For 1990-2009 cars

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Inspect for a loss of system pressure. Is there a loss of system pressure? | -- | Go to Step 2 | Go to Step 3
2 | Inspect and repair any faulty hose connections. Does the engine still overheat? | -- | Go to Step 3 | System OK
3 | Inspect for low coolant protection (-37°C/-34°F). Is low coolant protection present? | -37°C (-34°F) | Go to Step 4 | Go to Step 5
4 | Replace the coolant. Refer to Cooling System Draining and Filling . Does the engine still overheat? | -- | Go to Step 5 | System OK
5 | Inspect the drive belt for excessive wear or low tension. Is the drive belt worn or is the tension too low? | -- | Go to Step 6 | Go to Step 7
6 | Replace the drive belt. Refer to Drive Belt Replacement in Engine Mechanical - 8.1L. Does the engine still overheat? | -- | Go to Step 7 | System OK
7 | Inspect the water pump. Is the water pump inoperative? | -- | Go to Step 8 | Go to Step 9
8 | Replace the water pump. Refer to one of the following procedures:

• | Water Pump Replacement for 8.1L

• | Caterpillar® 3126 Unit Repair Manual

Does the engine still overheat?

--

Go to Step 9

System OK

9 | Inspect the radiator fins for obstruction. Are the radiator fins obstructed? | -- | Go to Step 10 | Go to Step 11
10 | Inspect and clean the radiator. Refer to Radiator Cleaning . Does the engine still overheat? | -- | Go to Step 11 | System OK
11 | Inspect the cooling system passage for obstruction. Is the cooling system passage blocked? | -- | Go to Step 12 | Go to Step 13
12 | Inspect and flush the system. Refer to Flushing . Does the engine still overheat? | -- | Go to Step 13 | System OK
13 | Inspect the fan clutch. Refer to Fan Clutch Diagnosis . Is the fan clutch inoperative? | -- | Go to Step 14 | Go to Step 15
14 | Replace the fan clutch. Refer to Fan Clutch Replacement . Does the engine still overheat? | -- | Go to Step 15 | System OK
15 | Inspect for a stuck thermostat. Refer to Thermostat Diagnosis . Is the thermostat stuck in the closed position? | -- | Go to Step 16 | Go to Step 17
16 | Replace the thermostat. Refer to one of the following procedures:

• | Engine Coolant Thermostat Replacement for 8.1L

• | Caterpillar® 3126 Unit Repair Manual

Does the engine still overheat?

--

Go to Step 17

System OK

17 | The following factors may cause the engine to overheat:

• | A heavy vehicle payload

• | Excess engine oil

• | Restricted air flow through the radiator

• | Extreme air temperature

Correct or repair as necessary.

Does the engine still overheat?

--

--

System OK