1993 GMC Suburban Owner's Manual - Page 245

If theoverheatwarningcontinues, there's onemore thing you can try. You can addthepropercoolantmixdirectly to theradiator,but be surethe radiator is cool before you do it. Steam and scaldingliquidsfromahotcoolingsystem can blow out and burn you badly.Theyareunderpressure,and if you turnthe radiatorpressure cap-even alittle-theycancome out at high speed.Never turn thecapwhenthecoolingsystem,includingthe radiatorpressurecap,ishot. Wait for the cooling system andradiator pressurecaptocool if youeverhave to turnthepressure cap. 1. You can removetheradiatorpressure cap whenthe cooling system, including the radiatorpressurecapandupperradiatorhose is nolonger hot. Turnthepressurecapslowly to the left until it firststops. (Don't press down while turning thepressurecap.) If you hearahiss,waitforthat pressureleft. to stop. A hissmeansthere is still some 5-1 3