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2002 Chevy Trailblazer LT
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Discussion Starter #1
So I have an 02 TB 150k miles. Recently the temperature gauge has been fluctuating. When I start the car the temp usually goes all the way up to a tick below 210 then while diving it will fluctuate all the way down To 155. I can’t find any leaks from my 3 month old radiator and even when the temp dips all the way down to 155 I have the heat on and it still runs really hot and never changes . So I makes me think it’s not the thermostat. Would it be coolant sensor or water pump? Any tips would be appreciated.
 

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Chevy Trailblazer 2008 LTZ (4.2L)
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105 Posts
Do you have a cheap OBD2 scanner and torque app on your smartphone?
See if the temperature really drops when the arrow on the dashboard goes down.
Let me know when you check it out.
 

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2002 Chevy Trailblazer LT
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Discussion Starter #3
The upper radiator hose was original and had a small drip, I replaced that hose and tightened the clamp. It seems to be helping it still fluctuates but seems to be way more stable now and for the most part after its hot . The needle sits a tick below 210. It drops down every once in awhile but not that much. I’m going to get a good Obd2 scanner like you suggest. I have a feeling it could be my stepper motors going bad I get a few clicks in dash
 

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Chevy Trailblazer 2008 LTZ (4.2L)
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Yes, unfortunately, the failure of stepper motors on the dashboard is a common problem.
Check the temperature with a scanner.
 

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2002 Chevy Trailblazer LT
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Discussion Starter #5
So I got the OBDLinkmx+ and when the needle dips the temp goes down to about 170. But once I drove it for about 25 min it seemed the readings I was getting was between 175 and 190. When cruising and idling when I got home it was at about 185. Should I worry about it or would this be about normal?
 

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2002 chevy trailblazer_lt
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174 Posts
If anything that sounds a bit low. I normally see 206 at fully warmed up highway and drifting upwards of 212 when idling afterwards.
 

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2002 Chevy Trailblazer LT
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Discussion Starter #7
Throttle body was cleaned last month, It’s a new radiator, vvt solenoid, spark plugs and coils have 20k miles on them. Can’t really slow the fan down at all and so the fan clutch seems good. And I’m noticing any leaks or play in water pump either. It seems to be driving pretty nice.
 

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2002 chevy trailblazer_lt
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174 Posts
I would not say it is low enough to cause a concern, just maybe a notch lower than average.
 

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Chevy Trailblazer 2008 LTZ (4.2L)
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I think there is no reason for concern, a slight drop in temperature is a consequence of replacing with a new radiator. Continue to monitor the temperature with the scanner.
If the readings are stable for a long time and do not deteriorate, then everything is in order with your cooling system.
The next step is to replace the motor in the dashboard.
 

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2002 Chevy Trailblazer LT
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19 Posts
Discussion Starter #10
Yeah I’ll keep monitoring it. I wonder if the weather warming up during the summer will make it run hotter?
 

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2004 gmc envoy_slt
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2,325 Posts
The thermostat in these trucks is 195 deg, so that is where the actual temperature usually sits. The dash temp gauge is not that accurate, when engine actual temp is at 195, the gauge is at about 205 - 210.
A dip to 170 is kind of unusual, maybe a poor connection somewhere from sensor to PCM or a flaky temp sensor.
 

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Chevy Trailblazer 2008 LTZ (4.2L)
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Oh, I'm sorry Hud47 I looked at the wrong data and therefore gave the wrong answer.
Indeed, readings 175 and 190 are low.
 

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2002 Chevy Trailblazer LT
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Discussion Starter #13
So what would you suggest? How should I proceed? Thanks
 

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Chevy Trailblazer 2008 LTZ (4.2L)
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In fact, there can be only two problems.
1. Faulty thermostat (which is most likely)
2. The temperature sensor is defective.
If the thermostat is faulty, you will receive code P0128
If the temperature sensor fails, these will be codes P0117 and P0118
I think that most likely this is a problem with the thermostat and you need to prepare to replace it. Part number for your year GM P/N 12620112
Tell us what errors your OBD2 scanner shows.
 

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2004 gmc envoy_slt
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2,325 Posts
If you are going to replace the thermostat, you should also replace the temp sensor since they are in the same area.
 

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2002 Chevy Trailblazer LT
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Discussion Starter #16
I’m not getting any codes or CEL it got up to 190 today but that was the highest
 

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Chevy Trailblazer 2008 LTZ (4.2L)
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Do not worry, and just keep an eye on the temperature. If a breakdown occurs, the warning lamp CEL will surely light up.
 

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Chevy Trailblazer 2008 LTZ (4.2L)
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Error code P0128 will trigger when the coolant temperature is between 19-167 °F.
However, for its operation, additional conditions must also be fulfilled.
 
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