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We've had complaints of overheating on some late model GM truck engines; any clue why this is happening?

If you rebuild model year 2003 GM 4.8L, 5.3L or 6.0L VIN V, T and U truck engines, your customers may be unaware of new GM coolant fill procedures. The following is good information to duplicate and include with a rebuilt engine.

Following this procedure will ensure that the engine coolant system has been filled properly.

Improper coolant filling may occur following a condition where the engine coolant has been drained. If the cooling system is filled through the radiator neck and/or engine coolant overflow reservoir engine, overheating may result. When attempting to fill that way the engine coolant may not flow beyond the closed thermostat located on the lower engine at the radiator hose connection. The engine coolant level may appear to be full up to the radiator neck when actually the system may be 4-6 quarts low. If the engine is operated that way an engine overheating condition may occur.

GM offers the following information to correctly fill the cooling system on these engines.

1. Reposition hose clamp and remove the upper radiator hose.
2. Remove the coolant air bleed hose from the radiator.
3. Use a 50/50 mixture of DEX-COOL® antifreeze or equivalent and deionized water.
4. Slowly fill the cooling system through the upper radiator hose with 50/50 coolant mixture until the coolant comes out the coolant air bleed hose.
5. Connect the upper radiator hose to the radiator.
6. Install the upper radiator hose and reposition the clamp to the original position on the hose.
7. Connect the coolant air bleed hose to the radiator.
8. Fill the coolant overflow bottle to the full line.
9. Start engine and run at 2000-2500 rpm until the engine reaches normal operating temperature.
10. Allow engine to idle for 3 minutes.
11. Shut the engine off and allow to cool, top off coolant as necessary.
12. Check coolant for correct concentration.
13. Rinse away any excess coolant from the engine compartment.
14. Inspect cooling system for leaks.

NOTE: Tools required to do the procedure properly are J26568 coolant & battery tester and a J38185 hose clamp pliers.

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