Top sensor with one wire - your gauge indicator that essentially
measures engine head temperature.
The bottom sensor - a VERY important issue! It is the computer's
engine coolant temperature sensor. Its the one with two wires. THIS
item only costs about $9 at AutoZone, but IT is responsible for half of
the Saturns you'd see in the junkyard.
This sensor goes bad, then the engine computer runs too rich, the fan
motor won't switch on and the car develops chronic overheating problems
(because the computer thinks the engine is very cold WHEN it's very
HOT.)
When this sensor goes bad, the car will not pass an emissions test and
will idle at about 1200 while stopped and 1700 rpm while car is moving.
At about 60degrees w/engine cold, the sensor should measure about 4k
ohms resistance. At 200degrees (engine hot) the sensor measures about
100 ohms.
Its hard to check this sensor while its in the engine... I made my own
connector from a cable harness from a dead tv set (little inline plug
inserts).
I just bought my second SC2. I got a GREAT deal on it was because the
original owner's "shade tree" mechanic didnt know what was going on
with it. As I'd had experience with this sensor problem with my first
Saturn - I realized when I test-drove it exactly what was going on!
This applies to SC and SL Saturns from 91 to at least 96.
