Pontiac 2003 Aztek Owner's Manual page 325

Notice: When adding coolant, it is important that
you use only DEX-COOL@ (silicate-free) coolant.
If coolant other than DEX-COOL is added to
the system, premature engine, heater core or
radiator corrosion may result. In addition, the engine
coolant will require change sooner
-
at 30,000 miles
(50 000 km) or 24 months, whichever occurs first.
Damage caused by the use of coolant other
than DEX-COOL@ is not covered by your new vehicle
warranty.
How to Add Coolant to the Coolant
Recovery Tank
If you haven't found a problem yet, but the coolant level
isn't at or above the FULL COLD mark, add a
50/50 mixture of clean, drinkable water and DEX-COOL@
engine coolant at the coolant recovery tank. See
Engine Coolant on page 5-22 for more information.
Adding only plain water to your cooling
system can be dangerous. Plain water, or
some other liquid such as alcohol, can boil
before the proper coolant mixture will. Your
vehicle's coolant warning system is set for the
proper coolant mixture. With plain water or the
wrong mixture, your engine could get too hot
but you wouldn't get the overheat warning.
Your engine could catch fire and you or others
could be burned. Use a 50/50 mixture of clean,
drinkable water and DEX COOL@ coolant.
Notice: 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.
5-30