Engine will not warm up over about 163 degrees

2004 CHEVROLET IMPALA
154,000 MILES • 3.4L • 6 CYL • 2WD • AUTOMATIC
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BRYANPH
  • MEMBER
  • 3 POSTS
Changed thermostat and coolant temperature sensor. used 180 degree thermostat. temperature gauge only reads 160 degrees. used hand held laser temperature reader on the water hoses and they to only read about 163 degrees. as it idles it will warm up more and the laser temperature check reflects that as will. once you start moving it will then cool back down to about 160'. this is also causing the check engine light to trigger as will. what is keeping it from warming up to full operating temperature?
Apr 28, 2020 at 10:25 AM
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ASEMASTER6371
  • ✓Experienced Mechanic
  • 52,796 POSTS
Good afternoon,

The car requires a 195 degree thermostat for the system. The 180 is incorrect and must be replaced.

https://www.2carpros.com/articles/replace-thermostat

The reason for the light is the coolant temperature sensor is sending a cold reading to the ECM for more time that is allowed. Without it being at the correct temperature it will set a P0128 code for low engine temperature.

https://www.2carpros.com/articles/how-a-coolant-temperature-sensor-works

Do not use a thermostat that has overheat protection.

Roy
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Apr 29, 2020 at 5:11 AM
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BRYANPH
  • MEMBER
  • 3 POSTS
thanks for your reply. So I went out and replaced the thermostat again and put in a 195 degree thermostat. The engine light immediately went out and the temperature came up. But it still only runs about 170 degrees. I remember this car did always run cool. So I ask. with a 195 degree thermostat the thermostat should be wide open at that temperature, what should the average temperature be?
May 3, 2020 at 5:27 AM
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ASEMASTER6371
  • ✓Experienced Mechanic
  • 52,796 POSTS
The thermostat starts to open at 170 and is fully open at 200.

Running at 170 is a good normal temperature.

https://www.2carpros.com/articles/how-an-engine-thermostat-works

170-180 is average.

Roy
May 3, 2020 at 5:35 AM
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BRYANPH
  • MEMBER
  • 3 POSTS
Okay, sounds good. that would explain a lot. Thanks for your help. Problem fixed.
May 3, 2020 at 8:21 AM
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ASEMASTER6371
  • ✓Experienced Mechanic
  • 52,796 POSTS
You are welcome.

Always glad to help.

Roy
May 3, 2020 at 8:25 AM
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