2002 Oldsmobile Silhouette

Engine Cooling problem
2002 Oldsmobile Silhouette 6 cyl Front Wheel Drive Automatic 126000 miles

im having a problem with my van. When I decelerate it overheats but when I accelerate mos of the time it cools down to normal and my heat comes out hot again. I dont have any antifreeze in my oil nor do I ven lose any antifreeze.I have been trying to figure it out. Got it working fine for about a week and it started doing it agani. Ive replaced the thermostat and flushed radiator. Any ideas?
October 18, 2010.

Seems like either there is a clog in the system (heater core etc.) Or radiator fans may not be working properly

Oct 18, 2010.