Chevrolet Low Cab Forward 4500 2019 Series Owner's Manual page 202

The radiator cap (1) opens and
closes in double action. When
removing the radiator cap, take
caution not to damage the cap and
the filler neck (2).
Turn the cap slowly to the left until it
reaches a stop . Do not press down
while turning the cap.
Wait until any remaining pressure
(indicated by a hissing sound) is
relieved, then press down on the
cap and continue turning it to
the left.
Also, check to make sure there are
no leaks from the radiator or
radiator hose. Check for fluid or
stains on the ground showing leaks
where the vehicle is parked. Contact
your dealer if you discover leaks.
Using the vehicle when there are
leaks can lead to engine seizure.
Adding Engine Coolant
Single Cab Model
Vehicle Care
Crew Cab Model
When the engine coolant level in the
engine coolant reserve tank is
below the MIN line, open the
reserve tank cap and fill to near the
MAX line with engine coolant.
Wash the reserve tank cap and filler
neck with clean water. Tighten the
cap securely after the engine
coolant has been replenished.
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