Cooling system question

I had/have a problem with my cooling system (1993 SC-2, 105K) in that my
temperature gauge all of a sudden started to do 2 strange things:

1. Run hot (over 3/4) or cool (under 1/4), seemingly connected to driving
conditions (hot when I was running the AC or climbing a grade on a hot day,
cool when coasting with good airflow through the radiator)
2. Wander around quite a bit, going back and forth around a centerpoint that
was probably the right temperature

Until very recently, my temperature gauge used to be rock solid, just above
or just below the 1/2 way point in all driving conditions once the engine
warmed up. I do know that my radiator fan used to kick on reliably when just
above 1/2, and turn off reliably when the temp reached just below 1/2.

I took the car into my mechanic, who replaced 2 coolant temp sensors, which
cured problem #2. However, problem #1 remains, even after taking the car
back to the mechanic a second time and describing the issue.

After the second time, the mechanic said there was no problem that he could
see. The radiator fan was kicking in at 220 (as read several places by an
infrared sensor), at which point the temp gauge was at 3/4, and turning off
at 195, or 1/2 on the temp gauge. He told me I shouldn't worry about it
unless the temp gauge got into the red.

So, a few questions:
1. Why would both these issues (1 and 2 above) happen at the same time, and
only #2 get fixed by new coolant temp sensors?
2. Why does the Saturn have 2 coolant temp sensors and where are they
located in case I want to replace them again myself? How hard is that to do?
3. Could the new coolant temp sensors he put in be calibrated differently
from my originals such that the normal operating range is now just below 1/2
to just above 3/4 instead of just below 1/2 to just above 1/2?
4. Is there anything else I should be looking for, and should I be worried
about driving around with the temp gauge at 3/4?

 

It's likely that the old temperature sensor didn't properly reflect the
coolant temperature swings with any sensitivity and so appeared the temp
was staying closer to 1/2 at all times. Proper operation is to heat the
coolant to what shows as approx. 1/2. The fan will kick on at
approximately 3/4 and stay on until the temp falls below 1/2. In hot
weather, especially stop and go driving the temp could maintain at
approximately 3/4, so I wouldn't worry about driving in those
circumstances. I WOULD however if the radiator fan was not cutting on
at the specified point. Since your mechanic already advised it is. I
wouldn't be worried.

The saturn has two coolant temp sensors; I'm not 100% sure but I believe
one is dedicated to operation of the car (in calculating timing,
fuel/air mix, etc.) while the other is purely for the indicator gauge on
your dash.

If you want to replace them they are not THAT hard, but there is a lot
of part removal and twisting of arms to get it done. The process is
described in a Haynes or Chilton's.

Hope I helped.

Bob

 

Bob,

This was very helpful. Thanks for the advice. I guess the temp gauge was
actually not working to spec the entire 12 years I've owned this car
previously.

Thanks

 

No problem. It turned out the original temp sensor on my 1992 SL2 was
the same way. Of course I waited until it was out of warranty to get it
fixed...