1998 GMC Sonoma Owner's Manual - Page 277

Checking Coolant Turning the radiator pressure cap when the engine and radiator are hot can allow steam and you badly. scalding liquids to blow out and burn With the coolant recovery tank, will almost you never have to add coolant at the radiator. Never turn the radiator pressure cap even a little when the engine and radiator are hot. -- -- Add coolant mixture at the recovery tank, but be careful not to spill it. When your engine is cold, the coolantlevel should be at ADD, or a little higher. When your engine is warm, the level should be LIP to FULL HOT, or a little higher. Adding Coolant c If you need more coolant, add the proper DEX-COOL@ coolant mixture ut the coolant recovery tank. You can be burned if you spill coolant on hot engine parts. Coolant contains ethylene glycol, and it will burn if the engine parts are hot enough. Don't spill coolant on a hot engine. 6-27