It has only been going to about 60 but today it went up to 70 or so. It was warmer today so I didn't need the heater, but I tried it and it really pumped out the hot air. A bad thermostat would also explain the worse mileage in colder weather. Thanks, I guess I'll get a new thermostat and put it in, I'm going to flush the system and put new antifreeze in while I'm at it.

__________________
1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k