I assume that your 93 RS has the same 3.2L SOHC engine as does my 95 S model.
My temperature gauge practically never moves, regardless of temp, load, wind direction or A/C on/off. I just drove the vehicle from PA to Moab to coastal Oregon pulling a >3100lb trailer--the temp gauge barely rose pulling over the rockies west of Denver or driving straight into 40mph winds in 4th gear at 70mph/4K rpm with the A/C on for an entire tank of gas.
I do have the shield you refer to, but would be amazed if the lack of that shield would cause wild swings in coolant temp--it might be exactly that, but I'd be surprised.
Definitely a strange set of symptoms. If it's an automatic, perhaps the tranny fluid is getting overheated at highway speeds and some of that heat is transferring from the tranny cooler to the radiator. Or maybe you've got some sort of fan/water pump problem at higher RPMs.
In any case, that shield should be cheap even if you have to order it from a dealer. A junkyard shield should be less than $10, I'd think.
-------------------- 1995 Trooper S
Bone Stock, for now...
It's better to regret something you did
Than something you didn't do
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