Engine Light - Thermostat or Cooling Sensor? - Chevy Colorado & GMC Canyon

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Old 11-09-2010, 12:18 PM   #1 (permalink)
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Default Engine Light - Thermostat or Cooling Sensor?

2005 Colorado, 127,000 miles, 4 cylinder engine.
Engine light came on yesterday & I went by Autozone to have them do the free diagnostic check.
The guy told me the code it gave indicated either low coolant level (level was fine), a bad cooling sensor or a bad thermostat.
The truck has never seemed to run hot, but I guess if a sensor was bad it probably wouldn't let me know anyway, huh?
How expensive would this be at a garage vs how difficult would it be to do myself?
The last thermostat I replaced was probably on a 68 El Camino, but I have done the throttle body cleaning & replaced spark plugs on my Colorado from how-to info given here.
Any advice appreciated!
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Old 11-10-2010, 02:53 AM   #2 (permalink)
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Default Re: Engine Light - Thermostat or Cooling Sensor?

Did he tell you what the code was?

I got the p0128 code and it was the thermostat. It was stuck open and did not let the engine reach proper operating temp.
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Old 11-10-2010, 11:16 PM   #3 (permalink)
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Default Re: Engine Light - Thermostat or Cooling Sensor?

No, he just said that's what the code indicated, one of those three possibilities.
For a $40 part, how difficult is changing the thermostat?
I've heard some crazy things, like there is no drain in the radiator...
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Old 11-11-2010, 02:43 AM   #4 (permalink)
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Default Re: Engine Light - Thermostat or Cooling Sensor?

Correct, there is no drain on the cooling system.

It's relatively simple. Raise the truck, remove the driver's side front wheel and the wheel well rubber splash shield. You will then see the lower radiator hose. Follow it to the block and you will find the t-stat housing/neck. Remove the two 10mm bolts then pull it back so you can remove the hose from the neck. You will lose about a quart to half gallon of coolant. Install the hose onto the new t-stat (be sure to line up the line on the hose with the notch on the t-stat housing to insure proper installation), bolt it back on the block and top off with coolant.
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Old 11-11-2010, 12:28 PM   #5 (permalink)
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Default Re: Engine Light - Thermostat or Cooling Sensor?

Hey, DBNissan, or anyone, really.
I "think" I saw this code come up before when we got hit by a nice cold blast last week. I didn't think anything of it so I just reset it. but I'm pretty sure it was the same P0128 code. During normal driving, my thermostat never reaches the first 1/4 mark. Matter of fact, this whole week in the 50s that temp needle never exceeded the halfway point between the Cold line and the first 1/4 mark line. If it was truly P0128, how long would it take for the CEL to come back on? I haven't had it on for 5-6 days now, and it's been 50's-60's every morning and evening...

It "seems" to me like I'm getting slightly better fuel economy this way...but what are some of the cons of leaving a stuck-open thermostat on?

ALSO, please be advise, I did a flush 2 years ago and filled up with 2 bottles of Redline Water Wetter, topped off the rest with 50/50 GM Coolant. About once a year the reserve drops under the full-cold line by one-finger or so and I just top off again.

It's funny because when I checked it then it was fine and I put it in the correct way in...or at least I think I did...I "think" the spring-mechanism goes facing away from the engine...but honestly I can't remember, I just know however it came out I put it back in the same exactly way.

any advise would be greatly appreciated.
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Old 11-11-2010, 06:14 PM   #6 (permalink)
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Default Re: Engine Light - Thermostat or Cooling Sensor?

The P0128 code will come on when the PCM detects that the engine does not reach a minimum operating temp within a certain amount of time based on IAT and ambient temp. I noticed on my scangauge that my temp was about 10-15F below the normal range of 195-205F that my truck used to operate in. I too did notice slightly better fuel economy at the beginning. However, the cooler temps will potentially prevent the PCM from switching to closed-loop. When the programming is in open-loop, the engine runs a little richer. That can lead to carbon deposit build-up and a clogged catalytic over an extended period of time. The carbon deposits alone will lower the fuel economy in the long run.

Which spring mechanism are you referring to?
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Old 11-15-2010, 11:30 AM   #7 (permalink)
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Default Re: Engine Light - Thermostat or Cooling Sensor?

Quote:
Originally Posted by DBNissan
Which spring mechanism are you referring to?
It's been a while so I don't even remember what our thermostat looks like, the "spring" side, or flat-side of the thermostat. Not he round "hub" side. I "think" it was set with the "spring"/"flat" side facing away from the engine...but honestly it's been so long I can't remember.

Last time I had the P0128 was 11/5/2010. So far today 11/15/2010 nothing yet...but I'm still keeping my eye on it for any CELs.
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I5, 3.42, 5sp
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Volant CAI w/ RamAir
HPTuners custom tune
200 RWTQ @ 4,200 RPM
207 RWHP @ 5,800 RPM
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Old 11-15-2010, 12:28 PM   #8 (permalink)
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Default Re: Engine Light - Thermostat or Cooling Sensor?

The t-stat can only go in one way. It's integrated into the housing. The housing and t-stat are sold as one unit.


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Old 11-17-2010, 12:36 PM   #9 (permalink)
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Default Re: Engine Light - Thermostat or Cooling Sensor?

looks like I had it backwards in my head.

What is the part number to this?

So far no CEL yet. Still waiting...
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2004 Colorado RegCab ZQ8
I5, 3.42, 5sp
Dynomax SuperTurbo Muffler
Volant CAI w/ RamAir
HPTuners custom tune
200 RWTQ @ 4,200 RPM
207 RWHP @ 5,800 RPM
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Old 12-21-2010, 02:22 PM   #10 (permalink)
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Default Re: Engine Light - Thermostat or Cooling Sensor?

Sorry I took a while to get back, but I'm getting the P0128 code.
From what I read here, lookes like the thermostat.
Any advice on replacing this?
Thanks!
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