I think he means Thermometer :)

   Get the engine up to operating temp (or pretty close) with the radiator cap off.
 Don't rev the engine, or you'll get wet.  When the dash gauge gets to 140*, stick a
thermometer in there and see what you get.

   If the gauge is reading low, that could be a problem.  If the computer thinks
it's still cold, it will run rich and you'll waste fuel, burn out the cats, and foul
the plugs.   How to check the computer, you ask?  I don't know.