1995 GMC Yukon Owner's Manual - Page 259

I NOTICE: In cold weathbf, water can freeze and crack the engine, radiator, heater core and other parts. So use the recommended coolant. P 1. You can remove the coolant surge tankpressure cap when the cooling system, including the coolant surge tank pressure cap upper and radiator hose, is no longer hot. Turn the pressure cap slowly the left to until it first stops. (Don't press down while turningthe pressure cap.) If you hear a hiss, wait for to stop.A hiss means there is still some that pressure left. 5-21