2000 chevy venture overheating and low coolant light on when coolant is full

There is a heat sensor located near the thermostat that goes directly into the block. Get a Haynes or Chiltons manual.

The thermostat is probably bad and causing your overheating. If that is not hte problem, then it would probably be your water pump.

Low coolant could be cause by a leak somewhere in the the system. I had to have my manifold intake gasket replaced to stop the leak. For now, what I would suggest doing, is just replace the coolant with DEXcool, and always keep it at the line in the coolant area. If, with the coolant full, your van is still overheating, it could either be your water pump (but you would hear a chirping or cricket noise) or it could be your harmonic balancer going (you would also notice that you're going through belts often, or that your belt is a little damaged)