1995 GMC Sonoma Owner's Manual - Page 240

I NOTICE: If you use an improper coolant mix, your engine could overheat and be badly damaged. The repair cost wouldn't covered by be mix your warranty. Too much water in the can freeze and crack the engine, radiator, heater core and other parts. Some conditions, such as air trapped in the cooling system, can affect the coolant level in the radiator. Check the coolant level when the engine is cold and follow the steps under "Adding Coolant'' for the proper way to add coolant. If you have to add coolant more than four times a year, have your dealer check your cooling system. NOTICE: If you use the proper coolant, don't have to add extra you inhibitors or additives which claim to improve the system. These can be harmful. Adding Coolant 6-22