I have a 1993 Ranger 2.3l 5-speed with 80,000 miles. I have been tryin to figure out an underheating problem, my truck runs about 160-170 normaly and gets about 16-18 mpg at best. I have tryed 3 thermostats, 2 stock 195 degrees and 1 special 205 degree with no help in warm up. I also put cardboard in front of the ac condenser plus an electric fan that turns on at 220 but it never gets that high(ran no fan at all in the summer with no over heat). truck still runs cold. hooked it up to a snap-on scan tool, had a slow responding o2 sensor, replaced it, no mileage increase. changed air filter, fuel filter, plugs, wires, belts, still no increase in mileage. after all that the scantool say the truck is running rich all the time, idel and driving. i tryed everything i can think of and nobody else seems to know anything either. can someone help me out?