1997 GMC Sonoma Owner's Manual - Page 264

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