How cold is it outside? Try covering the radiator with cardboard to get the temp up. The thermostats fail open so this could be the problem. The engine temps should be 190+. Mine is 170 to 180 and I have the replacement thermometer ready to go when I get a weather window to replace it in.
2006 F250 Lariat Supercrew, ESOF 4x4, 18" tires, FX 4, HD Alt., block heater, Integrated Trailer Brake Controller, Upfitters, power rear window, cab lights - delivered 10/25/05
Ford Remote Start; High idle mod; Timbren load levelers, Scangauge II, Blue Spring upgrade, Quick Start 200 amp large frame alternator replacement, 2 batteries; GPCM replace October 2011; 2 EGR valves; EGR Cooler replaced 12/30/11; Performance Machine & Mfg. coolant filter added 1/2/12; Rotella T6 5W40 oil; turned rotors and replaced brake pads for 1st time 1/7/12 101K miles; GPCM, both subharnesses and all 8 glowplugs replaced 1/5/13 at 118,000 miles; 2 Ford batteries replaced under battery warranty.