1996 GMC Savana Van Owner's Manual - Page 207

8. Then replace the pressure cap. At any time during this procedure if coolant begins to flow out of the filler neck, reinstall the pressure cap. Be sure the arrows on the pressure cap line up like this. - Under heavy vehicle loading, trailertowing andor high outside temperatures, the fan speed increases as the clutch more fully engages. So you may hear an increase in fan noise. This is normal and should not be mistaken as the transmission slipping or making extra shifts. It is merely the cooling system functioning properly. The fan will slow down when additional cooling is not required and the clutch partially disengages. You may also hear this fan noise when you start the engine. It will go away as the fan clutch partially disengages. 5-19