GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Engine 🢒 Engine Cooling 🢒 Loss of Coolant

Step

Action

Yes

No

DEFINITION: The cooling system is loosing coolant either internally or externally.

1

Were you sent here from Symptoms or another diagnostic table?

Go to Step 2

Go to Symptoms - Engine Cooling

2

Repair any present DTCs. Refer to Diagnostic Starting Point - Engine Cooling .

Is the action complete?

Go to Step 3

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3

Inspect the coolant level.

Is the coolant at the proper level?

Go to Step 6

Go to Step 4

4

Fill the cooling system to the proper level. Refer to Cooling System Draining and Filling .

Is the action complete?

Go to Step 5

--

5

If the engine is suspected to have a coolant leak into the cylinder, the coolant can hydraulically lock the cylinder.

Does the engine crankshaft rotate?

Go to Step 6

Go to Step 28

6

Engine overheating can cause a loss of coolant.

Is the engine overheating?

Go to Step 29

Go to Step 7

7

Extended engine operation with a low coolant level can cause engine internal component failure.

Is the engine knocking?

Go to Step 31

Go to Step 8

8
  1. Idle the engine at normal operating temperature.
  2. Inspect for heavy white smoke coming out of the exhaust pipe.

Is a heavy white smoke present from the exhaust pipe?

Go to Step 9

Go to Step 10

9
    • Coolant in the exhaust system creates a distinctive, burning coolant odor in the exhaust.
    • Condensation in the exhaust system can cause an odorless white smoke during engine warm up.

Does the white smoke have a burning coolant type odor?

Go to Step 30

Go to Step 10

10

With the engine idling, inspect the coolant recovery system.

Does the coolant recovery system discharge coolant while the engine is idling?

Go to Step 15

Go to Step 11

11

Visually inspect the hoses, pipes and hose clamps at the following locations:

    • Auxiliary heater
    • Coolant bypass
    • Surge tank
    • Hot water shut-off valve
    • Radiator

Are any of the hoses, clamps or pipes leaking?

Go to Step 21

Go to Step 12

12

Visually inspect the following components:

    • Block heater
    • Coolant pressure cap
    • Core plugs
    • Cylinder head gaskets
    • Engine block
    • Hot water shut-off valve
    • Intake manifold
    • Radiator
    • Thermostat
    • Water pump
    • Fuel injector sleeve

Are any of the listed components leaking?

Go to Step 21

Go to Step 13

13
  1. Pressure test the cooling system. Refer to Cooling System Leak Testing .
  2. Visually inspect the components listed in steps 11 and 12 again.

Are any leaks present?

Go to Step 21

Go to Step 14

14

Pressure test the coolant pressure cap. Refer to Pressure Cap Testing .

Does the coolant pressure cap hold pressure?

Go to Step 16

Go to Step 22

15

Pressure test the coolant pressure cap. Refer to Pressure Cap Testing .

Does the coolant pressure cap hold pressure?

Go to Step 32

Go to Step 22

16

Inspect for the following conditions:

    • A coolant smell inside of the vehicle
    • Coolant in the HVAC module drain tube
    • Coolant on the vehicles floor covering under the HVAC module

Is coolant present?

Go to Step 23

Go to Step 17

17

If equipped with auxiliary heating, inspect for the following:

    • A coolant smell inside of the vehicle
    • Coolant in the auxiliary HVAC module drain tube
    • Coolant on the floor covering near the auxiliary HVAC module

Is coolant present?

Go to Step 24

Go to Step 18

18

Inspect the underside of the oil fill cap for a gray/white milky substance.

Is there a milky substance under the oil fill cap?

Go to Step 19

Go to Step 20

19

Inspect the engine oil fluid level indicator for a gray/white milky substance.

Is there a milky substance on the engine oil fluid level indicator?

Go to Step 30

Go to Step 20

20

Inspect the automatic transmission oil fluid level indicator, if equipped, for a gray/white milky substance.

Is there a milky substance on the automatic transmission fluid level indicator?

Go to Step 25

Go to Step 33

21

Repair or replace the leaking component. Refer to the appropriate repair.

Is the repair complete?

Go to Step 33

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22

Replace the coolant pressure cap.

Is the repair complete?

Go to Step 33

--

23

Replace the heater core. Refer to Heater Core Replacement in Heating, Ventilation and Air Conditioning.

Is the repair complete?

Go to Step 33

--

24

Replace the auxiliary heater core. Refer to Auxiliary Heater Core Replacement in Heating, Ventilation and Air Conditioning.

Is the repair complete?

Go to Step 33

--

25
  1. Remove the transmission oil cooler lines from the radiator.
  2. Pressure test the cooling system. Refer to Cooling System Leak Testing .
  3. Inspect the transmission oil cooler for coolant.

Is coolant present in the transmission oil cooler?

Go to Step 26

Go to Step 27

26
  1. Replace the radiator. Refer to Radiator Replacement .
  2. Service the automatic transmission.

Is the repair complete?

Go to Step 33

--

27

Install the cooler lines to the radiator.

Is the action complete?

Go to Step 33

--

28

Repair the engine no crank condition. Refer to one of the following procedures:

    •  Engine Will Not Crank - Crankshaft Will Not Rotate in Engine Mechanical - 8.1L
    •  Engine Will Not Crank - Crankshaft Will Not Rotate in Engine Mechanical - 6.6L (LB7)
    •  Engine Will Not Crank - Crankshaft Will Not Rotate in Engine Mechanical - 6.6L (LLY)

Is the repair complete?

Go to Step 33

--

29

Repair the engine overheating condition. Refer to Engine Overheating .

Is the repair complete?

Go to Step 33

--

30

Repair the engine internal coolant leak. Refer to one of the following procedures:

    •  Coolant in Combustion Chamber in Engine Mechanical - 6.6L (LB7)
    •  Coolant in Combustion Chamber in Engine Mechanical - 6.6L (LLY)
    •  Coolant in Combustion Chamber in Engine Mechanical - 8.1L

Is the repair complete?

Go to Step 33

--

31

Repair the engine knock. Refer to one of the following procedures:

    •  Lower Engine Noise, Regardless of Engine Speed in Engine Mechanical - 6.6L (LB7)
    •  Lower Engine Noise, Regardless of Engine Speed in Engine Mechanical - 6.6L (LLY)
    •  Lower Engine Noise, Regardless of Engine Speed in Engine Mechanical - 8.1L

Is the repair complete?

Go to Step 33

--

32

Repair the combustion pressure in the cooling system problem. Refer to one of the following procedures:

    •  Lower Engine Noise, Regardless of Engine Speed in Engine Mechanical - 6.6L (LB7)
    •  Lower Engine Noise, Regardless of Engine Speed in Engine Mechanical - 6.6L (LLY)
    •  Lower Engine Noise, Regardless of Engine Speed in Engine Mechanical - 8.1L

Is the repair complete?

Go to Step 33

--

33

Operate the system in order to verify the repair.

Did you find and correct the condition?

System OK

Go to Step 2