Dude I got the perfect solution for you I have an 03 4.0 and I had a coolant leak near the thermostat and it looked like the housing. IT WASN'T it was a 25 cent o ring on the temp sensors I replaced the thermo housing and replaced the gaskets started the truck and it still leaked. Now I looked closer the temp sensors had leaked by the little o rings which fill the valley and simmer coolant giving you the smell of burning coolant and no obvious leak point. Lastly the o rings on the sensors didn't look that bad cracked split or otherwise but that was the leak replaced the o rings a d it hasn't leaked for 10k plus miles
2003 XLT Ranger 4.0 5 Spd manual
Mods: New 4.0, 3 inch superlift kit, custom mounted 8000lb warn winch, 4.11 gears, one off traction bar, KC slimlite daylighters x4, fords traction-lok posi w/ revised friction ordering, centerforce stage 1 clutch, 17 inch rims w/ 33" Bfg KM2's, JBA firecone headers, single chamber flowmaster, full 2 1/2" exhaust, Superchips flashpaq tuner, K&N 77 series cold air intake, Demon coil pack, uniden cb radio, leather tonneau cover and still waiting for more.