I measured the temp sensor on the water bridge that sends inputs to the gauge on my 82 5 speed. I have been told that when hot (above 104F) the sensor should read 100 -160 ohms. The sensor reads only half that at 57 ohms.

The engine has less than 1000 miles on a full rebuild, radiator is only a few years old, new water pump, fairly new thermostat and new 3000 cfm electric puller fan set up.

If the sensor resistance is indeed low, would this cause a high reading on the temp gauge and does it need replaced? When fully warm, the temp gauge reads about two needles width below the second white line. It was

The actual IR temps when warm are about 175F at the inlet of the radiator and about 15F less at the water bridge. About 150F coming out of the radiator, so I don't think it is actually getting hot.

Any thoughts?

 

Try shorting the gauge wires at the sender and see what happens at the gauge - should peg I think. Or pull the sender and measure its resistance in boiling water - that will give you something concrete, unless you are at a significant altitude. The gauge reading sounds normal, depending on the ambient temp. My electric fan switch (in the top hose) closes at 98C, opens 93C (208F/199F), and the gauge peaks just below the second white line.
jp 83 Euro S AT 55k