You're correct in assuming that the rubber hose temp would be something
less than the temp of the coolant flowing through it.
  The directions on my gun said that the surface that you aim it at has a
certain return reflectivity based on smooth/ rough, dull/shiny, black/
silver, etc. that will cause a certain amount of reading error.
  I just figure that I'm not looking for absolute accuracy, just comparative
readings.
  I was able to find a poorly-running cylinder using this comparative
concept.  When I fixed the problem, the engine ran smoother, and the
different temps evened out accordingly.
  I was very impressed and consider this IR gun a valuable tool in my
arsenal.

Mike B.

>Although these readings are to the extreme ends of
the scale, I have often wondered how accurate the readings are in automotive
usage.  If you aim the beam at a radiator hose, I'm sure it's giving you an
accurate reading on the rubber hose temp. but wouldn't the coolant inside
the hose be even hotter(at operating temperature anyway)?