There is no problem mixing regular coolant and DEX-Cool. You just have to change it as often as using just regular coolant. I'm using DEX-Cool in 1st3L95 since it was filled up again. It's real easy to totally flush out the green coolant completely if you have a pressurized flush machine. But seeing I have a brand new block and rebuilt heads, I just flushed the radiator and heater core out with water, then filled the whole sucker up with DEX-Cool.
PranQster - Sounds like you have a head gasket problem.
