GMC CHEVROLET Silverado 1500 2021 Owner's Manual page 337

336 Vehicle Care
Check to see if coolant is visible in the
coolant surge tank. If the coolant inside the
coolant surge tank is boiling, wait until it
cools down. The coolant level should be at
or above the indicated mark. If it is not,
there may be a leak in the cooling system.
If coolant is visible but the coolant level is
not at or above the indicated mark, see the
following sections on how to add coolant to
the coolant surge tank following.
Automatic Coolant Service Fill
Instructions (L3B Engine)
This feature assists in filling and removing
air from the cooling system after service of
components or when coolant is added after
being too low.
To activate the fill and air removal process:
1. Remove the coolant surge tank pressure
cap when the cooling system, including
the coolant surge tank pressure cap and
upper radiator hose, is no longer hot.
Turn the pressure cap; slowly
counterclockwise about one full turn. If a
hiss is heard, wait for that to stop.
A hiss means there is still some
pressure left.
2. Keep turning the pressure cap slowly,
and remove it.
3. Fill the coolant surge tank with the
proper mixture to the indicated mark.
4. Connect the vehicle to a battery charger.
5. Set the ignition to service mode, see
Ignition Positions (Keyless Access) 0 230
or
Ignition Positions (Key Access) 0 229.
6. Turn off the air conditioning.
7. Set the parking brake.
8. At the same time, press the accelerator
and the brake for automatic vehicles for
two seconds, then release.
9. Listen for pump activation and
movement of the control valves while
watching the level of the coolant in the
surge tank. Add fluid as the level drops
below the indicated mark on the surge
tank. Allow 15 minutes for the fill and air
removal process to complete.
10. Reinstall the surge tank cap.
If the tank empties, turn the ignition off,
allow the Electronic Control Module (ECM) to
go to sleep, about two minutes, refill to the
indicated mark, and repeat Steps 5 9.
How to Add Coolant to the Coolant
Surge Tank for Gasoline Engines
Except L3B
If the vehicle has a diesel engine, see
Cooling System in the Duramax diesel
supplement for the proper coolant fill
procedure.
Warning
Spilling coolant on hot engine parts can
burn you. Coolant contains ethylene
glycol and it will burn if the engine parts
are hot enough.
Warning
Plain water, or other liquids such as
alcohol, can boil before the proper
coolant mixture will. With plain water or
the wrong mixture, the engine could get
too hot but there would not be an
overheat warning. The engine could catch
fire and you or others could be burned.