No Heat and Overheating in 1999 Chevy Silverado

After replacing the thermostat, you must bleed the air from the cooling system.

To bleed air from the 2.2L and 2.5L engines, remove the plug or sensor on the top of the thermostat housing. Fill the radiator with coolant until the coolant comes out the hole. Since the plug is made out of steel and the thermostat housing is aluminum, it is a good idea to apply an anti-seizing compound or Teflon® tape on the plug threads prior to installation. Install the plug and continue to fill the radiator. This will vent all trapped air from the engine.

Any trapped air in the heating system will have to be displaced by coolant. Once the cooling system is filled, with the radiator cap off, turn of the heater at it's highest setting. Start the engine and allow it to reach operating temp. You should see a drop in the coolant level as the air in the heating system is displaced by coolant. Add coolant to the proper level and replace the radiator cap.

Keep a close eye on the coolant level for at least the next couple of weeks. The cooling system is a "closed" system. Any significant decrease in coolant level indicates a problem.

If you have any questions, let me know.

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Drive safe and be warm.

clarkco

Hi on thoes trucks the theermostat must be put in with the little hole in the thermostat pointing at 12 oclock or pointing away from radiator to let all air out.and check for a colapsing hose stpoing the coolant from circulating. tyr that first