<<I aim it at the night sky and it reads -58F!!.>>

Max....my friend...Your IR gun needs to reflect off of something, and that is why is it reading -58F just pointing at the night sky...it is either very confused...or it is reading the moon ;)
(In which case, that is one heck of an IR gun for just $65!)

You are totally right though, readings on a hose, for instance, will be a bit lower than the coolant inside due to the insulation properties of the rubber. But you can use these things for all types of stuff on your engine that lack the insulative (spelling?? I'm terrible) properties of rubber and such, including readings on oil temp from the pan, head temps, etc. 

Like you say, it is somewhat comparative...but so is the stock VDO gauge since there really isn't a true temperature called "middle" or "just above the LED."

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