ok so you just put an additional fan on and didn't take the clutch one off. To gain the most mpg, Al is right you need to take it off and put just an electic. A friend of mine did that with his Tahoe and picked up 2 mpg just from that. And as far as the taking the Thermostate out, it won't cause you to over heat, but it can cause no heat in the winter. My thermostat was stuck open on my old 73 torino back in 2005 and I drove here to Washington DC with no heat because of the thermostat. It would get hot at low speed or just sitting there for like ever, but one I was going over 35 I lost the heat. Once I changed the thermostat, It worked again. So the lower temp thermostat and the electric fan is the best more for hp and mpg.