1993 Buick Roadmaster Owner's Manual - Page 224

How to Add Coolantto the Radiator . i=. : . i i i t -c 2. Then keep turning the pressure cap, but now push downas you turn it. Remove the. pressure cap. -: , :.c,- , I. . . . I -" . -..- ' . . . . ., I 1. You can remove the radiator pressure cap when the cooling system, including the radiator pressure cap and upper radiatorhose, is no longer hot. Turn the to pressure cap slowly the left until it first stops. (Don't press down while turning pressure cap.) the If you hear a hiss, wait for that to stop.A hiss means there is still some pressure left. 3. Fill the. radiator with the proper mix, up to the base of the filler neck.