1996 GMC Sonoma Owner's Manual - Page 248

NOTICE: If you use an improper coolant mix, your engine could overheat and be badly damaged. The repair cost wouldn't be coveredby your warranty. Too much water in the can freeze mix and crack the engine, radiator, heater core and other parts. If you have to add coolant more than four timesa year, have your dealer check your cooling system. Checking Coolant NOTICE: If you use the proper coolant, you don't have to add extra inhibitors or additives which claim to improve thesystem. These can be harmful. When your engine is cold, the coolant level should be at ADD, or a little higher. When your engine iswarm, the level should be up to FULL HOT, or a little higher. 6-26,