1998 GMC Suburban Owner's Manual - Page 271

6. Start the engine and let it run until you can feel the upper radiator hose getting hot. Watch out for the engine cooling fan(s). 7. By this time, the coolant level inside the r*d' d lator filler neck may be lower. I f the level is lower, add more of the proper DEX-COOL@ coolant mixture through the filler neck until the level reaches the base of the filler neck. 8. Then replace the pressure cap. At any time during this procedure if coolant begins to flow out of the filler neck, reillstall the pressure cap. Be sure the arrows on the pressure cap line up like this. 5-21