GMC Yukon Denalid Owner's Manual page 452

The coolant level should be at or above the
FULL COLD mark. If it is not, you may have
a leak at the pressure cap or in the radiator
hoses, heater hoses, radiator, water pump, or
somewhere else in the cooling system.
452
CAUTION:
{
Heater and radiator hoses, and other
engine parts, can be very hot. Do not
touch them. If you do, you can be burned.
Do not run the engine if there is a leak.
If you run the engine, it could lose all
coolant. That could cause an engine fire,
and you could be burned. Get any leak
fixed before you drive the vehicle.