2005 Pontiac GTO Owner's Manual - Page 211

Adding Coolant If you need more coolant, add the proper DEX-COOL® coolant mixture at the coolant overflow reservoir, but be careful not to spill it. Check the level with the dipstick and keep adding fluid until the level is correct. {CAUTION: 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. The coolant level should be checked at each fuel fill, by looking at the dipstick in the coolant overflow reservoir. To remove the dipstick, push down on the coolant reservoir cap while turning it counterclockwise. When your engine is cold, the coolant level should be at or above the bottom arrow on the dipstick. After the vehicle has been driven and the engine is at normal operating temperature, the level should be somewhere between the two arrows on the dipstick. If the coolant level is correct, replace the dipstick then push down on the coolant reservoir cap while turning it clockwise until it stops, to lock it into position. When the level is correct, replace the dipstick then push down on the coolant reservoir cap while turning it clockwise until it stops, to lock it into position. 5-25