1993 Pontiac Bonneville Owner's Manual - Page 240

What to Use: Use a mixture of one-half clean water 'preferably distilled) and one-half intifreeze that meets "GM Specification 1825-M," which won't damage aluminum parts. You can also use a recycled coolant conforming to GM Specification 1825-M with a complete 2oolant flush and refill. If you use this mixture, you don't need to add anything 1 se. : Adding only plain water to your cooling system can be wgerous. Plain water, or some other liquid like alcohol, can boil :forethe proper coolant mix will. Your vehicle's coolant warning system is set for the proper coolant mix. With plain water or the wrong mix, your engine couId get t o hot but you wouldn't get the o overheat warning. Your engine could catch fire and you or others could be burned. Use a S0/50 mix of clean water and a proper antifreeze. If you use an improper coolant mix, your engine could overheat and be badly damaged. The repair cost wouldn't be covered by your warranty. Too much water in the mix can freeze and crack the engine, radiator, heater core other parts.