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I have a 2012 Chevy Colorado with an odd temp gauge issue.

When the vehicle is started from being completely cold (like freezing cold), the temp gauge immediately goes all the way up. This leads me to believe it's just the gauge, not the actual temperature that's the issue.

After driving a bit, the needle is off the charts, and only stops because it literally hits the top of the dashboard.

No odd smells, smoke, sounds, performance, etc.

What could I do to troubleshoot it on my own?

  • I googled "2012 Chevy Colorado temperature sending unit", and this guy's issue and approach seem relevant to your situation. Give it a look. – elrobis Dec 7 '16 at 17:20
  • without looking at a wiring diagram i'd guess that the pcm takes a reading from the coolant temp sensor and passes the information to the cluster over a serial data line. you may just need to have a sweep test done on the cluster and possibly replace the motor for the temp gauge. – Ben Dec 7 '16 at 17:25
  • @Ben...ack...I'd try blindly and optimistically spending $20 on a new temp sending unit and just swapping it out before I'd crack open the dashboard and mess with the instrument cluster. Your rep signals considerably more experience than myself, but I think Occam's Razor absolutely has its place in the realm of auto repair.. – elrobis Dec 7 '16 at 17:28
  • Thanks for the help guys, I'll try to look at that temp sending unit. @elrobis - the rep is from the programming side of stack overflow so I'm happy for the suggestions from you all on this! – kthornbloom Dec 7 '16 at 20:33
  • By the way, if I don't get to this right away, would a bad temp sender cause other issues aside from the wonky gauge? – kthornbloom Dec 7 '16 at 20:35
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There are several possibility:

  • The temp gauge is bad

  • The thermostat is stuck: usually the thermostat will prevent the car from cooling itself until the engine has reached the operating temperature, then it will open to start the cooling process. If it is stuck open, the car will take forever to heat up, if it is stuck close, the car will overheat; but sometimes they open and work fine, but just not at the right time (it's a spring system)

  • We could look at the cooling pump, but as the car operates properly it's not the case.

  • The fans may be kicking in at the wrong time; was the ECU reprogrammed or swapped?

Try this:

make sure the car is cold; open the radiator cap, start the car and wait. when the car gets hot:

  • do you see the fluid moving? if not, investigate pump / thermostat
  • are the fans on? if not, investigate fan fuse / relay / ecu.
  • is the fluid bubbling? it should not get that hot during idle, so you re-investigate one of the problems above.
  • last, if it's all good but the temp looks like, just change the sensor to see what happens.
  • if your car has reverse cooling (like the LT1 engine for example), not bleeding air during a coolant change will create a hot air pocket in the system; if your car is one of those, bleed the air to see if it fixes the problem.
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I think you can diagnose it easily and diagnosis probably do not require any work under the hood. You, or your mechanic should connect to your OBD port and check what the computer thinks the temperature is.

The tools which can talk with the car computer make diagnosis much easier. So if you don't have any tools but you want to diagnose problems yourself, you may want to invest in some basic tools. The very basic OBD tools are very cheap and compatible with virtually all brands so it is a very good investment. The prices range from $20 to $200+

  • If the value is reasonable, then your instrument cluster is broken or needs calibration. Calibration probably require some more advanced software than basic OBD tools for accessing instrument cluster and updating its settings.

  • If the value is off the charts, then your sensor is broken. It is cheap enough to try to replace it. There may be some sort of short circuit, for example some goo is between the connectors and causing resistance of the sensor to go down. Normally when coolant heats, sensor resistance goes down. But if it already starts with a low value, it may cause this kind of behavior. You should be able to check the sensor value with ohm meter manually, in addition the car computer may report the value in ohm also.

But in my opinion your cluster has some problems because if the temperature sensor sent some strange values, there would be errors logged in the computer. This probably would turn on the check engine light. But again, you can simply check if there are errors logged with an OBD tool.

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So, if your sensor/sending unit is giving wrong data, your check engine light should be lit. If for some reason that didn't happen another way to check is by disconnecting the temp sensor altogether.

Based on the symptoms you've listed there can only be one of two:

  1. Bad Temp Sensor
  2. Bad cluster (probably with a random fried resistor somewhere on it)

Disconnecting the sensor or throwing a new one in is the best (and easiest) way to verify if the problem lies in the sensor. If that doesn't resolve it, then process of elimination would dictate that the gauge is the problem.

I 100% agree that avoiding tearing into the cluster is ideal, so check the sensor as a first step. This won't require any special tools or anything.


Cautions

Starting the truck with no sensor connected could cause some odd, annoying though non-damaging behavior. So I'd recommend throwing a new one on rather than just disconnecting. That said, if you're only interested in the gauge action, then you'll only need to run the truck for like 30 seconds or so to see what it does. Only reason for mentioning this, is don't run it for an extended period of time. While running the motor like that won't be particularly dangerous, driving it as usual without a temp sensor attached would be a very risky endeavor.


Why this conclusion?

Simply, any overheat condition wherein the motor is actually over heated, there will be other symptoms. Especially if it were actually overheating that much.

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