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Low temp gauge, no codes

16K views 10 replies 5 participants last post by  Super 88 
#1 ·
Did some searching but couldn't find someone with the same problem I'm having. I replaced my thermostat in February because my gauge was reading low and I had CEL light on. Took care of that problem.

Within the past couple weeks I've noticed that my needle rarely gets past 2nd hash mark to the left of 210. Occasionally the needle will read 210 but goes right back down. This would lead me to believe my thermostat may be going out again but why am I not getting any codes if it's almost constantly 2 hashes below 210? Any ideas fellas?

Also, I replaced my battery about 2 months ago and within this past week if I am just idling, my battery gauge dips down to about 12 and then back to roughly 15-16 and keeps doing this over and over. Also makes my HID's flicker. If I idle the engine up to about 1k rpm, the lights smooth out and the gauge sticks around 15. Could this be an alternator issue?
 
#3 ·
Could also be a bad replacement thermostat. I'd change both while I was in there.

Your other problem does sound like the alternator, or loose wiring, corroded connectors, or erratic idle. At idle, are you at a steady 600 RPM, or does it fluctuate? Have you ever cleaned the throttle body?
 
#5 ·
$20 it's your coolant temp sensor. Thermostats don't open and close that fast to cause fluctuations. When they go bad, they usually stick open and the temp stays steady, just too low.

The esteemed Roadie and I disagree on only one thing. (Well ... two, if you include who is better looking.)

He feels almost all the time it is the thermostat, and I feel that the coolant temp sensor fails almost as often as the thermostat.

My opinion: if the temp is low and steady, it is nearly always the thermostat. If the temp is low and fluctuates, it is nearly always the temp sensor.
 
#7 ·
CEL driving me crazy!!!

I recently replaced the coolant temp sensor due to the CEL being on. I ran a scan and got (2) error codes saying the sensor was the issue. After replacing the sensor, I drove the Envoy about 2 days with no trouble. Then after the car had been sitting for about 2 hours, I crank it up and the CEL comes on immediately. I rescan and get the same thing; coolant temp sensor x2. What's up with this? Prior to changing the coolant sensor, I just replaced the entire computer system and had it flashed by the dealer.
 
#9 ·
I recently replaced the coolant temp sensor due to the CEL being on. I ran a scan and got (2) error codes saying the sensor was the issue. After replacing the sensor, I drove the Envoy about 2 days with no trouble. Then after the car had been sitting for about 2 hours, I crank it up and the CEL comes on immediately. I rescan and get the same thing; coolant temp sensor x2. What's up with this? Prior to changing the coolant sensor, I just replaced the entire computer system and had it flashed by the dealer.
It would be helpful if you told us what code number you are getting.
 
#10 · (Edited)
The CEL illuminates after a certain period of low temps, but when it illuminates, it tends to be REALLY bad. A slight tick to the left doesn't show anything.

The problem is that the dash gauge is not linear. That slight tick to the left is actually a big drop in temps, and can certainly adversely affect your mileage.

As to changing both, we usually recommend folks do this just because it is a pain to get at both so once the alternator is out, you might as well. On the other hand, the sensor can be slapped in with little to no coolant loss, and the thermostat requires draining a fair amount of coolant, so if the indications are that it is the sensor and if you already changed the thermostat with a good brand-name one and if one feels lucky, it might be worth it to try the sensor first.

I did, and this is how I know the indications (fluctuating temps, especially on the highway) that it may be the sensor and not the thermostat this time.

Good luck and let us know how it works for you.



And ... by the way, I need to add that the Roadie has a million times more experience than me with these vehicles, but I still am better looking.

After all, I may be the most boring person on the face of the earth but I still get compared regularly to the Dos Equis guy ... and I once doubled for Dennis Farina in a movie!

Take THAT Roadie!

:):):)
 
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