading of 88°C (190°F) in order to prevent engine overheating.
7. When the clutch engages, perform the following steps:
7.1. Remove the radiator grille cover.
7.2. Turn off the A/C in order to assist in Cooling System.
7.3. Operate the engine at about 1500 RPM.
8. After several minutes, the fan blade clutch should disengage as indicated by a reduction in fan speed and roar. If the fan blade clutch fails to function as described, replace the fan blade clutch.