2003 GMC Sonoma Owner's Manual - Page 291

What to Use Use a mixture of one-half clean, drinkable water and one-half DEX-COOL@coolant which won't damage aluminum parts. If you use this coolant mixture, you don't need to add anything else. Nofice: If you use an improper coolant mixture, your engine could overheat and be badly damaged. The repair cost wouldn't be covered by your warranty. Too muchwater in the mixture canfreeze and crack the engine, radiator, heater core and other parts. If you have to add coolant more than four times a year, have your dealer check your cooling system. Adding only plain wa-- 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 50/50mixture of clean, drinkable water and the proper coolant. Notice: If you use the proper coolant, you don't have to add extra inhibitors or additives which claim to improve the system.These can be harmful. 5-28