Hyundai Sonata Hybrid 2021 Owner's Manual page 414

Emergency situations
WARNING
Never remove the engine
coolant cap and/or inverter
coolant cap or the drain plug
while the engine and radiator
are hot.
Hot coolant and steam may blow out
under pressure, causing serious injury.
Turn the hybrid system off and wait until
the engine cools down. Use extreme
care when removing the engine coolant
cap and/or inverter coolant cap. Wrap
a thick towel around it, and turn it
counterclockwise slowly to the first
stop. Step back while the pressure is
released from the cooling system. When
you are sure all the pressure has been
released, press down on the cap, using
a thick towel, and continue turning
counterclockwise to remove it.
7-8
CAUTION
• Serious loss of coolant indicates a
leak in the cooling system and should
be checked as soon as possible by an
authorized HYUNDAI dealer.
• When the engine overheats from
low engine coolant, suddenly adding
engine coolant may cause cracks
in the engine. To prevent damage,
add engine coolant slowly in small
quantities.