Buick 2014 Regal Owner's Manual page 267

If no problem is found, check to see
if coolant is visible in the coolant
surge tank. If coolant is visible but
the coolant level is not at the
indicated level mark, add a 50/
50 mixture of clean, drinkable water
and DEX-COOL coolant at the
coolant surge tank, but be sure the
cooling system, including the
coolant surge tank pressure cap, is
cool before you do it.
Steam and scalding liquids from a
hot cooling system can blow out
and burn you badly. Never turn
the cap when the cooling system,
including the surge tank pressure
cap, is hot. Wait for the cooling
system and surge tank pressure
cap to cool.
In cold weather, water can freeze
and crack the engine, radiator,
heater core, and other parts. Use
the recommended coolant and
the proper coolant mixture.
You can be burned if you spill
coolant on hot engine parts.
Coolant contains ethylene glycol
and it will burn if the engine parts
are hot enough. Do not spill
coolant on a hot engine.
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-quarter of a turn. If you hear
a hiss, wait for that to stop. This
will allow any pressure still left to
be vented out the
discharge hose.
2. Keep turning the pressure cap
slowly and remove it.