2003 GMC Sonoma Owner's Manual - Page 290

How to Check and Add Fluid The proper fluid should be added if the level does not reach the bottom of the diaphragm when it's in place in the reservoir. See the instructions on the reservoir cap. A 50/50 mixture of clean, drinkable water and DEX-COOL@ coolant will: Give freezing protection down to -34°F (-37°C). Give boiling protection up tcz 265°F (-129°C). Protect against rust and corrosion. Help keep the proper engine temperature. 0 Engine Coolant The cooling system in your vehicle is filled with DEX-COOL@ engine coolant. This coolant is designed to remain in your vehicle for 5 years or 150,000 miles (240 000 km), whichever occurs first, if you add only DEX-COOL@extended life coolant. The following explains your cooling system and how to add coolant when it is low. If you have a problem with engine overheating, see Engine Overheating on page 5-30. Let the warning lights and gages work as they should. Notices When adding coolant, it is important that (silicate-free) coolant. you use onlyDEX-COOL@ 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 30,000miles -(50,000 km) or 24 months, whichever occurs first. Damage caused by the useof coolant other than DEX-COOL@is not covered by your new vehicle warranty. 5-27