GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2003 🢒 Yukon XL - 2WD 🢒 Engine 🢒 Engine Controls - 4.8L, 5.3L, and 6.0L 🢒 Loss of Coolant

Step

Action

Yes

No

1

Were you sent here from Symptoms, or another diagnostic table?

Go to Step 2

Go to Symptoms - Engine Cooling

2

Inspect the coolant level.

Is the coolant at the proper level?

Go to Step 4

Go to Step 3

3

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

Is the action complete?

Go to Step 4

--

4

Engine overheating can cause a loss of coolant.

Is the engine overheating?

Go to Step 18

Go to Step 5

5
  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 6

Go to Step 7

6

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 19

Go to Step 7

7

Visually inspect the hoses, pipes and hose clamps.

Are any of the hoses, clamps or pipes leaking?

Go to Step 20

Go to Step 8

8

Visually inspect the following components:

    • Block heater
    • Coolant pressure cap
    • Core plugs
    • Throttle Body
    • Engine block
    • Intake manifold
    • Radiator
    • Thermostat housing
    • Water pump

Are any of the listed components leaking?

Go to Step 20

Go to Step 9

9
  1. Pressure test the cooling system. Refer to Cooling System Leak Testing .
  2. With the cooling system pressurized, visually inspect the components listed in steps 7 and 8.

Are any leaks present?

Go to Step 20

Go to Step 10

10

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

Does the coolant pressure cap hold pressure?

Go to Step 11

Go to Step 15

11

Inspect for the following conditions:

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

Is coolant present?

Go to Step 20

Go to Step 12

12

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

Is there a milky substance under the oil fill cap?

Go to Step 13

Go to Step 14

13

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 16

Go to Step 14

14

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 17

Go to Step 21

15

Replace the coolant pressure cap.

Is the repair complete?

Go to Step 21

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16
  1. Replace the radiator. Refer to Radiator Replacement .
  2. Service the engine oil and filter. Refer to Engine Oil and Oil Filter Replacement in Engine Mechanical - 4.8L, 5.3L, and 6.0L or to Engine Oil and Oil Filter Replacement in Engine Mechanical - 8.1L.

Is the repair complete?

Go to Step 21

--

17
  1. Replace the radiator. Refer to Radiator Replacement .
  2. Service the automatic transmission. Refer to Engine Coolant/Water in Transmission in Automatic Transmission.

Is the repair complete?

Go to Step 21

--

18

Repair the engine overheating condition. Refer to Engine Overheating .

Is the repair complete?

Go to Step 21

--

19

Repair the engine internal coolant leak. Refer to Coolant in Combustion Chamber and Coolant in Engine Oil in Engine Mechanical - 4.8L, 5.3L, and 6.0L or to Coolant in Combustion Chamber and Coolant in Engine Oil in Engine Mechanical - 8.1L.

Is the repair complete?

Go to Step 21

--

20

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

Is the repair complete?

Go to Step 21

--

21

Operate the system in order to verify the repair.

Does the system operate correctly?

System OK

Go to Step 2