Is pouring out coolant after driving for 10 minutes?

Help! I have this wonderful van, well almost wonderful, that is pouring out coolant after driving for 10 minutes, if that. We have changed the water pump, twice in a years time, but it is still not wanting to do right. In 2005, we had to put a new thermostat sensor in because of the coolant smell. That stopped the problem, temporarily. Now the temperature gage inside the van is going haywire!
It will start out on cold and within two minutes of driving, it will jump to hot and then drop to normal then back to hot. We have bleed the lines, done all that we know to do, but it is still not fixing the problem.
We are also having a problem with the air flow from the vents. I can turn the air on to 5 and it feels like it is on one. Could there be something stopping up the lines to keep the air from flowing thru the vents and could this be related to the coolant problem? Both of these problems started about the same time. Thank you!