Un less there is air flow through the heater core it wont do much cooling.
In my ZX2SR, the Zetec thermostat had an O ring that fitted around the stat. without it the stat would not seal allowing some by pass. Just a thought.
Normally, the fan is only effective in slow driving. Ram air at highway speeds does the cooling.
Warm the engine up while observing with the heat gun to see if it agrees with the computer. It will at least tell you what the offset is between the two sensors. Watch it go down after it opens and verify that the tow agree. Having the two temp sensors (computer and IR thermometer) agree will give you a degree of confidence moving forward.
If the computer and the IR gun agree, pull the t-stat and drive the thing. It should never warm up. My thoughts are that the T-stat is not closing after it opens for some reason.
I like the idea of blocking off the rad also as you will be able to observe any increase with your two independent temperature sensors. Be a good time to add some degree of calibration to that dash gauge that you don't trust: you say it reads somewhere in the middle, now you can put a temp value to that position.
Yall maybe onto something about the heater core bypass. Iirc lots of todays cars use a bypass so the heater producd heat before the tstat opens. My vote is a malfuncioning bypass valve
Fairly common problem. I'm going to bet you have a messed up heater core control valve. They fail with regularity on those trucks. I know mine was replaced twice in the time I owned my ranger.
Thanks again for all the input.
I probably won't have a chance to dig into any of this until the weekend, but I will report the results back when I can get out there and try a few of these things.
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