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Discussion Starter #1
I have a 94 caprice classic ls with an LT1, recently after an optispark and water pump change I had my scanner hooked up while driving back and forth to work. I noticed the coolant temp was 205.4 degrees while cruising 55 to 60 mph. The needle on the dash gauge seemed normal , just below half way. Well after two days of driving and making sure all the air was out of the system I decided to go ahead and replace the thermostat. The old one was maybe two years old 180 degrees and I replaced it with another of the same temp. I tested both in a pan of water and they both performed the same. I put the new one in and blead the system of air over another two days. Now while cruising the pcm says 207 degrees. So my question is, is that the normal operating temp ?
 

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Yes,valthough a few degrees higher than some. It may be time to have your radiator rodded out. You might fill out the rest of your profile so we have some idea of the ambient temps where you are driving. No one here is going to come knock on your door if that is why you haven't done so.
 

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The pcm reads the coolant temp at the H2Opump, whereas the dash temp gauge reads the temp between cylinders 6 & 8.

A significant difference between the H2Opump temp sensor & the dash temp gauge indicates one or both of two things:
1. The engine's been working [or playing] unusually hard in the past 5 minutes
2. the radiator, H2Opump, and/or radiator fans are no longer cooling as well as they should.

If either the H2Opump temp sensor [and]or the dash temp gauge ever indicate 239°F, there's something seriously wrong.
If in doubt, paying attention to the hotter of the two readings will nearly always save your heads from warping [which is why the dash temp gauge exists in the 1st place].
Scott Mueller said:
B- & D-car coolant fans operate under PCM control at the following H2Opump temperatures and A/C system pressures:

Fan ……………… Mode …… Temps ……… A/C Pressure
Primary (RH)…ON…… 109°C / 229°F……189 psi
Primary (RH)…OFF……105°C / 221°F……150 psi
2ndary (LH)……ON…… 112°C / 234°F……240 psi
2ndary (LH)……OFF……108°C / 227°F……210 psi

Additionally, the PCM will turn off the fans at higher vehicle speeds (above 48 MPH I believe), since running fans can actually impede airflow through the radiator at high speed.
Each fan also has a minimum running time. Once activated, the primary fan will run for a minimum of 50 seconds, and the secondary fan for a minimum of 26 seconds.
Finally, certain Diagnostic Trouble Codes (DTCs) may cause the PCM to turn on one or both fans.
Settling for the OEM fan-on thresholds is HIGHLY inadvisable, completely unnecessary, and potentially costly.
Even if one were to install an aftermarket 195°F thermostat, the fan-on thresholds can STILL be lowered to 213°F & 222°F.
With the OEM 180°F thermostat, the fan-on thresholds should be 203°F & 212°F.

Frankly, the number of people who continue to settle for OEM fan thresholds is baffling.
 

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Discussion Starter #5 (Edited)
No one here is going to come knock on your door if that is why you haven't done so.

I found it amusing that (FBI)9c1 wrote that. Anyway, I live about 50 miles southwest of chicago. With the old thermostat running 205 degrees the ambient temp was about 55 in the morning and 70 in the afternoon. With the new thermostat running 207 it was about 60 in the morning and 80 in the afternoon. I changed the reservoir cap yesterday and today in the morning it was 45 I was running 206 and this afternoon 72 and running 208.
 

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As marky suggested "With the OEM 180°F thermostat, the fan-on thresholds should be 203°F & 212°F." is about right. Those of us in warmer climates in many cases like a 160 Stat with even lower fan turn on temps and running temp.
That being said, a 180 stat is fully open around 195 and it seems to me that highway crusing in those ambient temps should be a few degrees lower than the 207'ish numbers you are getting. I wouldn't be concerned a lot about it, but it might be that your cooling system isn't flowing at the optimal rate. Maybe a system flush or radiator rodding out would be a good idea at some future time. Good luck!
 

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Discussion Starter #7
About three years ago I put in a new radiator, say 30000 miles ago. at that time I flushed the cooling system real good and I mean real good. Heater core seems to be flowing good, last week I put in brand new heater hoses and restricter from GM and replaced the egr valve, optispark ,plug wires ,water pump, air conditioning compressor , power steering pump. The air pump was removed about three years ago also. Car has 140,000 now and I have never driven it in the winter.
 
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