Temp acting up after radiator replacement

Jake21

Jake21

TJ Enthusiast
Joined
Feb 19, 2021
Messages
110
Location
Santa Fe, NM
Hey Guys,
I had the radiator on the 2000 4.0 replaced last week. The temp gauge is showing pretty cool (like 180ish maybe) for a fairly long time upon the first trip of the day and will eventually get up to 210. Yesterday after about an hour on the highway, I noticed the temp was a bit over 210. the needle was covering up the 0.

Does this sound like a thermostat going bad?

TIA.
JJ
 
That temperature sounds fine but it sounds like they screwed up and didn't install the correct 195 degree thermostat. Probably a 165 or 180 degree thermostat which is not the correct temperature. It should warm up quickly and go right to 210 or close to it.
 
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Jerry Bransford said:
That temperature sounds fine but it sounds like they screwed up and didn't install the correct 195 degree thermostat. Probably a 165 or 180 degree thermostat which is not the correct temperature. It should warm up quickly and go right to 210 or close to it.
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Ah ha! Just looked at the receipt. shows a 160. thanks!
 
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Jake21 said:
Ah ha! Just looked at the receipt. shows a 160. thanks!
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Make sure the replacement 195 degree thermostat is NOT a "fail-safe" model. While fail-safe sounds good fail-safe thermostats actually like to fail way too easily in the open position which defeats its purpose. They won't usually fail in the problem-causing closed position but they fail often enough in the open position that I wouldn't run one.
 
Jerry Bransford said:
Make sure the replacement 195 degree thermostat is NOT a "fail-safe" model. While fail-safe sounds good fail-safe thermostats actually like to fail way too easily in the open position which defeats its purpose. They won't usually fail in the problem-causing closed position but they fail often enough in the open position that I wouldn't run one.
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cool. thx
 
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With the 160 thermostat installed, why would the temp get past 210 when it was 90 degrees outside? Shouldn't it have been closer to 160?
 
Jake21 said:
With the 160 thermostat installed, why would the temp get past 210 when it was 90 degrees outside? Shouldn't it have been closer to 160?
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Thermostats open when the temp reaches the setpoint and that's it. It's only job is to set minimum operating temperatures. Put 6 Jeeps in 100 deg desert temps with 6 different thermostats and they will ultimately all run at similar temps,
 
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Jake21 said:
With the 160 thermostat installed, why would the temp get past 210 when it was 90 degrees outside? Shouldn't it have been closer to 160?
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No, a thermostat doesn't have the ability to affect the engine temperature in warm or hot conditions. Its only job is to help the engine warm up faster and to help set a minimum operating temperature when the ambient air temperature is cool or cold. If you could lower an engine's temperature in warm or hot conditions by just running a 160 or 180 degree thermostat we wouldn't need our big radiators.

If you're in warm to hot conditions the engine will still run at or near 210 degrees whether the thermostat is a 160, 180, or 195 degree model thermostat.
 
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