i had a verry similar problem in my 96 with the 2.3. i replaced the thermostat the sender and still it appeared to run cold so i fiddled around the circut board with inback of the guage cluster with my multi meter and found that the stepping motor that was showing engine tempreture had too much resistance, probably from years of use. i know if you'r reall good with a solder gun you can replace the stepping motor but otherwize as long as it produses hot air in the winter i dont think it'll affect much besides the angle of the needle

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96 xlt 2.3l 4cyl extended cab 2wd 5 speed no mods yet